1 // ignore-tidy-filelength
2
3 use super::{
4 DefIdOrName, FindExprBySpan, ImplCandidate, Obligation, ObligationCause, ObligationCauseCode,
5 PredicateObligation,
6 };
7
8 use crate::infer::InferCtxt;
9 use crate::traits::{NormalizeExt, ObligationCtxt};
10
11 use hir::def::CtorOf;
12 use rustc_data_structures::fx::FxHashSet;
13 use rustc_data_structures::stack::ensure_sufficient_stack;
14 use rustc_errors::{
15 error_code, pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder,
16 ErrorGuaranteed, MultiSpan, Style, SuggestionStyle,
17 };
18 use rustc_hir as hir;
19 use rustc_hir::def::DefKind;
20 use rustc_hir::def_id::DefId;
21 use rustc_hir::intravisit::Visitor;
22 use rustc_hir::is_range_literal;
23 use rustc_hir::lang_items::LangItem;
24 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node};
25 use rustc_hir::{Expr, HirId};
26 use rustc_infer::infer::error_reporting::TypeErrCtxt;
27 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
28 use rustc_infer::infer::{DefineOpaqueTypes, InferOk, LateBoundRegionConversionTime};
29 use rustc_middle::hir::map;
30 use rustc_middle::ty::error::TypeError::{self, Sorts};
31 use rustc_middle::ty::{
32 self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind,
33 GeneratorDiagnosticData, GeneratorInteriorTypeCause, InferTy, InternalSubsts, IsSuggestable,
34 ToPredicate, Ty, TyCtxt, TypeAndMut, TypeFoldable, TypeFolder, TypeSuperFoldable,
35 TypeVisitableExt, TypeckResults,
36 };
37 use rustc_span::def_id::LocalDefId;
38 use rustc_span::symbol::{sym, Ident, Symbol};
39 use rustc_span::{BytePos, DesugaringKind, ExpnKind, MacroKind, Span, DUMMY_SP};
40 use rustc_target::spec::abi;
41 use std::borrow::Cow;
42 use std::iter;
43 use std::ops::Deref;
44
45 use super::InferCtxtPrivExt;
46 use crate::infer::InferCtxtExt as _;
47 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
48 use rustc_middle::ty::print::{with_forced_trimmed_paths, with_no_trimmed_paths};
49
50 #[derive(Debug)]
51 pub enum GeneratorInteriorOrUpvar {
52 // span of interior type
53 Interior(Span, Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>),
54 // span of upvar
55 Upvar(Span),
56 }
57
58 // This type provides a uniform interface to retrieve data on generators, whether it originated from
59 // the local crate being compiled or from a foreign crate.
60 #[derive(Debug)]
61 pub enum GeneratorData<'tcx, 'a> {
62 Local(&'a TypeckResults<'tcx>),
63 Foreign(&'tcx GeneratorDiagnosticData<'tcx>),
64 }
65
66 impl<'tcx, 'a> GeneratorData<'tcx, 'a> {
67 // Try to get information about variables captured by the generator that matches a type we are
68 // looking for with `ty_matches` function. We uses it to find upvar which causes a failure to
69 // meet an obligation
try_get_upvar_span<F>( &self, infer_context: &InferCtxt<'tcx>, generator_did: DefId, ty_matches: F, ) -> Option<GeneratorInteriorOrUpvar> where F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,70 fn try_get_upvar_span<F>(
71 &self,
72 infer_context: &InferCtxt<'tcx>,
73 generator_did: DefId,
74 ty_matches: F,
75 ) -> Option<GeneratorInteriorOrUpvar>
76 where
77 F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,
78 {
79 match self {
80 GeneratorData::Local(typeck_results) => {
81 infer_context.tcx.upvars_mentioned(generator_did).and_then(|upvars| {
82 upvars.iter().find_map(|(upvar_id, upvar)| {
83 let upvar_ty = typeck_results.node_type(*upvar_id);
84 let upvar_ty = infer_context.resolve_vars_if_possible(upvar_ty);
85 ty_matches(ty::Binder::dummy(upvar_ty))
86 .then(|| GeneratorInteriorOrUpvar::Upvar(upvar.span))
87 })
88 })
89 }
90 GeneratorData::Foreign(_) => None,
91 }
92 }
93
94 // Try to get the span of a type being awaited on that matches the type we are looking with the
95 // `ty_matches` function. We uses it to find awaited type which causes a failure to meet an
96 // obligation
get_from_await_ty<F>( &self, tcx: TyCtxt<'tcx>, visitor: AwaitsVisitor, hir: map::Map<'tcx>, ty_matches: F, ) -> Option<Span> where F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,97 fn get_from_await_ty<F>(
98 &self,
99 tcx: TyCtxt<'tcx>,
100 visitor: AwaitsVisitor,
101 hir: map::Map<'tcx>,
102 ty_matches: F,
103 ) -> Option<Span>
104 where
105 F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,
106 {
107 match self {
108 GeneratorData::Local(typeck_results) => visitor
109 .awaits
110 .into_iter()
111 .map(|id| hir.expect_expr(id))
112 .find(|await_expr| {
113 ty_matches(ty::Binder::dummy(typeck_results.expr_ty_adjusted(&await_expr)))
114 })
115 .map(|expr| expr.span),
116 GeneratorData::Foreign(generator_diagnostic_data) => visitor
117 .awaits
118 .into_iter()
119 .map(|id| hir.expect_expr(id))
120 .find(|await_expr| {
121 ty_matches(ty::Binder::dummy(
122 generator_diagnostic_data
123 .adjustments
124 .get(&await_expr.hir_id.local_id)
125 .map_or::<&[ty::adjustment::Adjustment<'tcx>], _>(&[], |a| &a[..])
126 .last()
127 .map_or_else::<Ty<'tcx>, _, _>(
128 || {
129 generator_diagnostic_data
130 .nodes_types
131 .get(&await_expr.hir_id.local_id)
132 .cloned()
133 .unwrap_or_else(|| {
134 bug!(
135 "node_type: no type for node {}",
136 tcx.hir().node_to_string(await_expr.hir_id)
137 )
138 })
139 },
140 |adj| adj.target,
141 ),
142 ))
143 })
144 .map(|expr| expr.span),
145 }
146 }
147
148 /// Get the type, expression, span and optional scope span of all types
149 /// that are live across the yield of this generator
get_generator_interior_types( &self, ) -> ty::Binder<'tcx, &[GeneratorInteriorTypeCause<'tcx>]>150 fn get_generator_interior_types(
151 &self,
152 ) -> ty::Binder<'tcx, &[GeneratorInteriorTypeCause<'tcx>]> {
153 match self {
154 GeneratorData::Local(typeck_result) => {
155 typeck_result.generator_interior_types.as_deref()
156 }
157 GeneratorData::Foreign(generator_diagnostic_data) => {
158 generator_diagnostic_data.generator_interior_types.as_deref()
159 }
160 }
161 }
162
163 // Used to get the source of the data, note we don't have as much information for generators
164 // originated from foreign crates
is_foreign(&self) -> bool165 fn is_foreign(&self) -> bool {
166 match self {
167 GeneratorData::Local(_) => false,
168 GeneratorData::Foreign(_) => true,
169 }
170 }
171 }
172
173 // This trait is public to expose the diagnostics methods to clippy.
174 pub trait TypeErrCtxtExt<'tcx> {
suggest_restricting_param_bound( &self, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, associated_item: Option<(&'static str, Ty<'tcx>)>, body_id: LocalDefId, )175 fn suggest_restricting_param_bound(
176 &self,
177 err: &mut Diagnostic,
178 trait_pred: ty::PolyTraitPredicate<'tcx>,
179 associated_item: Option<(&'static str, Ty<'tcx>)>,
180 body_id: LocalDefId,
181 );
182
suggest_dereferences( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool183 fn suggest_dereferences(
184 &self,
185 obligation: &PredicateObligation<'tcx>,
186 err: &mut Diagnostic,
187 trait_pred: ty::PolyTraitPredicate<'tcx>,
188 ) -> bool;
189
get_closure_name( &self, def_id: DefId, err: &mut Diagnostic, msg: Cow<'static, str>, ) -> Option<Symbol>190 fn get_closure_name(
191 &self,
192 def_id: DefId,
193 err: &mut Diagnostic,
194 msg: Cow<'static, str>,
195 ) -> Option<Symbol>;
196
suggest_fn_call( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool197 fn suggest_fn_call(
198 &self,
199 obligation: &PredicateObligation<'tcx>,
200 err: &mut Diagnostic,
201 trait_pred: ty::PolyTraitPredicate<'tcx>,
202 ) -> bool;
203
check_for_binding_assigned_block_without_tail_expression( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )204 fn check_for_binding_assigned_block_without_tail_expression(
205 &self,
206 obligation: &PredicateObligation<'tcx>,
207 err: &mut Diagnostic,
208 trait_pred: ty::PolyTraitPredicate<'tcx>,
209 );
210
suggest_add_clone_to_arg( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool211 fn suggest_add_clone_to_arg(
212 &self,
213 obligation: &PredicateObligation<'tcx>,
214 err: &mut Diagnostic,
215 trait_pred: ty::PolyTraitPredicate<'tcx>,
216 ) -> bool;
217
extract_callable_info( &self, body_id: LocalDefId, param_env: ty::ParamEnv<'tcx>, found: Ty<'tcx>, ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)>218 fn extract_callable_info(
219 &self,
220 body_id: LocalDefId,
221 param_env: ty::ParamEnv<'tcx>,
222 found: Ty<'tcx>,
223 ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)>;
224
suggest_add_reference_to_arg( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, has_custom_message: bool, ) -> bool225 fn suggest_add_reference_to_arg(
226 &self,
227 obligation: &PredicateObligation<'tcx>,
228 err: &mut Diagnostic,
229 trait_pred: ty::PolyTraitPredicate<'tcx>,
230 has_custom_message: bool,
231 ) -> bool;
232
suggest_borrowing_for_object_cast( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, self_ty: Ty<'tcx>, object_ty: Ty<'tcx>, )233 fn suggest_borrowing_for_object_cast(
234 &self,
235 err: &mut Diagnostic,
236 obligation: &PredicateObligation<'tcx>,
237 self_ty: Ty<'tcx>,
238 object_ty: Ty<'tcx>,
239 );
240
suggest_remove_reference( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool241 fn suggest_remove_reference(
242 &self,
243 obligation: &PredicateObligation<'tcx>,
244 err: &mut Diagnostic,
245 trait_pred: ty::PolyTraitPredicate<'tcx>,
246 ) -> bool;
247
suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic)248 fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic);
249
suggest_change_mut( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )250 fn suggest_change_mut(
251 &self,
252 obligation: &PredicateObligation<'tcx>,
253 err: &mut Diagnostic,
254 trait_pred: ty::PolyTraitPredicate<'tcx>,
255 );
256
suggest_semicolon_removal( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, span: Span, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool257 fn suggest_semicolon_removal(
258 &self,
259 obligation: &PredicateObligation<'tcx>,
260 err: &mut Diagnostic,
261 span: Span,
262 trait_pred: ty::PolyTraitPredicate<'tcx>,
263 ) -> bool;
264
return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>265 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>;
266
suggest_impl_trait( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool267 fn suggest_impl_trait(
268 &self,
269 err: &mut Diagnostic,
270 obligation: &PredicateObligation<'tcx>,
271 trait_pred: ty::PolyTraitPredicate<'tcx>,
272 ) -> bool;
273
point_at_returns_when_relevant( &self, err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>, obligation: &PredicateObligation<'tcx>, )274 fn point_at_returns_when_relevant(
275 &self,
276 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
277 obligation: &PredicateObligation<'tcx>,
278 );
279
report_closure_arg_mismatch( &self, span: Span, found_span: Option<Span>, found: ty::PolyTraitRef<'tcx>, expected: ty::PolyTraitRef<'tcx>, cause: &ObligationCauseCode<'tcx>, found_node: Option<Node<'_>>, param_env: ty::ParamEnv<'tcx>, ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>280 fn report_closure_arg_mismatch(
281 &self,
282 span: Span,
283 found_span: Option<Span>,
284 found: ty::PolyTraitRef<'tcx>,
285 expected: ty::PolyTraitRef<'tcx>,
286 cause: &ObligationCauseCode<'tcx>,
287 found_node: Option<Node<'_>>,
288 param_env: ty::ParamEnv<'tcx>,
289 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
290
note_conflicting_closure_bounds( &self, cause: &ObligationCauseCode<'tcx>, err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>, )291 fn note_conflicting_closure_bounds(
292 &self,
293 cause: &ObligationCauseCode<'tcx>,
294 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
295 );
296
suggest_fully_qualified_path( &self, err: &mut Diagnostic, item_def_id: DefId, span: Span, trait_ref: DefId, )297 fn suggest_fully_qualified_path(
298 &self,
299 err: &mut Diagnostic,
300 item_def_id: DefId,
301 span: Span,
302 trait_ref: DefId,
303 );
304
maybe_note_obligation_cause_for_async_await( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, ) -> bool305 fn maybe_note_obligation_cause_for_async_await(
306 &self,
307 err: &mut Diagnostic,
308 obligation: &PredicateObligation<'tcx>,
309 ) -> bool;
310
note_obligation_cause_for_async_await( &self, err: &mut Diagnostic, interior_or_upvar_span: GeneratorInteriorOrUpvar, is_async: bool, outer_generator: Option<DefId>, trait_pred: ty::TraitPredicate<'tcx>, target_ty: Ty<'tcx>, typeck_results: Option<&ty::TypeckResults<'tcx>>, obligation: &PredicateObligation<'tcx>, next_code: Option<&ObligationCauseCode<'tcx>>, )311 fn note_obligation_cause_for_async_await(
312 &self,
313 err: &mut Diagnostic,
314 interior_or_upvar_span: GeneratorInteriorOrUpvar,
315 is_async: bool,
316 outer_generator: Option<DefId>,
317 trait_pred: ty::TraitPredicate<'tcx>,
318 target_ty: Ty<'tcx>,
319 typeck_results: Option<&ty::TypeckResults<'tcx>>,
320 obligation: &PredicateObligation<'tcx>,
321 next_code: Option<&ObligationCauseCode<'tcx>>,
322 );
323
note_obligation_cause_code<T>( &self, body_id: LocalDefId, err: &mut Diagnostic, predicate: T, param_env: ty::ParamEnv<'tcx>, cause_code: &ObligationCauseCode<'tcx>, obligated_types: &mut Vec<Ty<'tcx>>, seen_requirements: &mut FxHashSet<DefId>, ) where T: ToPredicate<'tcx>324 fn note_obligation_cause_code<T>(
325 &self,
326 body_id: LocalDefId,
327 err: &mut Diagnostic,
328 predicate: T,
329 param_env: ty::ParamEnv<'tcx>,
330 cause_code: &ObligationCauseCode<'tcx>,
331 obligated_types: &mut Vec<Ty<'tcx>>,
332 seen_requirements: &mut FxHashSet<DefId>,
333 ) where
334 T: ToPredicate<'tcx>;
335
336 /// Suggest to await before try: future? => future.await?
suggest_await_before_try( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, trait_pred: ty::PolyTraitPredicate<'tcx>, span: Span, )337 fn suggest_await_before_try(
338 &self,
339 err: &mut Diagnostic,
340 obligation: &PredicateObligation<'tcx>,
341 trait_pred: ty::PolyTraitPredicate<'tcx>,
342 span: Span,
343 );
344
suggest_floating_point_literal( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_ref: &ty::PolyTraitRef<'tcx>, )345 fn suggest_floating_point_literal(
346 &self,
347 obligation: &PredicateObligation<'tcx>,
348 err: &mut Diagnostic,
349 trait_ref: &ty::PolyTraitRef<'tcx>,
350 );
351
suggest_derive( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )352 fn suggest_derive(
353 &self,
354 obligation: &PredicateObligation<'tcx>,
355 err: &mut Diagnostic,
356 trait_pred: ty::PolyTraitPredicate<'tcx>,
357 );
358
suggest_dereferencing_index( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )359 fn suggest_dereferencing_index(
360 &self,
361 obligation: &PredicateObligation<'tcx>,
362 err: &mut Diagnostic,
363 trait_pred: ty::PolyTraitPredicate<'tcx>,
364 );
365
suggest_option_method_if_applicable( &self, failed_pred: ty::Predicate<'tcx>, param_env: ty::ParamEnv<'tcx>, err: &mut Diagnostic, expr: &hir::Expr<'_>, )366 fn suggest_option_method_if_applicable(
367 &self,
368 failed_pred: ty::Predicate<'tcx>,
369 param_env: ty::ParamEnv<'tcx>,
370 err: &mut Diagnostic,
371 expr: &hir::Expr<'_>,
372 );
373
note_function_argument_obligation( &self, body_id: LocalDefId, err: &mut Diagnostic, arg_hir_id: HirId, parent_code: &ObligationCauseCode<'tcx>, param_env: ty::ParamEnv<'tcx>, predicate: ty::Predicate<'tcx>, call_hir_id: HirId, )374 fn note_function_argument_obligation(
375 &self,
376 body_id: LocalDefId,
377 err: &mut Diagnostic,
378 arg_hir_id: HirId,
379 parent_code: &ObligationCauseCode<'tcx>,
380 param_env: ty::ParamEnv<'tcx>,
381 predicate: ty::Predicate<'tcx>,
382 call_hir_id: HirId,
383 );
point_at_chain( &self, expr: &hir::Expr<'_>, typeck_results: &TypeckResults<'tcx>, type_diffs: Vec<TypeError<'tcx>>, param_env: ty::ParamEnv<'tcx>, err: &mut Diagnostic, )384 fn point_at_chain(
385 &self,
386 expr: &hir::Expr<'_>,
387 typeck_results: &TypeckResults<'tcx>,
388 type_diffs: Vec<TypeError<'tcx>>,
389 param_env: ty::ParamEnv<'tcx>,
390 err: &mut Diagnostic,
391 );
probe_assoc_types_at_expr( &self, type_diffs: &[TypeError<'tcx>], span: Span, prev_ty: Ty<'tcx>, body_id: hir::HirId, param_env: ty::ParamEnv<'tcx>, ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>>392 fn probe_assoc_types_at_expr(
393 &self,
394 type_diffs: &[TypeError<'tcx>],
395 span: Span,
396 prev_ty: Ty<'tcx>,
397 body_id: hir::HirId,
398 param_env: ty::ParamEnv<'tcx>,
399 ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>>;
400
maybe_suggest_convert_to_slice( &self, err: &mut Diagnostic, trait_ref: ty::PolyTraitRef<'tcx>, candidate_impls: &[ImplCandidate<'tcx>], span: Span, )401 fn maybe_suggest_convert_to_slice(
402 &self,
403 err: &mut Diagnostic,
404 trait_ref: ty::PolyTraitRef<'tcx>,
405 candidate_impls: &[ImplCandidate<'tcx>],
406 span: Span,
407 );
408 }
409
predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String)410 fn predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String) {
411 (
412 generics.tail_span_for_predicate_suggestion(),
413 format!("{} {}", generics.add_where_or_trailing_comma(), pred),
414 )
415 }
416
417 /// Type parameter needs more bounds. The trivial case is `T` `where T: Bound`, but
418 /// it can also be an `impl Trait` param that needs to be decomposed to a type
419 /// param for cleaner code.
suggest_restriction<'tcx>( tcx: TyCtxt<'tcx>, item_id: LocalDefId, hir_generics: &hir::Generics<'tcx>, msg: &str, err: &mut Diagnostic, fn_sig: Option<&hir::FnSig<'_>>, projection: Option<&ty::AliasTy<'_>>, trait_pred: ty::PolyTraitPredicate<'tcx>, super_traits: Option<(&Ident, &hir::GenericBounds<'_>)>, )420 fn suggest_restriction<'tcx>(
421 tcx: TyCtxt<'tcx>,
422 item_id: LocalDefId,
423 hir_generics: &hir::Generics<'tcx>,
424 msg: &str,
425 err: &mut Diagnostic,
426 fn_sig: Option<&hir::FnSig<'_>>,
427 projection: Option<&ty::AliasTy<'_>>,
428 trait_pred: ty::PolyTraitPredicate<'tcx>,
429 // When we are dealing with a trait, `super_traits` will be `Some`:
430 // Given `trait T: A + B + C {}`
431 // - ^^^^^^^^^ GenericBounds
432 // |
433 // &Ident
434 super_traits: Option<(&Ident, &hir::GenericBounds<'_>)>,
435 ) {
436 if hir_generics.where_clause_span.from_expansion()
437 || hir_generics.where_clause_span.desugaring_kind().is_some()
438 || projection.is_some_and(|projection| tcx.opt_rpitit_info(projection.def_id).is_some())
439 {
440 return;
441 }
442 let generics = tcx.generics_of(item_id);
443 // Given `fn foo(t: impl Trait)` where `Trait` requires assoc type `A`...
444 if let Some((param, bound_str, fn_sig)) =
445 fn_sig.zip(projection).and_then(|(sig, p)| match p.self_ty().kind() {
446 // Shenanigans to get the `Trait` from the `impl Trait`.
447 ty::Param(param) => {
448 let param_def = generics.type_param(param, tcx);
449 if param_def.kind.is_synthetic() {
450 let bound_str =
451 param_def.name.as_str().strip_prefix("impl ")?.trim_start().to_string();
452 return Some((param_def, bound_str, sig));
453 }
454 None
455 }
456 _ => None,
457 })
458 {
459 let type_param_name = hir_generics.params.next_type_param_name(Some(&bound_str));
460 let trait_pred = trait_pred.fold_with(&mut ReplaceImplTraitFolder {
461 tcx,
462 param,
463 replace_ty: ty::ParamTy::new(generics.count() as u32, Symbol::intern(&type_param_name))
464 .to_ty(tcx),
465 });
466 if !trait_pred.is_suggestable(tcx, false) {
467 return;
468 }
469 // We know we have an `impl Trait` that doesn't satisfy a required projection.
470
471 // Find all of the occurrences of `impl Trait` for `Trait` in the function arguments'
472 // types. There should be at least one, but there might be *more* than one. In that
473 // case we could just ignore it and try to identify which one needs the restriction,
474 // but instead we choose to suggest replacing all instances of `impl Trait` with `T`
475 // where `T: Trait`.
476 let mut ty_spans = vec![];
477 for input in fn_sig.decl.inputs {
478 ReplaceImplTraitVisitor { ty_spans: &mut ty_spans, param_did: param.def_id }
479 .visit_ty(input);
480 }
481 // The type param `T: Trait` we will suggest to introduce.
482 let type_param = format!("{}: {}", type_param_name, bound_str);
483
484 let mut sugg = vec![
485 if let Some(span) = hir_generics.span_for_param_suggestion() {
486 (span, format!(", {}", type_param))
487 } else {
488 (hir_generics.span, format!("<{}>", type_param))
489 },
490 // `fn foo(t: impl Trait)`
491 // ^ suggest `where <T as Trait>::A: Bound`
492 predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
493 ];
494 sugg.extend(ty_spans.into_iter().map(|s| (s, type_param_name.to_string())));
495
496 // Suggest `fn foo<T: Trait>(t: T) where <T as Trait>::A: Bound`.
497 // FIXME: once `#![feature(associated_type_bounds)]` is stabilized, we should suggest
498 // `fn foo(t: impl Trait<A: Bound>)` instead.
499 err.multipart_suggestion(
500 "introduce a type parameter with a trait bound instead of using `impl Trait`",
501 sugg,
502 Applicability::MaybeIncorrect,
503 );
504 } else {
505 if !trait_pred.is_suggestable(tcx, false) {
506 return;
507 }
508 // Trivial case: `T` needs an extra bound: `T: Bound`.
509 let (sp, suggestion) = match (
510 hir_generics
511 .params
512 .iter()
513 .find(|p| !matches!(p.kind, hir::GenericParamKind::Type { synthetic: true, .. })),
514 super_traits,
515 ) {
516 (_, None) => predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
517 (None, Some((ident, []))) => (
518 ident.span.shrink_to_hi(),
519 format!(": {}", trait_pred.print_modifiers_and_trait_path()),
520 ),
521 (_, Some((_, [.., bounds]))) => (
522 bounds.span().shrink_to_hi(),
523 format!(" + {}", trait_pred.print_modifiers_and_trait_path()),
524 ),
525 (Some(_), Some((_, []))) => (
526 hir_generics.span.shrink_to_hi(),
527 format!(": {}", trait_pred.print_modifiers_and_trait_path()),
528 ),
529 };
530
531 err.span_suggestion_verbose(
532 sp,
533 format!("consider further restricting {}", msg),
534 suggestion,
535 Applicability::MachineApplicable,
536 );
537 }
538 }
539
540 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
suggest_restricting_param_bound( &self, mut err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, associated_ty: Option<(&'static str, Ty<'tcx>)>, mut body_id: LocalDefId, )541 fn suggest_restricting_param_bound(
542 &self,
543 mut err: &mut Diagnostic,
544 trait_pred: ty::PolyTraitPredicate<'tcx>,
545 associated_ty: Option<(&'static str, Ty<'tcx>)>,
546 mut body_id: LocalDefId,
547 ) {
548 if trait_pred.skip_binder().polarity == ty::ImplPolarity::Negative {
549 return;
550 }
551
552 let trait_pred = self.resolve_numeric_literals_with_default(trait_pred);
553
554 let self_ty = trait_pred.skip_binder().self_ty();
555 let (param_ty, projection) = match self_ty.kind() {
556 ty::Param(_) => (true, None),
557 ty::Alias(ty::Projection, projection) => (false, Some(projection)),
558 _ => (false, None),
559 };
560
561 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
562 // don't suggest `T: Sized + ?Sized`.
563 while let Some(node) = self.tcx.hir().find_by_def_id(body_id) {
564 match node {
565 hir::Node::Item(hir::Item {
566 ident,
567 kind: hir::ItemKind::Trait(_, _, generics, bounds, _),
568 ..
569 }) if self_ty == self.tcx.types.self_param => {
570 assert!(param_ty);
571 // Restricting `Self` for a single method.
572 suggest_restriction(
573 self.tcx,
574 body_id,
575 &generics,
576 "`Self`",
577 err,
578 None,
579 projection,
580 trait_pred,
581 Some((ident, bounds)),
582 );
583 return;
584 }
585
586 hir::Node::TraitItem(hir::TraitItem {
587 generics,
588 kind: hir::TraitItemKind::Fn(..),
589 ..
590 }) if self_ty == self.tcx.types.self_param => {
591 assert!(param_ty);
592 // Restricting `Self` for a single method.
593 suggest_restriction(
594 self.tcx, body_id, &generics, "`Self`", err, None, projection, trait_pred,
595 None,
596 );
597 return;
598 }
599
600 hir::Node::TraitItem(hir::TraitItem {
601 generics,
602 kind: hir::TraitItemKind::Fn(fn_sig, ..),
603 ..
604 })
605 | hir::Node::ImplItem(hir::ImplItem {
606 generics,
607 kind: hir::ImplItemKind::Fn(fn_sig, ..),
608 ..
609 })
610 | hir::Node::Item(hir::Item {
611 kind: hir::ItemKind::Fn(fn_sig, generics, _), ..
612 }) if projection.is_some() => {
613 // Missing restriction on associated type of type parameter (unmet projection).
614 suggest_restriction(
615 self.tcx,
616 body_id,
617 &generics,
618 "the associated type",
619 err,
620 Some(fn_sig),
621 projection,
622 trait_pred,
623 None,
624 );
625 return;
626 }
627 hir::Node::Item(hir::Item {
628 kind:
629 hir::ItemKind::Trait(_, _, generics, ..)
630 | hir::ItemKind::Impl(hir::Impl { generics, .. }),
631 ..
632 }) if projection.is_some() => {
633 // Missing restriction on associated type of type parameter (unmet projection).
634 suggest_restriction(
635 self.tcx,
636 body_id,
637 &generics,
638 "the associated type",
639 err,
640 None,
641 projection,
642 trait_pred,
643 None,
644 );
645 return;
646 }
647
648 hir::Node::Item(hir::Item {
649 kind:
650 hir::ItemKind::Struct(_, generics)
651 | hir::ItemKind::Enum(_, generics)
652 | hir::ItemKind::Union(_, generics)
653 | hir::ItemKind::Trait(_, _, generics, ..)
654 | hir::ItemKind::Impl(hir::Impl { generics, .. })
655 | hir::ItemKind::Fn(_, generics, _)
656 | hir::ItemKind::TyAlias(_, generics)
657 | hir::ItemKind::TraitAlias(generics, _)
658 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
659 ..
660 })
661 | hir::Node::TraitItem(hir::TraitItem { generics, .. })
662 | hir::Node::ImplItem(hir::ImplItem { generics, .. })
663 if param_ty =>
664 {
665 // We skip the 0'th subst (self) because we do not want
666 // to consider the predicate as not suggestible if the
667 // self type is an arg position `impl Trait` -- instead,
668 // we handle that by adding ` + Bound` below.
669 // FIXME(compiler-errors): It would be nice to do the same
670 // this that we do in `suggest_restriction` and pull the
671 // `impl Trait` into a new generic if it shows up somewhere
672 // else in the predicate.
673 if !trait_pred.skip_binder().trait_ref.substs[1..]
674 .iter()
675 .all(|g| g.is_suggestable(self.tcx, false))
676 {
677 return;
678 }
679 // Missing generic type parameter bound.
680 let param_name = self_ty.to_string();
681 let mut constraint = with_no_trimmed_paths!(
682 trait_pred.print_modifiers_and_trait_path().to_string()
683 );
684
685 if let Some((name, term)) = associated_ty {
686 // FIXME: this case overlaps with code in TyCtxt::note_and_explain_type_err.
687 // That should be extracted into a helper function.
688 if constraint.ends_with('>') {
689 constraint = format!(
690 "{}, {} = {}>",
691 &constraint[..constraint.len() - 1],
692 name,
693 term
694 );
695 } else {
696 constraint.push_str(&format!("<{} = {}>", name, term));
697 }
698 }
699
700 if suggest_constraining_type_param(
701 self.tcx,
702 generics,
703 &mut err,
704 ¶m_name,
705 &constraint,
706 Some(trait_pred.def_id()),
707 None,
708 ) {
709 return;
710 }
711 }
712
713 hir::Node::Item(hir::Item {
714 kind:
715 hir::ItemKind::Struct(_, generics)
716 | hir::ItemKind::Enum(_, generics)
717 | hir::ItemKind::Union(_, generics)
718 | hir::ItemKind::Trait(_, _, generics, ..)
719 | hir::ItemKind::Impl(hir::Impl { generics, .. })
720 | hir::ItemKind::Fn(_, generics, _)
721 | hir::ItemKind::TyAlias(_, generics)
722 | hir::ItemKind::TraitAlias(generics, _)
723 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
724 ..
725 }) if !param_ty => {
726 // Missing generic type parameter bound.
727 if suggest_arbitrary_trait_bound(
728 self.tcx,
729 generics,
730 &mut err,
731 trait_pred,
732 associated_ty,
733 ) {
734 return;
735 }
736 }
737 hir::Node::Crate(..) => return,
738
739 _ => {}
740 }
741 body_id = self.tcx.local_parent(body_id);
742 }
743 }
744
745 /// When after several dereferencing, the reference satisfies the trait
746 /// binding. This function provides dereference suggestion for this
747 /// specific situation.
suggest_dereferences( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool748 fn suggest_dereferences(
749 &self,
750 obligation: &PredicateObligation<'tcx>,
751 err: &mut Diagnostic,
752 trait_pred: ty::PolyTraitPredicate<'tcx>,
753 ) -> bool {
754 // It only make sense when suggesting dereferences for arguments
755 let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, call_hir_id, .. } = obligation.cause.code()
756 else { return false; };
757 let Some(typeck_results) = &self.typeck_results
758 else { return false; };
759 let hir::Node::Expr(expr) = self.tcx.hir().get(*arg_hir_id)
760 else { return false; };
761 let Some(arg_ty) = typeck_results.expr_ty_adjusted_opt(expr)
762 else { return false; };
763
764 let span = obligation.cause.span;
765 let mut real_trait_pred = trait_pred;
766 let mut code = obligation.cause.code();
767 while let Some((parent_code, parent_trait_pred)) = code.parent() {
768 code = parent_code;
769 if let Some(parent_trait_pred) = parent_trait_pred {
770 real_trait_pred = parent_trait_pred;
771 }
772
773 let real_ty = real_trait_pred.self_ty();
774 // We `erase_late_bound_regions` here because `make_subregion` does not handle
775 // `ReLateBound`, and we don't particularly care about the regions.
776 if !self.can_eq(
777 obligation.param_env,
778 self.tcx.erase_late_bound_regions(real_ty),
779 arg_ty,
780 ) {
781 continue;
782 }
783
784 if let ty::Ref(region, base_ty, mutbl) = *real_ty.skip_binder().kind() {
785 let autoderef = (self.autoderef_steps)(base_ty);
786 if let Some(steps) =
787 autoderef.into_iter().enumerate().find_map(|(steps, (ty, obligations))| {
788 // Re-add the `&`
789 let ty = Ty::new_ref(self.tcx, region, TypeAndMut { ty, mutbl });
790
791 // Remapping bound vars here
792 let real_trait_pred_and_ty =
793 real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, ty));
794 let obligation = self.mk_trait_obligation_with_new_self_ty(
795 obligation.param_env,
796 real_trait_pred_and_ty,
797 );
798 let may_hold = obligations
799 .iter()
800 .chain([&obligation])
801 .all(|obligation| self.predicate_may_hold(obligation))
802 .then_some(steps);
803
804 may_hold
805 })
806 {
807 if steps > 0 {
808 // Don't care about `&mut` because `DerefMut` is used less
809 // often and user will not expect autoderef happens.
810 if let Some(hir::Node::Expr(hir::Expr {
811 kind:
812 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, expr),
813 ..
814 })) = self.tcx.hir().find(*arg_hir_id)
815 {
816 let derefs = "*".repeat(steps);
817 err.span_suggestion_verbose(
818 expr.span.shrink_to_lo(),
819 "consider dereferencing here",
820 derefs,
821 Applicability::MachineApplicable,
822 );
823 return true;
824 }
825 }
826 } else if real_trait_pred != trait_pred {
827 // This branch addresses #87437.
828
829 // Remapping bound vars here
830 let real_trait_pred_and_base_ty =
831 real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, base_ty));
832 let obligation = self.mk_trait_obligation_with_new_self_ty(
833 obligation.param_env,
834 real_trait_pred_and_base_ty,
835 );
836 if self.predicate_may_hold(&obligation) {
837 let call_node = self.tcx.hir().get(*call_hir_id);
838 let msg = "consider dereferencing here";
839 let is_receiver = matches!(
840 call_node,
841 Node::Expr(hir::Expr {
842 kind: hir::ExprKind::MethodCall(_, receiver_expr, ..),
843 ..
844 })
845 if receiver_expr.hir_id == *arg_hir_id
846 );
847 if is_receiver {
848 err.multipart_suggestion_verbose(
849 msg,
850 vec![
851 (span.shrink_to_lo(), "(*".to_string()),
852 (span.shrink_to_hi(), ")".to_string()),
853 ],
854 Applicability::MachineApplicable,
855 )
856 } else {
857 err.span_suggestion_verbose(
858 span.shrink_to_lo(),
859 msg,
860 '*',
861 Applicability::MachineApplicable,
862 )
863 };
864 return true;
865 }
866 }
867 }
868 }
869 false
870 }
871
872 /// Given a closure's `DefId`, return the given name of the closure.
873 ///
874 /// This doesn't account for reassignments, but it's only used for suggestions.
get_closure_name( &self, def_id: DefId, err: &mut Diagnostic, msg: Cow<'static, str>, ) -> Option<Symbol>875 fn get_closure_name(
876 &self,
877 def_id: DefId,
878 err: &mut Diagnostic,
879 msg: Cow<'static, str>,
880 ) -> Option<Symbol> {
881 let get_name = |err: &mut Diagnostic, kind: &hir::PatKind<'_>| -> Option<Symbol> {
882 // Get the local name of this closure. This can be inaccurate because
883 // of the possibility of reassignment, but this should be good enough.
884 match &kind {
885 hir::PatKind::Binding(hir::BindingAnnotation::NONE, _, ident, None) => {
886 Some(ident.name)
887 }
888 _ => {
889 err.note(msg);
890 None
891 }
892 }
893 };
894
895 let hir = self.tcx.hir();
896 let hir_id = hir.local_def_id_to_hir_id(def_id.as_local()?);
897 match hir.find_parent(hir_id) {
898 Some(hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(local), .. })) => {
899 get_name(err, &local.pat.kind)
900 }
901 // Different to previous arm because one is `&hir::Local` and the other
902 // is `P<hir::Local>`.
903 Some(hir::Node::Local(local)) => get_name(err, &local.pat.kind),
904 _ => None,
905 }
906 }
907
908 /// We tried to apply the bound to an `fn` or closure. Check whether calling it would
909 /// evaluate to a type that *would* satisfy the trait binding. If it would, suggest calling
910 /// it: `bar(foo)` → `bar(foo())`. This case is *very* likely to be hit if `foo` is `async`.
suggest_fn_call( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool911 fn suggest_fn_call(
912 &self,
913 obligation: &PredicateObligation<'tcx>,
914 err: &mut Diagnostic,
915 trait_pred: ty::PolyTraitPredicate<'tcx>,
916 ) -> bool {
917 // It doesn't make sense to make this suggestion outside of typeck...
918 // (also autoderef will ICE...)
919 if self.typeck_results.is_none() {
920 return false;
921 }
922
923 if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) = obligation.predicate.kind().skip_binder()
924 && Some(trait_pred.def_id()) == self.tcx.lang_items().sized_trait()
925 {
926 // Don't suggest calling to turn an unsized type into a sized type
927 return false;
928 }
929
930 let self_ty = self.instantiate_binder_with_fresh_vars(
931 DUMMY_SP,
932 LateBoundRegionConversionTime::FnCall,
933 trait_pred.self_ty(),
934 );
935
936 let Some((def_id_or_name, output, inputs)) = self.extract_callable_info(
937 obligation.cause.body_id,
938 obligation.param_env,
939 self_ty,
940 ) else { return false; };
941
942 // Remapping bound vars here
943 let trait_pred_and_self = trait_pred.map_bound(|trait_pred| (trait_pred, output));
944
945 let new_obligation =
946 self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred_and_self);
947 if !self.predicate_must_hold_modulo_regions(&new_obligation) {
948 return false;
949 }
950
951 // Get the name of the callable and the arguments to be used in the suggestion.
952 let hir = self.tcx.hir();
953
954 let msg = match def_id_or_name {
955 DefIdOrName::DefId(def_id) => match self.tcx.def_kind(def_id) {
956 DefKind::Ctor(CtorOf::Struct, _) => {
957 Cow::from("use parentheses to construct this tuple struct")
958 }
959 DefKind::Ctor(CtorOf::Variant, _) => {
960 Cow::from("use parentheses to construct this tuple variant")
961 }
962 kind => Cow::from(format!(
963 "use parentheses to call this {}",
964 self.tcx.def_kind_descr(kind, def_id)
965 )),
966 },
967 DefIdOrName::Name(name) => Cow::from(format!("use parentheses to call this {name}")),
968 };
969
970 let args = inputs
971 .into_iter()
972 .map(|ty| {
973 if ty.is_suggestable(self.tcx, false) {
974 format!("/* {ty} */")
975 } else {
976 "/* value */".to_string()
977 }
978 })
979 .collect::<Vec<_>>()
980 .join(", ");
981
982 if matches!(obligation.cause.code(), ObligationCauseCode::FunctionArgumentObligation { .. })
983 && obligation.cause.span.can_be_used_for_suggestions()
984 {
985 // When the obligation error has been ensured to have been caused by
986 // an argument, the `obligation.cause.span` points at the expression
987 // of the argument, so we can provide a suggestion. Otherwise, we give
988 // a more general note.
989 err.span_suggestion_verbose(
990 obligation.cause.span.shrink_to_hi(),
991 msg,
992 format!("({args})"),
993 Applicability::HasPlaceholders,
994 );
995 } else if let DefIdOrName::DefId(def_id) = def_id_or_name {
996 let name = match hir.get_if_local(def_id) {
997 Some(hir::Node::Expr(hir::Expr {
998 kind: hir::ExprKind::Closure(hir::Closure { fn_decl_span, .. }),
999 ..
1000 })) => {
1001 err.span_label(*fn_decl_span, "consider calling this closure");
1002 let Some(name) = self.get_closure_name(def_id, err, msg.clone()) else {
1003 return false;
1004 };
1005 name.to_string()
1006 }
1007 Some(hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(..), .. })) => {
1008 err.span_label(ident.span, "consider calling this function");
1009 ident.to_string()
1010 }
1011 Some(hir::Node::Ctor(..)) => {
1012 let name = self.tcx.def_path_str(def_id);
1013 err.span_label(
1014 self.tcx.def_span(def_id),
1015 format!("consider calling the constructor for `{}`", name),
1016 );
1017 name
1018 }
1019 _ => return false,
1020 };
1021 err.help(format!("{msg}: `{name}({args})`"));
1022 }
1023 true
1024 }
1025
check_for_binding_assigned_block_without_tail_expression( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )1026 fn check_for_binding_assigned_block_without_tail_expression(
1027 &self,
1028 obligation: &PredicateObligation<'tcx>,
1029 err: &mut Diagnostic,
1030 trait_pred: ty::PolyTraitPredicate<'tcx>,
1031 ) {
1032 let mut span = obligation.cause.span;
1033 while span.from_expansion() {
1034 // Remove all the desugaring and macro contexts.
1035 span.remove_mark();
1036 }
1037 let mut expr_finder = FindExprBySpan::new(span);
1038 let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else { return; };
1039 let body = self.tcx.hir().body(body_id);
1040 expr_finder.visit_expr(body.value);
1041 let Some(expr) = expr_finder.result else { return; };
1042 let Some(typeck) = &self.typeck_results else { return; };
1043 let Some(ty) = typeck.expr_ty_adjusted_opt(expr) else { return; };
1044 if !ty.is_unit() {
1045 return;
1046 };
1047 let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind else { return; };
1048 let hir::def::Res::Local(hir_id) = path.res else { return; };
1049 let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(hir_id) else {
1050 return;
1051 };
1052 let Some(hir::Node::Local(hir::Local {
1053 ty: None,
1054 init: Some(init),
1055 ..
1056 })) = self.tcx.hir().find_parent(pat.hir_id) else { return; };
1057 let hir::ExprKind::Block(block, None) = init.kind else { return; };
1058 if block.expr.is_some() {
1059 return;
1060 }
1061 let [.., stmt] = block.stmts else {
1062 err.span_label(block.span, "this empty block is missing a tail expression");
1063 return;
1064 };
1065 let hir::StmtKind::Semi(tail_expr) = stmt.kind else { return; };
1066 let Some(ty) = typeck.expr_ty_opt(tail_expr) else {
1067 err.span_label(block.span, "this block is missing a tail expression");
1068 return;
1069 };
1070 let ty = self.resolve_numeric_literals_with_default(self.resolve_vars_if_possible(ty));
1071 let trait_pred_and_self = trait_pred.map_bound(|trait_pred| (trait_pred, ty));
1072
1073 let new_obligation =
1074 self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred_and_self);
1075 if self.predicate_must_hold_modulo_regions(&new_obligation) {
1076 err.span_suggestion_short(
1077 stmt.span.with_lo(tail_expr.span.hi()),
1078 "remove this semicolon",
1079 "",
1080 Applicability::MachineApplicable,
1081 );
1082 } else {
1083 err.span_label(block.span, "this block is missing a tail expression");
1084 }
1085 }
1086
suggest_add_clone_to_arg( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool1087 fn suggest_add_clone_to_arg(
1088 &self,
1089 obligation: &PredicateObligation<'tcx>,
1090 err: &mut Diagnostic,
1091 trait_pred: ty::PolyTraitPredicate<'tcx>,
1092 ) -> bool {
1093 let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
1094 let ty = self.instantiate_binder_with_placeholders(self_ty);
1095 let Some(generics) = self.tcx.hir().get_generics(obligation.cause.body_id) else { return false };
1096 let ty::Ref(_, inner_ty, hir::Mutability::Not) = ty.kind() else { return false };
1097 let ty::Param(param) = inner_ty.kind() else { return false };
1098 let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, .. } = obligation.cause.code() else { return false };
1099 let arg_node = self.tcx.hir().get(*arg_hir_id);
1100 let Node::Expr(Expr { kind: hir::ExprKind::Path(_), ..}) = arg_node else { return false };
1101
1102 let clone_trait = self.tcx.require_lang_item(LangItem::Clone, None);
1103 let has_clone = |ty| {
1104 self.type_implements_trait(clone_trait, [ty], obligation.param_env)
1105 .must_apply_modulo_regions()
1106 };
1107
1108 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1109 obligation.param_env,
1110 trait_pred.map_bound(|trait_pred| (trait_pred, *inner_ty)),
1111 );
1112
1113 if self.predicate_may_hold(&new_obligation) && has_clone(ty) {
1114 if !has_clone(param.to_ty(self.tcx)) {
1115 suggest_constraining_type_param(
1116 self.tcx,
1117 generics,
1118 err,
1119 param.name.as_str(),
1120 "Clone",
1121 Some(clone_trait),
1122 None,
1123 );
1124 }
1125 err.span_suggestion_verbose(
1126 obligation.cause.span.shrink_to_hi(),
1127 "consider using clone here",
1128 ".clone()".to_string(),
1129 Applicability::MaybeIncorrect,
1130 );
1131 return true;
1132 }
1133 false
1134 }
1135
1136 /// Extracts information about a callable type for diagnostics. This is a
1137 /// heuristic -- it doesn't necessarily mean that a type is always callable,
1138 /// because the callable type must also be well-formed to be called.
extract_callable_info( &self, body_id: LocalDefId, param_env: ty::ParamEnv<'tcx>, found: Ty<'tcx>, ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)>1139 fn extract_callable_info(
1140 &self,
1141 body_id: LocalDefId,
1142 param_env: ty::ParamEnv<'tcx>,
1143 found: Ty<'tcx>,
1144 ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)> {
1145 // Autoderef is useful here because sometimes we box callables, etc.
1146 let Some((def_id_or_name, output, inputs)) = (self.autoderef_steps)(found).into_iter().find_map(|(found, _)| {
1147 match *found.kind() {
1148 ty::FnPtr(fn_sig) =>
1149 Some((DefIdOrName::Name("function pointer"), fn_sig.output(), fn_sig.inputs())),
1150 ty::FnDef(def_id, _) => {
1151 let fn_sig = found.fn_sig(self.tcx);
1152 Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs()))
1153 }
1154 ty::Closure(def_id, substs) => {
1155 let fn_sig = substs.as_closure().sig();
1156 Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs().map_bound(|inputs| &inputs[1..])))
1157 }
1158 ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
1159 self.tcx.item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
1160 if let ty::ClauseKind::Projection(proj) = pred.kind().skip_binder()
1161 && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
1162 // args tuple will always be substs[1]
1163 && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
1164 {
1165 Some((
1166 DefIdOrName::DefId(def_id),
1167 pred.kind().rebind(proj.term.ty().unwrap()),
1168 pred.kind().rebind(args.as_slice()),
1169 ))
1170 } else {
1171 None
1172 }
1173 })
1174 }
1175 ty::Dynamic(data, _, ty::Dyn) => {
1176 data.iter().find_map(|pred| {
1177 if let ty::ExistentialPredicate::Projection(proj) = pred.skip_binder()
1178 && Some(proj.def_id) == self.tcx.lang_items().fn_once_output()
1179 // for existential projection, substs are shifted over by 1
1180 && let ty::Tuple(args) = proj.substs.type_at(0).kind()
1181 {
1182 Some((
1183 DefIdOrName::Name("trait object"),
1184 pred.rebind(proj.term.ty().unwrap()),
1185 pred.rebind(args.as_slice()),
1186 ))
1187 } else {
1188 None
1189 }
1190 })
1191 }
1192 ty::Param(param) => {
1193 let generics = self.tcx.generics_of(body_id);
1194 let name = if generics.count() > param.index as usize
1195 && let def = generics.param_at(param.index as usize, self.tcx)
1196 && matches!(def.kind, ty::GenericParamDefKind::Type { .. })
1197 && def.name == param.name
1198 {
1199 DefIdOrName::DefId(def.def_id)
1200 } else {
1201 DefIdOrName::Name("type parameter")
1202 };
1203 param_env.caller_bounds().iter().find_map(|pred| {
1204 if let ty::ClauseKind::Projection(proj) = pred.kind().skip_binder()
1205 && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
1206 && proj.projection_ty.self_ty() == found
1207 // args tuple will always be substs[1]
1208 && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
1209 {
1210 Some((
1211 name,
1212 pred.kind().rebind(proj.term.ty().unwrap()),
1213 pred.kind().rebind(args.as_slice()),
1214 ))
1215 } else {
1216 None
1217 }
1218 })
1219 }
1220 _ => None,
1221 }
1222 }) else { return None; };
1223
1224 let output = self.instantiate_binder_with_fresh_vars(
1225 DUMMY_SP,
1226 LateBoundRegionConversionTime::FnCall,
1227 output,
1228 );
1229 let inputs = inputs
1230 .skip_binder()
1231 .iter()
1232 .map(|ty| {
1233 self.instantiate_binder_with_fresh_vars(
1234 DUMMY_SP,
1235 LateBoundRegionConversionTime::FnCall,
1236 inputs.rebind(*ty),
1237 )
1238 })
1239 .collect();
1240
1241 // We don't want to register any extra obligations, which should be
1242 // implied by wf, but also because that would possibly result in
1243 // erroneous errors later on.
1244 let InferOk { value: output, obligations: _ } =
1245 self.at(&ObligationCause::dummy(), param_env).normalize(output);
1246
1247 if output.is_ty_var() { None } else { Some((def_id_or_name, output, inputs)) }
1248 }
1249
suggest_add_reference_to_arg( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, poly_trait_pred: ty::PolyTraitPredicate<'tcx>, has_custom_message: bool, ) -> bool1250 fn suggest_add_reference_to_arg(
1251 &self,
1252 obligation: &PredicateObligation<'tcx>,
1253 err: &mut Diagnostic,
1254 poly_trait_pred: ty::PolyTraitPredicate<'tcx>,
1255 has_custom_message: bool,
1256 ) -> bool {
1257 let span = obligation.cause.span;
1258
1259 let code = if let ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } =
1260 obligation.cause.code()
1261 {
1262 &parent_code
1263 } else if let ObligationCauseCode::ItemObligation(_)
1264 | ObligationCauseCode::ExprItemObligation(..) = obligation.cause.code()
1265 {
1266 obligation.cause.code()
1267 } else if let ExpnKind::Desugaring(DesugaringKind::ForLoop) =
1268 span.ctxt().outer_expn_data().kind
1269 {
1270 obligation.cause.code()
1271 } else {
1272 return false;
1273 };
1274
1275 // List of traits for which it would be nonsensical to suggest borrowing.
1276 // For instance, immutable references are always Copy, so suggesting to
1277 // borrow would always succeed, but it's probably not what the user wanted.
1278 let mut never_suggest_borrow: Vec<_> =
1279 [LangItem::Copy, LangItem::Clone, LangItem::Unpin, LangItem::Sized]
1280 .iter()
1281 .filter_map(|lang_item| self.tcx.lang_items().get(*lang_item))
1282 .collect();
1283
1284 if let Some(def_id) = self.tcx.get_diagnostic_item(sym::Send) {
1285 never_suggest_borrow.push(def_id);
1286 }
1287
1288 let param_env = obligation.param_env;
1289
1290 // Try to apply the original trait binding obligation by borrowing.
1291 let mut try_borrowing = |old_pred: ty::PolyTraitPredicate<'tcx>,
1292 blacklist: &[DefId]|
1293 -> bool {
1294 if blacklist.contains(&old_pred.def_id()) {
1295 return false;
1296 }
1297 // We map bounds to `&T` and `&mut T`
1298 let trait_pred_and_imm_ref = old_pred.map_bound(|trait_pred| {
1299 (
1300 trait_pred,
1301 Ty::new_imm_ref(self.tcx, self.tcx.lifetimes.re_static, trait_pred.self_ty()),
1302 )
1303 });
1304 let trait_pred_and_mut_ref = old_pred.map_bound(|trait_pred| {
1305 (
1306 trait_pred,
1307 Ty::new_mut_ref(self.tcx, self.tcx.lifetimes.re_static, trait_pred.self_ty()),
1308 )
1309 });
1310
1311 let mk_result = |trait_pred_and_new_ty| {
1312 let obligation =
1313 self.mk_trait_obligation_with_new_self_ty(param_env, trait_pred_and_new_ty);
1314 self.predicate_must_hold_modulo_regions(&obligation)
1315 };
1316 let imm_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_imm_ref);
1317 let mut_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_mut_ref);
1318
1319 let (ref_inner_ty_satisfies_pred, ref_inner_ty_mut) =
1320 if let ObligationCauseCode::ItemObligation(_) | ObligationCauseCode::ExprItemObligation(..) = obligation.cause.code()
1321 && let ty::Ref(_, ty, mutability) = old_pred.self_ty().skip_binder().kind()
1322 {
1323 (
1324 mk_result(old_pred.map_bound(|trait_pred| (trait_pred, *ty))),
1325 mutability.is_mut(),
1326 )
1327 } else {
1328 (false, false)
1329 };
1330
1331 if imm_ref_self_ty_satisfies_pred
1332 || mut_ref_self_ty_satisfies_pred
1333 || ref_inner_ty_satisfies_pred
1334 {
1335 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1336 // We don't want a borrowing suggestion on the fields in structs,
1337 // ```
1338 // struct Foo {
1339 // the_foos: Vec<Foo>
1340 // }
1341 // ```
1342 if !matches!(
1343 span.ctxt().outer_expn_data().kind,
1344 ExpnKind::Root | ExpnKind::Desugaring(DesugaringKind::ForLoop)
1345 ) {
1346 return false;
1347 }
1348 if snippet.starts_with('&') {
1349 // This is already a literal borrow and the obligation is failing
1350 // somewhere else in the obligation chain. Do not suggest non-sense.
1351 return false;
1352 }
1353 // We have a very specific type of error, where just borrowing this argument
1354 // might solve the problem. In cases like this, the important part is the
1355 // original type obligation, not the last one that failed, which is arbitrary.
1356 // Because of this, we modify the error to refer to the original obligation and
1357 // return early in the caller.
1358
1359 let msg = format!("the trait bound `{}` is not satisfied", old_pred);
1360 if has_custom_message {
1361 err.note(msg);
1362 } else {
1363 err.message =
1364 vec![(rustc_errors::DiagnosticMessage::from(msg), Style::NoStyle)];
1365 }
1366 err.span_label(
1367 span,
1368 format!(
1369 "the trait `{}` is not implemented for `{}`",
1370 old_pred.print_modifiers_and_trait_path(),
1371 old_pred.self_ty().skip_binder(),
1372 ),
1373 );
1374
1375 if imm_ref_self_ty_satisfies_pred && mut_ref_self_ty_satisfies_pred {
1376 err.span_suggestions(
1377 span.shrink_to_lo(),
1378 "consider borrowing here",
1379 ["&".to_string(), "&mut ".to_string()],
1380 Applicability::MaybeIncorrect,
1381 );
1382 } else {
1383 let is_mut = mut_ref_self_ty_satisfies_pred || ref_inner_ty_mut;
1384 let sugg_prefix = format!("&{}", if is_mut { "mut " } else { "" });
1385 let sugg_msg = format!(
1386 "consider{} borrowing here",
1387 if is_mut { " mutably" } else { "" }
1388 );
1389
1390 // Issue #109436, we need to add parentheses properly for method calls
1391 // for example, `foo.into()` should be `(&foo).into()`
1392 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(
1393 self.tcx.sess.source_map().span_look_ahead(span, Some("."), Some(50)),
1394 ) {
1395 if snippet == "." {
1396 err.multipart_suggestion_verbose(
1397 sugg_msg,
1398 vec![
1399 (span.shrink_to_lo(), format!("({}", sugg_prefix)),
1400 (span.shrink_to_hi(), ")".to_string()),
1401 ],
1402 Applicability::MaybeIncorrect,
1403 );
1404 return true;
1405 }
1406 }
1407
1408 // Issue #104961, we need to add parentheses properly for compound expressions
1409 // for example, `x.starts_with("hi".to_string() + "you")`
1410 // should be `x.starts_with(&("hi".to_string() + "you"))`
1411 let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else { return false; };
1412 let body = self.tcx.hir().body(body_id);
1413 let mut expr_finder = FindExprBySpan::new(span);
1414 expr_finder.visit_expr(body.value);
1415 let Some(expr) = expr_finder.result else { return false; };
1416 let needs_parens = match expr.kind {
1417 // parenthesize if needed (Issue #46756)
1418 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
1419 // parenthesize borrows of range literals (Issue #54505)
1420 _ if is_range_literal(expr) => true,
1421 _ => false,
1422 };
1423
1424 let span = if needs_parens { span } else { span.shrink_to_lo() };
1425 let suggestions = if !needs_parens {
1426 vec![(span.shrink_to_lo(), format!("{}", sugg_prefix))]
1427 } else {
1428 vec![
1429 (span.shrink_to_lo(), format!("{}(", sugg_prefix)),
1430 (span.shrink_to_hi(), ")".to_string()),
1431 ]
1432 };
1433 err.multipart_suggestion_verbose(
1434 sugg_msg,
1435 suggestions,
1436 Applicability::MaybeIncorrect,
1437 );
1438 }
1439 return true;
1440 }
1441 }
1442 return false;
1443 };
1444
1445 if let ObligationCauseCode::ImplDerivedObligation(cause) = &*code {
1446 try_borrowing(cause.derived.parent_trait_pred, &[])
1447 } else if let ObligationCauseCode::BindingObligation(_, _)
1448 | ObligationCauseCode::ItemObligation(_)
1449 | ObligationCauseCode::ExprItemObligation(..)
1450 | ObligationCauseCode::ExprBindingObligation(..) = code
1451 {
1452 try_borrowing(poly_trait_pred, &never_suggest_borrow)
1453 } else {
1454 false
1455 }
1456 }
1457
1458 // Suggest borrowing the type
suggest_borrowing_for_object_cast( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, self_ty: Ty<'tcx>, target_ty: Ty<'tcx>, )1459 fn suggest_borrowing_for_object_cast(
1460 &self,
1461 err: &mut Diagnostic,
1462 obligation: &PredicateObligation<'tcx>,
1463 self_ty: Ty<'tcx>,
1464 target_ty: Ty<'tcx>,
1465 ) {
1466 let ty::Ref(_, object_ty, hir::Mutability::Not) = target_ty.kind() else { return; };
1467 let ty::Dynamic(predicates, _, ty::Dyn) = object_ty.kind() else { return; };
1468 let self_ref_ty = Ty::new_imm_ref(self.tcx, self.tcx.lifetimes.re_erased, self_ty);
1469
1470 for predicate in predicates.iter() {
1471 if !self.predicate_must_hold_modulo_regions(
1472 &obligation.with(self.tcx, predicate.with_self_ty(self.tcx, self_ref_ty)),
1473 ) {
1474 return;
1475 }
1476 }
1477
1478 err.span_suggestion(
1479 obligation.cause.span.shrink_to_lo(),
1480 format!(
1481 "consider borrowing the value, since `&{self_ty}` can be coerced into `{target_ty}`"
1482 ),
1483 "&",
1484 Applicability::MaybeIncorrect,
1485 );
1486 }
1487
1488 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1489 /// suggest removing these references until we reach a type that implements the trait.
suggest_remove_reference( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool1490 fn suggest_remove_reference(
1491 &self,
1492 obligation: &PredicateObligation<'tcx>,
1493 err: &mut Diagnostic,
1494 trait_pred: ty::PolyTraitPredicate<'tcx>,
1495 ) -> bool {
1496 let mut span = obligation.cause.span;
1497 let mut trait_pred = trait_pred;
1498 let mut code = obligation.cause.code();
1499 while let Some((c, Some(parent_trait_pred))) = code.parent() {
1500 // We want the root obligation, in order to detect properly handle
1501 // `for _ in &mut &mut vec![] {}`.
1502 code = c;
1503 trait_pred = parent_trait_pred;
1504 }
1505 while span.desugaring_kind().is_some() {
1506 // Remove all the hir desugaring contexts while maintaining the macro contexts.
1507 span.remove_mark();
1508 }
1509 let mut expr_finder = super::FindExprBySpan::new(span);
1510 let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else {
1511 return false;
1512 };
1513 let body = self.tcx.hir().body(body_id);
1514 expr_finder.visit_expr(body.value);
1515 let mut maybe_suggest = |suggested_ty, count, suggestions| {
1516 // Remapping bound vars here
1517 let trait_pred_and_suggested_ty =
1518 trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty));
1519
1520 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1521 obligation.param_env,
1522 trait_pred_and_suggested_ty,
1523 );
1524
1525 if self.predicate_may_hold(&new_obligation) {
1526 let msg = if count == 1 {
1527 "consider removing the leading `&`-reference".to_string()
1528 } else {
1529 format!("consider removing {count} leading `&`-references")
1530 };
1531
1532 err.multipart_suggestion_verbose(
1533 msg,
1534 suggestions,
1535 Applicability::MachineApplicable,
1536 );
1537 true
1538 } else {
1539 false
1540 }
1541 };
1542
1543 // Maybe suggest removal of borrows from types in type parameters, like in
1544 // `src/test/ui/not-panic/not-panic-safe.rs`.
1545 let mut count = 0;
1546 let mut suggestions = vec![];
1547 // Skipping binder here, remapping below
1548 let mut suggested_ty = trait_pred.self_ty().skip_binder();
1549 if let Some(mut hir_ty) = expr_finder.ty_result {
1550 while let hir::TyKind::Ref(_, mut_ty) = &hir_ty.kind {
1551 count += 1;
1552 let span = hir_ty.span.until(mut_ty.ty.span);
1553 suggestions.push((span, String::new()));
1554
1555 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
1556 break;
1557 };
1558 suggested_ty = *inner_ty;
1559
1560 hir_ty = mut_ty.ty;
1561
1562 if maybe_suggest(suggested_ty, count, suggestions.clone()) {
1563 return true;
1564 }
1565 }
1566 }
1567
1568 // Maybe suggest removal of borrows from expressions, like in `for i in &&&foo {}`.
1569 let Some(mut expr) = expr_finder.result else { return false; };
1570 let mut count = 0;
1571 let mut suggestions = vec![];
1572 // Skipping binder here, remapping below
1573 let mut suggested_ty = trait_pred.self_ty().skip_binder();
1574 'outer: loop {
1575 while let hir::ExprKind::AddrOf(_, _, borrowed) = expr.kind {
1576 count += 1;
1577 let span = if expr.span.eq_ctxt(borrowed.span) {
1578 expr.span.until(borrowed.span)
1579 } else {
1580 expr.span.with_hi(expr.span.lo() + BytePos(1))
1581 };
1582 suggestions.push((span, String::new()));
1583
1584 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
1585 break 'outer;
1586 };
1587 suggested_ty = *inner_ty;
1588
1589 expr = borrowed;
1590
1591 if maybe_suggest(suggested_ty, count, suggestions.clone()) {
1592 return true;
1593 }
1594 }
1595 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
1596 && let hir::def::Res::Local(hir_id) = path.res
1597 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(hir_id)
1598 && let Some(hir::Node::Local(local)) = self.tcx.hir().find_parent(binding.hir_id)
1599 && let None = local.ty
1600 && let Some(binding_expr) = local.init
1601 {
1602 expr = binding_expr;
1603 } else {
1604 break 'outer;
1605 }
1606 }
1607 false
1608 }
1609
suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic)1610 fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic) {
1611 let hir = self.tcx.hir();
1612 if let ObligationCauseCode::AwaitableExpr(Some(hir_id)) = obligation.cause.code().peel_derives()
1613 && let hir::Node::Expr(expr) = hir.get(*hir_id)
1614 {
1615 // FIXME: use `obligation.predicate.kind()...trait_ref.self_ty()` to see if we have `()`
1616 // and if not maybe suggest doing something else? If we kept the expression around we
1617 // could also check if it is an fn call (very likely) and suggest changing *that*, if
1618 // it is from the local crate.
1619
1620 // use nth(1) to skip one layer of desugaring from `IntoIter::into_iter`
1621 if let Some((_, hir::Node::Expr(await_expr))) = hir.parent_iter(*hir_id).nth(1)
1622 && let Some(expr_span) = expr.span.find_ancestor_inside(await_expr.span)
1623 {
1624 let removal_span = self.tcx
1625 .sess
1626 .source_map()
1627 .span_extend_while(expr_span, char::is_whitespace)
1628 .unwrap_or(expr_span)
1629 .shrink_to_hi()
1630 .to(await_expr.span.shrink_to_hi());
1631 err.span_suggestion(
1632 removal_span,
1633 "remove the `.await`",
1634 "",
1635 Applicability::MachineApplicable,
1636 );
1637 } else {
1638 err.span_label(obligation.cause.span, "remove the `.await`");
1639 }
1640 // FIXME: account for associated `async fn`s.
1641 if let hir::Expr { span, kind: hir::ExprKind::Call(base, _), .. } = expr {
1642 if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
1643 obligation.predicate.kind().skip_binder()
1644 {
1645 err.span_label(*span, format!("this call returns `{}`", pred.self_ty()));
1646 }
1647 if let Some(typeck_results) = &self.typeck_results
1648 && let ty = typeck_results.expr_ty_adjusted(base)
1649 && let ty::FnDef(def_id, _substs) = ty.kind()
1650 && let Some(hir::Node::Item(hir::Item { ident, span, vis_span, .. })) =
1651 hir.get_if_local(*def_id)
1652 {
1653 let msg = format!(
1654 "alternatively, consider making `fn {}` asynchronous",
1655 ident
1656 );
1657 if vis_span.is_empty() {
1658 err.span_suggestion_verbose(
1659 span.shrink_to_lo(),
1660 msg,
1661 "async ",
1662 Applicability::MaybeIncorrect,
1663 );
1664 } else {
1665 err.span_suggestion_verbose(
1666 vis_span.shrink_to_hi(),
1667 msg,
1668 " async",
1669 Applicability::MaybeIncorrect,
1670 );
1671 }
1672 }
1673 }
1674 }
1675 }
1676
1677 /// Check if the trait bound is implemented for a different mutability and note it in the
1678 /// final error.
suggest_change_mut( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )1679 fn suggest_change_mut(
1680 &self,
1681 obligation: &PredicateObligation<'tcx>,
1682 err: &mut Diagnostic,
1683 trait_pred: ty::PolyTraitPredicate<'tcx>,
1684 ) {
1685 let points_at_arg = matches!(
1686 obligation.cause.code(),
1687 ObligationCauseCode::FunctionArgumentObligation { .. },
1688 );
1689
1690 let span = obligation.cause.span;
1691 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1692 let refs_number =
1693 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
1694 if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) {
1695 // Do not suggest removal of borrow from type arguments.
1696 return;
1697 }
1698 let trait_pred = self.resolve_vars_if_possible(trait_pred);
1699 if trait_pred.has_non_region_infer() {
1700 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1701 // unresolved bindings.
1702 return;
1703 }
1704
1705 // Skipping binder here, remapping below
1706 if let ty::Ref(region, t_type, mutability) = *trait_pred.skip_binder().self_ty().kind()
1707 {
1708 let suggested_ty = match mutability {
1709 hir::Mutability::Mut => Ty::new_imm_ref(self.tcx, region, t_type),
1710 hir::Mutability::Not => Ty::new_mut_ref(self.tcx, region, t_type),
1711 };
1712
1713 // Remapping bound vars here
1714 let trait_pred_and_suggested_ty =
1715 trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty));
1716
1717 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1718 obligation.param_env,
1719 trait_pred_and_suggested_ty,
1720 );
1721 let suggested_ty_would_satisfy_obligation = self
1722 .evaluate_obligation_no_overflow(&new_obligation)
1723 .must_apply_modulo_regions();
1724 if suggested_ty_would_satisfy_obligation {
1725 let sp = self
1726 .tcx
1727 .sess
1728 .source_map()
1729 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1730 if points_at_arg && mutability.is_not() && refs_number > 0 {
1731 // If we have a call like foo(&mut buf), then don't suggest foo(&mut mut buf)
1732 if snippet
1733 .trim_start_matches(|c: char| c.is_whitespace() || c == '&')
1734 .starts_with("mut")
1735 {
1736 return;
1737 }
1738 err.span_suggestion_verbose(
1739 sp,
1740 "consider changing this borrow's mutability",
1741 "&mut ",
1742 Applicability::MachineApplicable,
1743 );
1744 } else {
1745 err.note(format!(
1746 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1747 trait_pred.print_modifiers_and_trait_path(),
1748 suggested_ty,
1749 trait_pred.skip_binder().self_ty(),
1750 ));
1751 }
1752 }
1753 }
1754 }
1755 }
1756
suggest_semicolon_removal( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, span: Span, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool1757 fn suggest_semicolon_removal(
1758 &self,
1759 obligation: &PredicateObligation<'tcx>,
1760 err: &mut Diagnostic,
1761 span: Span,
1762 trait_pred: ty::PolyTraitPredicate<'tcx>,
1763 ) -> bool {
1764 let hir = self.tcx.hir();
1765 let node = hir.find_by_def_id(obligation.cause.body_id);
1766 if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. })) = node
1767 && let hir::ExprKind::Block(blk, _) = &hir.body(*body_id).value.kind
1768 && sig.decl.output.span().overlaps(span)
1769 && blk.expr.is_none()
1770 && trait_pred.self_ty().skip_binder().is_unit()
1771 && let Some(stmt) = blk.stmts.last()
1772 && let hir::StmtKind::Semi(expr) = stmt.kind
1773 // Only suggest this if the expression behind the semicolon implements the predicate
1774 && let Some(typeck_results) = &self.typeck_results
1775 && let Some(ty) = typeck_results.expr_ty_opt(expr)
1776 && self.predicate_may_hold(&self.mk_trait_obligation_with_new_self_ty(
1777 obligation.param_env, trait_pred.map_bound(|trait_pred| (trait_pred, ty))
1778 ))
1779 {
1780 err.span_label(
1781 expr.span,
1782 format!(
1783 "this expression has type `{}`, which implements `{}`",
1784 ty,
1785 trait_pred.print_modifiers_and_trait_path()
1786 )
1787 );
1788 err.span_suggestion(
1789 self.tcx.sess.source_map().end_point(stmt.span),
1790 "remove this semicolon",
1791 "",
1792 Applicability::MachineApplicable
1793 );
1794 return true;
1795 }
1796 false
1797 }
1798
return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>1799 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span> {
1800 let hir = self.tcx.hir();
1801 let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })) = hir.find_by_def_id(obligation.cause.body_id) else {
1802 return None;
1803 };
1804
1805 if let hir::FnRetTy::Return(ret_ty) = sig.decl.output { Some(ret_ty.span) } else { None }
1806 }
1807
1808 /// If all conditions are met to identify a returned `dyn Trait`, suggest using `impl Trait` if
1809 /// applicable and signal that the error has been expanded appropriately and needs to be
1810 /// emitted.
suggest_impl_trait( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, trait_pred: ty::PolyTraitPredicate<'tcx>, ) -> bool1811 fn suggest_impl_trait(
1812 &self,
1813 err: &mut Diagnostic,
1814 obligation: &PredicateObligation<'tcx>,
1815 trait_pred: ty::PolyTraitPredicate<'tcx>,
1816 ) -> bool {
1817 let ObligationCauseCode::SizedReturnType = obligation.cause.code() else {
1818 return false;
1819 };
1820 let ty::Dynamic(_, _, ty::Dyn) = trait_pred.self_ty().skip_binder().kind() else {
1821 return false;
1822 };
1823
1824 err.code(error_code!(E0746));
1825 err.set_primary_message("return type cannot have an unboxed trait object");
1826 err.children.clear();
1827
1828 let span = obligation.cause.span;
1829 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span)
1830 && snip.starts_with("dyn ")
1831 {
1832 err.span_suggestion(
1833 span.with_hi(span.lo() + BytePos(4)),
1834 "return an `impl Trait` instead of a `dyn Trait`, \
1835 if all returned values are the same type",
1836 "impl ",
1837 Applicability::MaybeIncorrect,
1838 );
1839 }
1840
1841 let body = self.tcx.hir().body(self.tcx.hir().body_owned_by(obligation.cause.body_id));
1842
1843 let mut visitor = ReturnsVisitor::default();
1844 visitor.visit_body(&body);
1845
1846 let mut sugg =
1847 vec![(span.shrink_to_lo(), "Box<".to_string()), (span.shrink_to_hi(), ">".to_string())];
1848 sugg.extend(visitor.returns.into_iter().flat_map(|expr| {
1849 let span = expr.span.find_ancestor_in_same_ctxt(obligation.cause.span).unwrap_or(expr.span);
1850 if !span.can_be_used_for_suggestions() {
1851 vec![]
1852 } else if let hir::ExprKind::Call(path, ..) = expr.kind
1853 && let hir::ExprKind::Path(hir::QPath::TypeRelative(ty, method)) = path.kind
1854 && method.ident.name == sym::new
1855 && let hir::TyKind::Path(hir::QPath::Resolved(.., box_path)) = ty.kind
1856 && box_path.res.opt_def_id().is_some_and(|def_id| Some(def_id) == self.tcx.lang_items().owned_box())
1857 {
1858 // Don't box `Box::new`
1859 vec![]
1860 } else {
1861 vec![
1862 (span.shrink_to_lo(), "Box::new(".to_string()),
1863 (span.shrink_to_hi(), ")".to_string()),
1864 ]
1865 }
1866 }));
1867
1868 err.multipart_suggestion(
1869 "box the return type, and wrap all of the returned values in `Box::new`",
1870 sugg,
1871 Applicability::MaybeIncorrect,
1872 );
1873
1874 true
1875 }
1876
point_at_returns_when_relevant( &self, err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>, obligation: &PredicateObligation<'tcx>, )1877 fn point_at_returns_when_relevant(
1878 &self,
1879 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1880 obligation: &PredicateObligation<'tcx>,
1881 ) {
1882 match obligation.cause.code().peel_derives() {
1883 ObligationCauseCode::SizedReturnType => {}
1884 _ => return,
1885 }
1886
1887 let hir = self.tcx.hir();
1888 let node = hir.find_by_def_id(obligation.cause.body_id);
1889 if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })) =
1890 node
1891 {
1892 let body = hir.body(*body_id);
1893 // Point at all the `return`s in the function as they have failed trait bounds.
1894 let mut visitor = ReturnsVisitor::default();
1895 visitor.visit_body(&body);
1896 let typeck_results = self.typeck_results.as_ref().unwrap();
1897 for expr in &visitor.returns {
1898 if let Some(returned_ty) = typeck_results.node_type_opt(expr.hir_id) {
1899 let ty = self.resolve_vars_if_possible(returned_ty);
1900 if ty.references_error() {
1901 // don't print out the [type error] here
1902 err.delay_as_bug();
1903 } else {
1904 err.span_label(
1905 expr.span,
1906 format!("this returned value is of type `{}`", ty),
1907 );
1908 }
1909 }
1910 }
1911 }
1912 }
1913
report_closure_arg_mismatch( &self, span: Span, found_span: Option<Span>, found: ty::PolyTraitRef<'tcx>, expected: ty::PolyTraitRef<'tcx>, cause: &ObligationCauseCode<'tcx>, found_node: Option<Node<'_>>, param_env: ty::ParamEnv<'tcx>, ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>1914 fn report_closure_arg_mismatch(
1915 &self,
1916 span: Span,
1917 found_span: Option<Span>,
1918 found: ty::PolyTraitRef<'tcx>,
1919 expected: ty::PolyTraitRef<'tcx>,
1920 cause: &ObligationCauseCode<'tcx>,
1921 found_node: Option<Node<'_>>,
1922 param_env: ty::ParamEnv<'tcx>,
1923 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1924 pub(crate) fn build_fn_sig_ty<'tcx>(
1925 infcx: &InferCtxt<'tcx>,
1926 trait_ref: ty::PolyTraitRef<'tcx>,
1927 ) -> Ty<'tcx> {
1928 let inputs = trait_ref.skip_binder().substs.type_at(1);
1929 let sig = match inputs.kind() {
1930 ty::Tuple(inputs) if infcx.tcx.is_fn_trait(trait_ref.def_id()) => {
1931 infcx.tcx.mk_fn_sig(
1932 *inputs,
1933 infcx.next_ty_var(TypeVariableOrigin {
1934 span: DUMMY_SP,
1935 kind: TypeVariableOriginKind::MiscVariable,
1936 }),
1937 false,
1938 hir::Unsafety::Normal,
1939 abi::Abi::Rust,
1940 )
1941 }
1942 _ => infcx.tcx.mk_fn_sig(
1943 [inputs],
1944 infcx.next_ty_var(TypeVariableOrigin {
1945 span: DUMMY_SP,
1946 kind: TypeVariableOriginKind::MiscVariable,
1947 }),
1948 false,
1949 hir::Unsafety::Normal,
1950 abi::Abi::Rust,
1951 ),
1952 };
1953
1954 Ty::new_fn_ptr(infcx.tcx, trait_ref.rebind(sig))
1955 }
1956
1957 let argument_kind = match expected.skip_binder().self_ty().kind() {
1958 ty::Closure(..) => "closure",
1959 ty::Generator(..) => "generator",
1960 _ => "function",
1961 };
1962 let mut err = struct_span_err!(
1963 self.tcx.sess,
1964 span,
1965 E0631,
1966 "type mismatch in {argument_kind} arguments",
1967 );
1968
1969 err.span_label(span, "expected due to this");
1970
1971 let found_span = found_span.unwrap_or(span);
1972 err.span_label(found_span, "found signature defined here");
1973
1974 let expected = build_fn_sig_ty(self, expected);
1975 let found = build_fn_sig_ty(self, found);
1976
1977 let (expected_str, found_str) = self.cmp(expected, found);
1978
1979 let signature_kind = format!("{argument_kind} signature");
1980 err.note_expected_found(&signature_kind, expected_str, &signature_kind, found_str);
1981
1982 self.note_conflicting_closure_bounds(cause, &mut err);
1983
1984 if let Some(found_node) = found_node {
1985 hint_missing_borrow(self, param_env, span, found, expected, found_node, &mut err);
1986 }
1987
1988 err
1989 }
1990
1991 // Add a note if there are two `Fn`-family bounds that have conflicting argument
1992 // requirements, which will always cause a closure to have a type error.
note_conflicting_closure_bounds( &self, cause: &ObligationCauseCode<'tcx>, err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>, )1993 fn note_conflicting_closure_bounds(
1994 &self,
1995 cause: &ObligationCauseCode<'tcx>,
1996 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1997 ) {
1998 // First, look for an `ExprBindingObligation`, which means we can get
1999 // the unsubstituted predicate list of the called function. And check
2000 // that the predicate that we failed to satisfy is a `Fn`-like trait.
2001 if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = cause
2002 && let predicates = self.tcx.predicates_of(def_id).instantiate_identity(self.tcx)
2003 && let Some(pred) = predicates.predicates.get(*idx)
2004 && let ty::ClauseKind::Trait(trait_pred) = pred.kind().skip_binder()
2005 && self.tcx.is_fn_trait(trait_pred.def_id())
2006 {
2007 let expected_self =
2008 self.tcx.anonymize_bound_vars(pred.kind().rebind(trait_pred.self_ty()));
2009 let expected_substs = self
2010 .tcx
2011 .anonymize_bound_vars(pred.kind().rebind(trait_pred.trait_ref.substs));
2012
2013 // Find another predicate whose self-type is equal to the expected self type,
2014 // but whose substs don't match.
2015 let other_pred = predicates.into_iter()
2016 .enumerate()
2017 .find(|(other_idx, (pred, _))| match pred.kind().skip_binder() {
2018 ty::ClauseKind::Trait(trait_pred)
2019 if self.tcx.is_fn_trait(trait_pred.def_id())
2020 && other_idx != idx
2021 // Make sure that the self type matches
2022 // (i.e. constraining this closure)
2023 && expected_self
2024 == self.tcx.anonymize_bound_vars(
2025 pred.kind().rebind(trait_pred.self_ty()),
2026 )
2027 // But the substs don't match (i.e. incompatible args)
2028 && expected_substs
2029 != self.tcx.anonymize_bound_vars(
2030 pred.kind().rebind(trait_pred.trait_ref.substs),
2031 ) =>
2032 {
2033 true
2034 }
2035 _ => false,
2036 });
2037 // If we found one, then it's very likely the cause of the error.
2038 if let Some((_, (_, other_pred_span))) = other_pred {
2039 err.span_note(
2040 other_pred_span,
2041 "closure inferred to have a different signature due to this bound",
2042 );
2043 }
2044 }
2045 }
2046
suggest_fully_qualified_path( &self, err: &mut Diagnostic, item_def_id: DefId, span: Span, trait_ref: DefId, )2047 fn suggest_fully_qualified_path(
2048 &self,
2049 err: &mut Diagnostic,
2050 item_def_id: DefId,
2051 span: Span,
2052 trait_ref: DefId,
2053 ) {
2054 if let Some(assoc_item) = self.tcx.opt_associated_item(item_def_id) {
2055 if let ty::AssocKind::Const | ty::AssocKind::Type = assoc_item.kind {
2056 err.note(format!(
2057 "{}s cannot be accessed directly on a `trait`, they can only be \
2058 accessed through a specific `impl`",
2059 self.tcx.def_kind_descr(assoc_item.kind.as_def_kind(), item_def_id)
2060 ));
2061 err.span_suggestion(
2062 span,
2063 "use the fully qualified path to an implementation",
2064 format!("<Type as {}>::{}", self.tcx.def_path_str(trait_ref), assoc_item.name),
2065 Applicability::HasPlaceholders,
2066 );
2067 }
2068 }
2069 }
2070
2071 /// Adds an async-await specific note to the diagnostic when the future does not implement
2072 /// an auto trait because of a captured type.
2073 ///
2074 /// ```text
2075 /// note: future does not implement `Qux` as this value is used across an await
2076 /// --> $DIR/issue-64130-3-other.rs:17:5
2077 /// |
2078 /// LL | let x = Foo;
2079 /// | - has type `Foo`
2080 /// LL | baz().await;
2081 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2082 /// LL | }
2083 /// | - `x` is later dropped here
2084 /// ```
2085 ///
2086 /// When the diagnostic does not implement `Send` or `Sync` specifically, then the diagnostic
2087 /// is "replaced" with a different message and a more specific error.
2088 ///
2089 /// ```text
2090 /// error: future cannot be sent between threads safely
2091 /// --> $DIR/issue-64130-2-send.rs:21:5
2092 /// |
2093 /// LL | fn is_send<T: Send>(t: T) { }
2094 /// | ---- required by this bound in `is_send`
2095 /// ...
2096 /// LL | is_send(bar());
2097 /// | ^^^^^^^ future returned by `bar` is not send
2098 /// |
2099 /// = help: within `impl std::future::Future`, the trait `std::marker::Send` is not
2100 /// implemented for `Foo`
2101 /// note: future is not send as this value is used across an await
2102 /// --> $DIR/issue-64130-2-send.rs:15:5
2103 /// |
2104 /// LL | let x = Foo;
2105 /// | - has type `Foo`
2106 /// LL | baz().await;
2107 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2108 /// LL | }
2109 /// | - `x` is later dropped here
2110 /// ```
2111 ///
2112 /// Returns `true` if an async-await specific note was added to the diagnostic.
2113 #[instrument(level = "debug", skip_all, fields(?obligation.predicate, ?obligation.cause.span))]
maybe_note_obligation_cause_for_async_await( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, ) -> bool2114 fn maybe_note_obligation_cause_for_async_await(
2115 &self,
2116 err: &mut Diagnostic,
2117 obligation: &PredicateObligation<'tcx>,
2118 ) -> bool {
2119 let hir = self.tcx.hir();
2120
2121 // Attempt to detect an async-await error by looking at the obligation causes, looking
2122 // for a generator to be present.
2123 //
2124 // When a future does not implement a trait because of a captured type in one of the
2125 // generators somewhere in the call stack, then the result is a chain of obligations.
2126 //
2127 // Given an `async fn` A that calls an `async fn` B which captures a non-send type and that
2128 // future is passed as an argument to a function C which requires a `Send` type, then the
2129 // chain looks something like this:
2130 //
2131 // - `BuiltinDerivedObligation` with a generator witness (B)
2132 // - `BuiltinDerivedObligation` with a generator (B)
2133 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2134 // - `BuiltinDerivedObligation` with a generator witness (A)
2135 // - `BuiltinDerivedObligation` with a generator (A)
2136 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2137 // - `BindingObligation` with `impl_send` (Send requirement)
2138 //
2139 // The first obligation in the chain is the most useful and has the generator that captured
2140 // the type. The last generator (`outer_generator` below) has information about where the
2141 // bound was introduced. At least one generator should be present for this diagnostic to be
2142 // modified.
2143 let (mut trait_ref, mut target_ty) = match obligation.predicate.kind().skip_binder() {
2144 ty::PredicateKind::Clause(ty::ClauseKind::Trait(p)) => (Some(p), Some(p.self_ty())),
2145 _ => (None, None),
2146 };
2147 let mut generator = None;
2148 let mut outer_generator = None;
2149 let mut next_code = Some(obligation.cause.code());
2150
2151 let mut seen_upvar_tys_infer_tuple = false;
2152
2153 while let Some(code) = next_code {
2154 debug!(?code);
2155 match code {
2156 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
2157 next_code = Some(parent_code);
2158 }
2159 ObligationCauseCode::ImplDerivedObligation(cause) => {
2160 let ty = cause.derived.parent_trait_pred.skip_binder().self_ty();
2161 debug!(
2162 parent_trait_ref = ?cause.derived.parent_trait_pred,
2163 self_ty.kind = ?ty.kind(),
2164 "ImplDerived",
2165 );
2166
2167 match *ty.kind() {
2168 ty::Generator(did, ..) | ty::GeneratorWitnessMIR(did, _) => {
2169 generator = generator.or(Some(did));
2170 outer_generator = Some(did);
2171 }
2172 ty::GeneratorWitness(..) => {}
2173 ty::Tuple(_) if !seen_upvar_tys_infer_tuple => {
2174 // By introducing a tuple of upvar types into the chain of obligations
2175 // of a generator, the first non-generator item is now the tuple itself,
2176 // we shall ignore this.
2177
2178 seen_upvar_tys_infer_tuple = true;
2179 }
2180 _ if generator.is_none() => {
2181 trait_ref = Some(cause.derived.parent_trait_pred.skip_binder());
2182 target_ty = Some(ty);
2183 }
2184 _ => {}
2185 }
2186
2187 next_code = Some(&cause.derived.parent_code);
2188 }
2189 ObligationCauseCode::DerivedObligation(derived_obligation)
2190 | ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) => {
2191 let ty = derived_obligation.parent_trait_pred.skip_binder().self_ty();
2192 debug!(
2193 parent_trait_ref = ?derived_obligation.parent_trait_pred,
2194 self_ty.kind = ?ty.kind(),
2195 );
2196
2197 match *ty.kind() {
2198 ty::Generator(did, ..) | ty::GeneratorWitnessMIR(did, ..) => {
2199 generator = generator.or(Some(did));
2200 outer_generator = Some(did);
2201 }
2202 ty::GeneratorWitness(..) => {}
2203 ty::Tuple(_) if !seen_upvar_tys_infer_tuple => {
2204 // By introducing a tuple of upvar types into the chain of obligations
2205 // of a generator, the first non-generator item is now the tuple itself,
2206 // we shall ignore this.
2207
2208 seen_upvar_tys_infer_tuple = true;
2209 }
2210 _ if generator.is_none() => {
2211 trait_ref = Some(derived_obligation.parent_trait_pred.skip_binder());
2212 target_ty = Some(ty);
2213 }
2214 _ => {}
2215 }
2216
2217 next_code = Some(&derived_obligation.parent_code);
2218 }
2219 _ => break,
2220 }
2221 }
2222
2223 // Only continue if a generator was found.
2224 debug!(?generator, ?trait_ref, ?target_ty);
2225 let (Some(generator_did), Some(trait_ref), Some(target_ty)) = (generator, trait_ref, target_ty) else {
2226 return false;
2227 };
2228
2229 let span = self.tcx.def_span(generator_did);
2230
2231 let generator_did_root = self.tcx.typeck_root_def_id(generator_did);
2232 debug!(
2233 ?generator_did,
2234 ?generator_did_root,
2235 typeck_results.hir_owner = ?self.typeck_results.as_ref().map(|t| t.hir_owner),
2236 ?span,
2237 );
2238
2239 let generator_body = generator_did
2240 .as_local()
2241 .and_then(|def_id| hir.maybe_body_owned_by(def_id))
2242 .map(|body_id| hir.body(body_id));
2243 let mut visitor = AwaitsVisitor::default();
2244 if let Some(body) = generator_body {
2245 visitor.visit_body(body);
2246 }
2247 debug!(awaits = ?visitor.awaits);
2248
2249 // Look for a type inside the generator interior that matches the target type to get
2250 // a span.
2251 let target_ty_erased = self.tcx.erase_regions(target_ty);
2252 let ty_matches = |ty| -> bool {
2253 // Careful: the regions for types that appear in the
2254 // generator interior are not generally known, so we
2255 // want to erase them when comparing (and anyway,
2256 // `Send` and other bounds are generally unaffected by
2257 // the choice of region). When erasing regions, we
2258 // also have to erase late-bound regions. This is
2259 // because the types that appear in the generator
2260 // interior generally contain "bound regions" to
2261 // represent regions that are part of the suspended
2262 // generator frame. Bound regions are preserved by
2263 // `erase_regions` and so we must also call
2264 // `erase_late_bound_regions`.
2265 let ty_erased = self.tcx.erase_late_bound_regions(ty);
2266 let ty_erased = self.tcx.erase_regions(ty_erased);
2267 let eq = ty_erased == target_ty_erased;
2268 debug!(?ty_erased, ?target_ty_erased, ?eq);
2269 eq
2270 };
2271
2272 // Get the typeck results from the infcx if the generator is the function we are currently
2273 // type-checking; otherwise, get them by performing a query. This is needed to avoid
2274 // cycles. If we can't use resolved types because the generator comes from another crate,
2275 // we still provide a targeted error but without all the relevant spans.
2276 let generator_data = match &self.typeck_results {
2277 Some(t) if t.hir_owner.to_def_id() == generator_did_root => GeneratorData::Local(&t),
2278 _ if generator_did.is_local() => {
2279 GeneratorData::Local(self.tcx.typeck(generator_did.expect_local()))
2280 }
2281 _ if let Some(generator_diag_data) = self.tcx.generator_diagnostic_data(generator_did) => {
2282 GeneratorData::Foreign(generator_diag_data)
2283 }
2284 _ => return false,
2285 };
2286
2287 let generator_within_in_progress_typeck = match &self.typeck_results {
2288 Some(t) => t.hir_owner.to_def_id() == generator_did_root,
2289 _ => false,
2290 };
2291
2292 let mut interior_or_upvar_span = None;
2293
2294 let from_awaited_ty = generator_data.get_from_await_ty(self.tcx, visitor, hir, ty_matches);
2295 debug!(?from_awaited_ty);
2296
2297 // The generator interior types share the same binders
2298 if let Some(cause) =
2299 generator_data.get_generator_interior_types().skip_binder().iter().find(
2300 |ty::GeneratorInteriorTypeCause { ty, .. }| {
2301 ty_matches(generator_data.get_generator_interior_types().rebind(*ty))
2302 },
2303 )
2304 {
2305 let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } = cause;
2306
2307 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(
2308 *span,
2309 Some((*scope_span, *yield_span, *expr, from_awaited_ty)),
2310 ));
2311
2312 if interior_or_upvar_span.is_none() && generator_data.is_foreign() {
2313 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(*span, None));
2314 }
2315 } else if self.tcx.sess.opts.unstable_opts.drop_tracking_mir
2316 // Avoid disclosing internal information to downstream crates.
2317 && generator_did.is_local()
2318 // Try to avoid cycles.
2319 && !generator_within_in_progress_typeck
2320 && let Some(generator_info) = self.tcx.mir_generator_witnesses(generator_did)
2321 {
2322 debug!(?generator_info);
2323 'find_source: for (variant, source_info) in
2324 generator_info.variant_fields.iter().zip(&generator_info.variant_source_info)
2325 {
2326 debug!(?variant);
2327 for &local in variant {
2328 let decl = &generator_info.field_tys[local];
2329 debug!(?decl);
2330 if ty_matches(ty::Binder::dummy(decl.ty)) && !decl.ignore_for_traits {
2331 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(
2332 decl.source_info.span,
2333 Some((None, source_info.span, None, from_awaited_ty)),
2334 ));
2335 break 'find_source;
2336 }
2337 }
2338 }
2339 }
2340
2341 if interior_or_upvar_span.is_none() {
2342 interior_or_upvar_span =
2343 generator_data.try_get_upvar_span(&self, generator_did, ty_matches);
2344 }
2345
2346 if interior_or_upvar_span.is_none() && generator_data.is_foreign() {
2347 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(span, None));
2348 }
2349
2350 debug!(?interior_or_upvar_span);
2351 if let Some(interior_or_upvar_span) = interior_or_upvar_span {
2352 let is_async = self.tcx.generator_is_async(generator_did);
2353 let typeck_results = match generator_data {
2354 GeneratorData::Local(typeck_results) => Some(typeck_results),
2355 GeneratorData::Foreign(_) => None,
2356 };
2357 self.note_obligation_cause_for_async_await(
2358 err,
2359 interior_or_upvar_span,
2360 is_async,
2361 outer_generator,
2362 trait_ref,
2363 target_ty,
2364 typeck_results,
2365 obligation,
2366 next_code,
2367 );
2368 true
2369 } else {
2370 false
2371 }
2372 }
2373
2374 /// Unconditionally adds the diagnostic note described in
2375 /// `maybe_note_obligation_cause_for_async_await`'s documentation comment.
2376 #[instrument(level = "debug", skip_all)]
note_obligation_cause_for_async_await( &self, err: &mut Diagnostic, interior_or_upvar_span: GeneratorInteriorOrUpvar, is_async: bool, outer_generator: Option<DefId>, trait_pred: ty::TraitPredicate<'tcx>, target_ty: Ty<'tcx>, typeck_results: Option<&ty::TypeckResults<'tcx>>, obligation: &PredicateObligation<'tcx>, next_code: Option<&ObligationCauseCode<'tcx>>, )2377 fn note_obligation_cause_for_async_await(
2378 &self,
2379 err: &mut Diagnostic,
2380 interior_or_upvar_span: GeneratorInteriorOrUpvar,
2381 is_async: bool,
2382 outer_generator: Option<DefId>,
2383 trait_pred: ty::TraitPredicate<'tcx>,
2384 target_ty: Ty<'tcx>,
2385 typeck_results: Option<&ty::TypeckResults<'tcx>>,
2386 obligation: &PredicateObligation<'tcx>,
2387 next_code: Option<&ObligationCauseCode<'tcx>>,
2388 ) {
2389 let source_map = self.tcx.sess.source_map();
2390
2391 let (await_or_yield, an_await_or_yield) =
2392 if is_async { ("await", "an await") } else { ("yield", "a yield") };
2393 let future_or_generator = if is_async { "future" } else { "generator" };
2394
2395 // Special case the primary error message when send or sync is the trait that was
2396 // not implemented.
2397 let hir = self.tcx.hir();
2398 let trait_explanation = if let Some(name @ (sym::Send | sym::Sync)) =
2399 self.tcx.get_diagnostic_name(trait_pred.def_id())
2400 {
2401 let (trait_name, trait_verb) =
2402 if name == sym::Send { ("`Send`", "sent") } else { ("`Sync`", "shared") };
2403
2404 err.clear_code();
2405 err.set_primary_message(format!(
2406 "{} cannot be {} between threads safely",
2407 future_or_generator, trait_verb
2408 ));
2409
2410 let original_span = err.span.primary_span().unwrap();
2411 let mut span = MultiSpan::from_span(original_span);
2412
2413 let message = outer_generator
2414 .and_then(|generator_did| {
2415 Some(match self.tcx.generator_kind(generator_did).unwrap() {
2416 GeneratorKind::Gen => format!("generator is not {}", trait_name),
2417 GeneratorKind::Async(AsyncGeneratorKind::Fn) => self
2418 .tcx
2419 .parent(generator_did)
2420 .as_local()
2421 .map(|parent_did| hir.local_def_id_to_hir_id(parent_did))
2422 .and_then(|parent_hir_id| hir.opt_name(parent_hir_id))
2423 .map(|name| {
2424 format!("future returned by `{}` is not {}", name, trait_name)
2425 })?,
2426 GeneratorKind::Async(AsyncGeneratorKind::Block) => {
2427 format!("future created by async block is not {}", trait_name)
2428 }
2429 GeneratorKind::Async(AsyncGeneratorKind::Closure) => {
2430 format!("future created by async closure is not {}", trait_name)
2431 }
2432 })
2433 })
2434 .unwrap_or_else(|| format!("{} is not {}", future_or_generator, trait_name));
2435
2436 span.push_span_label(original_span, message);
2437 err.set_span(span);
2438
2439 format!("is not {}", trait_name)
2440 } else {
2441 format!("does not implement `{}`", trait_pred.print_modifiers_and_trait_path())
2442 };
2443
2444 let mut explain_yield =
2445 |interior_span: Span, yield_span: Span, scope_span: Option<Span>| {
2446 let mut span = MultiSpan::from_span(yield_span);
2447 let snippet = match source_map.span_to_snippet(interior_span) {
2448 // #70935: If snippet contains newlines, display "the value" instead
2449 // so that we do not emit complex diagnostics.
2450 Ok(snippet) if !snippet.contains('\n') => format!("`{}`", snippet),
2451 _ => "the value".to_string(),
2452 };
2453 // note: future is not `Send` as this value is used across an await
2454 // --> $DIR/issue-70935-complex-spans.rs:13:9
2455 // |
2456 // LL | baz(|| async {
2457 // | ______________-
2458 // | |
2459 // | |
2460 // LL | | foo(tx.clone());
2461 // LL | | }).await;
2462 // | | - ^^^^^^ await occurs here, with value maybe used later
2463 // | |__________|
2464 // | has type `closure` which is not `Send`
2465 // note: value is later dropped here
2466 // LL | | }).await;
2467 // | | ^
2468 //
2469 span.push_span_label(
2470 yield_span,
2471 format!("{} occurs here, with {} maybe used later", await_or_yield, snippet),
2472 );
2473 span.push_span_label(
2474 interior_span,
2475 format!("has type `{}` which {}", target_ty, trait_explanation),
2476 );
2477 if let Some(scope_span) = scope_span {
2478 let scope_span = source_map.end_point(scope_span);
2479
2480 let msg = format!("{} is later dropped here", snippet);
2481 span.push_span_label(scope_span, msg);
2482 }
2483 err.span_note(
2484 span,
2485 format!(
2486 "{} {} as this value is used across {}",
2487 future_or_generator, trait_explanation, an_await_or_yield
2488 ),
2489 );
2490 };
2491 match interior_or_upvar_span {
2492 GeneratorInteriorOrUpvar::Interior(interior_span, interior_extra_info) => {
2493 if let Some((scope_span, yield_span, expr, from_awaited_ty)) = interior_extra_info {
2494 if let Some(await_span) = from_awaited_ty {
2495 // The type causing this obligation is one being awaited at await_span.
2496 let mut span = MultiSpan::from_span(await_span);
2497 span.push_span_label(
2498 await_span,
2499 format!(
2500 "await occurs here on type `{}`, which {}",
2501 target_ty, trait_explanation
2502 ),
2503 );
2504 err.span_note(
2505 span,
2506 format!(
2507 "future {not_trait} as it awaits another future which {not_trait}",
2508 not_trait = trait_explanation
2509 ),
2510 );
2511 } else {
2512 // Look at the last interior type to get a span for the `.await`.
2513 debug!(
2514 generator_interior_types = ?format_args!(
2515 "{:#?}", typeck_results.as_ref().map(|t| &t.generator_interior_types)
2516 ),
2517 );
2518 explain_yield(interior_span, yield_span, scope_span);
2519 }
2520
2521 if let Some(expr_id) = expr {
2522 let expr = hir.expect_expr(expr_id);
2523 debug!("target_ty evaluated from {:?}", expr);
2524
2525 let parent = hir.parent_id(expr_id);
2526 if let Some(hir::Node::Expr(e)) = hir.find(parent) {
2527 let parent_span = hir.span(parent);
2528 let parent_did = parent.owner.to_def_id();
2529 // ```rust
2530 // impl T {
2531 // fn foo(&self) -> i32 {}
2532 // }
2533 // T.foo();
2534 // ^^^^^^^ a temporary `&T` created inside this method call due to `&self`
2535 // ```
2536 //
2537 let is_region_borrow = if let Some(typeck_results) = typeck_results {
2538 typeck_results
2539 .expr_adjustments(expr)
2540 .iter()
2541 .any(|adj| adj.is_region_borrow())
2542 } else {
2543 false
2544 };
2545
2546 // ```rust
2547 // struct Foo(*const u8);
2548 // bar(Foo(std::ptr::null())).await;
2549 // ^^^^^^^^^^^^^^^^^^^^^ raw-ptr `*T` created inside this struct ctor.
2550 // ```
2551 debug!(parent_def_kind = ?self.tcx.def_kind(parent_did));
2552 let is_raw_borrow_inside_fn_like_call =
2553 match self.tcx.def_kind(parent_did) {
2554 DefKind::Fn | DefKind::Ctor(..) => target_ty.is_unsafe_ptr(),
2555 _ => false,
2556 };
2557 if let Some(typeck_results) = typeck_results {
2558 if (typeck_results.is_method_call(e) && is_region_borrow)
2559 || is_raw_borrow_inside_fn_like_call
2560 {
2561 err.span_help(
2562 parent_span,
2563 "consider moving this into a `let` \
2564 binding to create a shorter lived borrow",
2565 );
2566 }
2567 }
2568 }
2569 }
2570 }
2571 }
2572 GeneratorInteriorOrUpvar::Upvar(upvar_span) => {
2573 // `Some((ref_ty, is_mut))` if `target_ty` is `&T` or `&mut T` and fails to impl `Send`
2574 let non_send = match target_ty.kind() {
2575 ty::Ref(_, ref_ty, mutability) => match self.evaluate_obligation(&obligation) {
2576 Ok(eval) if !eval.may_apply() => Some((ref_ty, mutability.is_mut())),
2577 _ => None,
2578 },
2579 _ => None,
2580 };
2581
2582 let (span_label, span_note) = match non_send {
2583 // if `target_ty` is `&T` or `&mut T` and fails to impl `Send`,
2584 // include suggestions to make `T: Sync` so that `&T: Send`,
2585 // or to make `T: Send` so that `&mut T: Send`
2586 Some((ref_ty, is_mut)) => {
2587 let ref_ty_trait = if is_mut { "Send" } else { "Sync" };
2588 let ref_kind = if is_mut { "&mut" } else { "&" };
2589 (
2590 format!(
2591 "has type `{}` which {}, because `{}` is not `{}`",
2592 target_ty, trait_explanation, ref_ty, ref_ty_trait
2593 ),
2594 format!(
2595 "captured value {} because `{}` references cannot be sent unless their referent is `{}`",
2596 trait_explanation, ref_kind, ref_ty_trait
2597 ),
2598 )
2599 }
2600 None => (
2601 format!("has type `{}` which {}", target_ty, trait_explanation),
2602 format!("captured value {}", trait_explanation),
2603 ),
2604 };
2605
2606 let mut span = MultiSpan::from_span(upvar_span);
2607 span.push_span_label(upvar_span, span_label);
2608 err.span_note(span, span_note);
2609 }
2610 }
2611
2612 // Add a note for the item obligation that remains - normally a note pointing to the
2613 // bound that introduced the obligation (e.g. `T: Send`).
2614 debug!(?next_code);
2615 self.note_obligation_cause_code(
2616 obligation.cause.body_id,
2617 err,
2618 obligation.predicate,
2619 obligation.param_env,
2620 next_code.unwrap(),
2621 &mut Vec::new(),
2622 &mut Default::default(),
2623 );
2624 }
2625
note_obligation_cause_code<T>( &self, body_id: LocalDefId, err: &mut Diagnostic, predicate: T, param_env: ty::ParamEnv<'tcx>, cause_code: &ObligationCauseCode<'tcx>, obligated_types: &mut Vec<Ty<'tcx>>, seen_requirements: &mut FxHashSet<DefId>, ) where T: ToPredicate<'tcx>,2626 fn note_obligation_cause_code<T>(
2627 &self,
2628 body_id: LocalDefId,
2629 err: &mut Diagnostic,
2630 predicate: T,
2631 param_env: ty::ParamEnv<'tcx>,
2632 cause_code: &ObligationCauseCode<'tcx>,
2633 obligated_types: &mut Vec<Ty<'tcx>>,
2634 seen_requirements: &mut FxHashSet<DefId>,
2635 ) where
2636 T: ToPredicate<'tcx>,
2637 {
2638 let tcx = self.tcx;
2639 let predicate = predicate.to_predicate(tcx);
2640 match *cause_code {
2641 ObligationCauseCode::ExprAssignable
2642 | ObligationCauseCode::MatchExpressionArm { .. }
2643 | ObligationCauseCode::Pattern { .. }
2644 | ObligationCauseCode::IfExpression { .. }
2645 | ObligationCauseCode::IfExpressionWithNoElse
2646 | ObligationCauseCode::MainFunctionType
2647 | ObligationCauseCode::StartFunctionType
2648 | ObligationCauseCode::IntrinsicType
2649 | ObligationCauseCode::MethodReceiver
2650 | ObligationCauseCode::ReturnNoExpression
2651 | ObligationCauseCode::UnifyReceiver(..)
2652 | ObligationCauseCode::OpaqueType
2653 | ObligationCauseCode::MiscObligation
2654 | ObligationCauseCode::WellFormed(..)
2655 | ObligationCauseCode::MatchImpl(..)
2656 | ObligationCauseCode::ReturnType
2657 | ObligationCauseCode::ReturnValue(_)
2658 | ObligationCauseCode::BlockTailExpression(_)
2659 | ObligationCauseCode::AwaitableExpr(_)
2660 | ObligationCauseCode::ForLoopIterator
2661 | ObligationCauseCode::QuestionMark
2662 | ObligationCauseCode::CheckAssociatedTypeBounds { .. }
2663 | ObligationCauseCode::LetElse
2664 | ObligationCauseCode::BinOp { .. }
2665 | ObligationCauseCode::AscribeUserTypeProvePredicate(..)
2666 | ObligationCauseCode::DropImpl
2667 | ObligationCauseCode::ConstParam(_) => {}
2668 ObligationCauseCode::RustCall => {
2669 if let Some(pred) = predicate.to_opt_poly_trait_pred()
2670 && Some(pred.def_id()) == self.tcx.lang_items().sized_trait()
2671 {
2672 err.note("argument required to be sized due to `extern \"rust-call\"` ABI");
2673 }
2674 }
2675 ObligationCauseCode::SliceOrArrayElem => {
2676 err.note("slice and array elements must have `Sized` type");
2677 }
2678 ObligationCauseCode::TupleElem => {
2679 err.note("only the last element of a tuple may have a dynamically sized type");
2680 }
2681 ObligationCauseCode::ProjectionWf(data) => {
2682 err.note(format!("required so that the projection `{data}` is well-formed"));
2683 }
2684 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
2685 err.note(format!(
2686 "required so that reference `{ref_ty}` does not outlive its referent"
2687 ));
2688 }
2689 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
2690 err.note(format!(
2691 "required so that the lifetime bound of `{}` for `{}` is satisfied",
2692 region, object_ty,
2693 ));
2694 }
2695 ObligationCauseCode::ItemObligation(_)
2696 | ObligationCauseCode::ExprItemObligation(..) => {
2697 // We hold the `DefId` of the item introducing the obligation, but displaying it
2698 // doesn't add user usable information. It always point at an associated item.
2699 }
2700 ObligationCauseCode::BindingObligation(item_def_id, span)
2701 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..) => {
2702 let item_name = tcx.def_path_str(item_def_id);
2703 let short_item_name = with_forced_trimmed_paths!(tcx.def_path_str(item_def_id));
2704 let mut multispan = MultiSpan::from(span);
2705 let sm = tcx.sess.source_map();
2706 if let Some(ident) = tcx.opt_item_ident(item_def_id) {
2707 let same_line =
2708 match (sm.lookup_line(ident.span.hi()), sm.lookup_line(span.lo())) {
2709 (Ok(l), Ok(r)) => l.line == r.line,
2710 _ => true,
2711 };
2712 if ident.span.is_visible(sm) && !ident.span.overlaps(span) && !same_line {
2713 multispan.push_span_label(
2714 ident.span,
2715 format!(
2716 "required by a bound in this {}",
2717 tcx.def_kind(item_def_id).descr(item_def_id)
2718 ),
2719 );
2720 }
2721 }
2722 let descr = format!("required by a bound in `{item_name}`");
2723 if span.is_visible(sm) {
2724 let msg = format!("required by this bound in `{short_item_name}`");
2725 multispan.push_span_label(span, msg);
2726 err.span_note(multispan, descr);
2727 if let ty::PredicateKind::Clause(clause) = predicate.kind().skip_binder()
2728 && let ty::ClauseKind::Trait(trait_pred) = clause
2729 {
2730 let def_id = trait_pred.def_id();
2731 let visible_item = if let Some(local) = def_id.as_local() {
2732 // Check for local traits being reachable.
2733 let vis = &self.tcx.resolutions(()).effective_visibilities;
2734 // Account for non-`pub` traits in the root of the local crate.
2735 let is_locally_reachable = self.tcx.parent(def_id).is_crate_root();
2736 vis.is_reachable(local) || is_locally_reachable
2737 } else {
2738 // Check for foreign traits being reachable.
2739 self.tcx.visible_parent_map(()).get(&def_id).is_some()
2740 };
2741 if let DefKind::Trait = tcx.def_kind(item_def_id) && !visible_item {
2742 // FIXME(estebank): extend this to search for all the types that do
2743 // implement this trait and list them.
2744 err.note(format!(
2745 "`{short_item_name}` is a \"sealed trait\", because to implement \
2746 it you also need to implelement `{}`, which is not accessible; \
2747 this is usually done to force you to use one of the provided \
2748 types that already implement it",
2749 with_no_trimmed_paths!(tcx.def_path_str(def_id)),
2750 ));
2751 }
2752 }
2753 } else {
2754 err.span_note(tcx.def_span(item_def_id), descr);
2755 }
2756 }
2757 ObligationCauseCode::Coercion { source, target } => {
2758 let (source, source_file) =
2759 self.tcx.short_ty_string(self.resolve_vars_if_possible(source));
2760 let (target, target_file) =
2761 self.tcx.short_ty_string(self.resolve_vars_if_possible(target));
2762 err.note(with_forced_trimmed_paths!(format!(
2763 "required for the cast from `{source}` to `{target}`",
2764 )));
2765 if let Some(file) = source_file {
2766 err.note(format!(
2767 "the full name for the source type has been written to '{}'",
2768 file.display(),
2769 ));
2770 }
2771 if let Some(file) = target_file {
2772 err.note(format!(
2773 "the full name for the target type has been written to '{}'",
2774 file.display(),
2775 ));
2776 }
2777 }
2778 ObligationCauseCode::RepeatElementCopy { is_const_fn } => {
2779 err.note(
2780 "the `Copy` trait is required because this value will be copied for each element of the array",
2781 );
2782
2783 if is_const_fn {
2784 err.help(
2785 "consider creating a new `const` item and initializing it with the result \
2786 of the function call to be used in the repeat position, like \
2787 `const VAL: Type = const_fn();` and `let x = [VAL; 42];`",
2788 );
2789 }
2790
2791 if self.tcx.sess.is_nightly_build() && is_const_fn {
2792 err.help(
2793 "create an inline `const` block, see RFC #2920 \
2794 <https://github.com/rust-lang/rfcs/pull/2920> for more information",
2795 );
2796 }
2797 }
2798 ObligationCauseCode::VariableType(hir_id) => {
2799 let parent_node = self.tcx.hir().parent_id(hir_id);
2800 match self.tcx.hir().find(parent_node) {
2801 Some(Node::Local(hir::Local { ty: Some(ty), .. })) => {
2802 err.span_suggestion_verbose(
2803 ty.span.shrink_to_lo(),
2804 "consider borrowing here",
2805 "&",
2806 Applicability::MachineApplicable,
2807 );
2808 err.note("all local variables must have a statically known size");
2809 }
2810 Some(Node::Local(hir::Local {
2811 init: Some(hir::Expr { kind: hir::ExprKind::Index(_, _), span, .. }),
2812 ..
2813 })) => {
2814 // When encountering an assignment of an unsized trait, like
2815 // `let x = ""[..];`, provide a suggestion to borrow the initializer in
2816 // order to use have a slice instead.
2817 err.span_suggestion_verbose(
2818 span.shrink_to_lo(),
2819 "consider borrowing here",
2820 "&",
2821 Applicability::MachineApplicable,
2822 );
2823 err.note("all local variables must have a statically known size");
2824 }
2825 Some(Node::Param(param)) => {
2826 err.span_suggestion_verbose(
2827 param.ty_span.shrink_to_lo(),
2828 "function arguments must have a statically known size, borrowed types \
2829 always have a known size",
2830 "&",
2831 Applicability::MachineApplicable,
2832 );
2833 }
2834 _ => {
2835 err.note("all local variables must have a statically known size");
2836 }
2837 }
2838 if !self.tcx.features().unsized_locals {
2839 err.help("unsized locals are gated as an unstable feature");
2840 }
2841 }
2842 ObligationCauseCode::SizedArgumentType(ty_span) => {
2843 if let Some(span) = ty_span {
2844 if let ty::PredicateKind::Clause(clause) = predicate.kind().skip_binder()
2845 && let ty::ClauseKind::Trait(trait_pred) = clause
2846 && let ty::Dynamic(..) = trait_pred.self_ty().kind()
2847 {
2848 let span = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2849 && snippet.starts_with("dyn ")
2850 {
2851 let pos = snippet.len() - snippet[3..].trim_start().len();
2852 span.with_hi(span.lo() + BytePos(pos as u32))
2853 } else {
2854 span.shrink_to_lo()
2855 };
2856 err.span_suggestion_verbose(
2857 span,
2858 "you can use `impl Trait` as the argument type",
2859 "impl ".to_string(),
2860 Applicability::MaybeIncorrect,
2861 );
2862 }
2863 err.span_suggestion_verbose(
2864 span.shrink_to_lo(),
2865 "function arguments must have a statically known size, borrowed types \
2866 always have a known size",
2867 "&",
2868 Applicability::MachineApplicable,
2869 );
2870 } else {
2871 err.note("all function arguments must have a statically known size");
2872 }
2873 if tcx.sess.opts.unstable_features.is_nightly_build()
2874 && !self.tcx.features().unsized_fn_params
2875 {
2876 err.help("unsized fn params are gated as an unstable feature");
2877 }
2878 }
2879 ObligationCauseCode::SizedReturnType => {
2880 err.note("the return type of a function must have a statically known size");
2881 }
2882 ObligationCauseCode::SizedYieldType => {
2883 err.note("the yield type of a generator must have a statically known size");
2884 }
2885 ObligationCauseCode::AssignmentLhsSized => {
2886 err.note("the left-hand-side of an assignment must have a statically known size");
2887 }
2888 ObligationCauseCode::TupleInitializerSized => {
2889 err.note("tuples must have a statically known size to be initialized");
2890 }
2891 ObligationCauseCode::StructInitializerSized => {
2892 err.note("structs must have a statically known size to be initialized");
2893 }
2894 ObligationCauseCode::FieldSized { adt_kind: ref item, last, span } => {
2895 match *item {
2896 AdtKind::Struct => {
2897 if last {
2898 err.note(
2899 "the last field of a packed struct may only have a \
2900 dynamically sized type if it does not need drop to be run",
2901 );
2902 } else {
2903 err.note(
2904 "only the last field of a struct may have a dynamically sized type",
2905 );
2906 }
2907 }
2908 AdtKind::Union => {
2909 err.note("no field of a union may have a dynamically sized type");
2910 }
2911 AdtKind::Enum => {
2912 err.note("no field of an enum variant may have a dynamically sized type");
2913 }
2914 }
2915 err.help("change the field's type to have a statically known size");
2916 err.span_suggestion(
2917 span.shrink_to_lo(),
2918 "borrowed types always have a statically known size",
2919 "&",
2920 Applicability::MachineApplicable,
2921 );
2922 err.multipart_suggestion(
2923 "the `Box` type always has a statically known size and allocates its contents \
2924 in the heap",
2925 vec![
2926 (span.shrink_to_lo(), "Box<".to_string()),
2927 (span.shrink_to_hi(), ">".to_string()),
2928 ],
2929 Applicability::MachineApplicable,
2930 );
2931 }
2932 ObligationCauseCode::ConstSized => {
2933 err.note("constant expressions must have a statically known size");
2934 }
2935 ObligationCauseCode::InlineAsmSized => {
2936 err.note("all inline asm arguments must have a statically known size");
2937 }
2938 ObligationCauseCode::ConstPatternStructural => {
2939 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
2940 }
2941 ObligationCauseCode::SharedStatic => {
2942 err.note("shared static variables must have a type that implements `Sync`");
2943 }
2944 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
2945 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2946 let ty = parent_trait_ref.skip_binder().self_ty();
2947 if parent_trait_ref.references_error() {
2948 // NOTE(eddyb) this was `.cancel()`, but `err`
2949 // is borrowed, so we can't fully defuse it.
2950 err.downgrade_to_delayed_bug();
2951 return;
2952 }
2953
2954 // If the obligation for a tuple is set directly by a Generator or Closure,
2955 // then the tuple must be the one containing capture types.
2956 let is_upvar_tys_infer_tuple = if !matches!(ty.kind(), ty::Tuple(..)) {
2957 false
2958 } else {
2959 if let ObligationCauseCode::BuiltinDerivedObligation(data) = &*data.parent_code
2960 {
2961 let parent_trait_ref =
2962 self.resolve_vars_if_possible(data.parent_trait_pred);
2963 let nested_ty = parent_trait_ref.skip_binder().self_ty();
2964 matches!(nested_ty.kind(), ty::Generator(..))
2965 || matches!(nested_ty.kind(), ty::Closure(..))
2966 } else {
2967 false
2968 }
2969 };
2970
2971 // Don't print the tuple of capture types
2972 'print: {
2973 if !is_upvar_tys_infer_tuple {
2974 let msg = with_forced_trimmed_paths!(format!(
2975 "required because it appears within the type `{ty}`",
2976 ));
2977 match ty.kind() {
2978 ty::Adt(def, _) => match self.tcx.opt_item_ident(def.did()) {
2979 Some(ident) => err.span_note(ident.span, msg),
2980 None => err.note(msg),
2981 },
2982 ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) => {
2983 // If the previous type is async fn, this is the future generated by the body of an async function.
2984 // Avoid printing it twice (it was already printed in the `ty::Generator` arm below).
2985 let is_future = tcx.ty_is_opaque_future(ty);
2986 debug!(
2987 ?obligated_types,
2988 ?is_future,
2989 "note_obligation_cause_code: check for async fn"
2990 );
2991 if is_future
2992 && obligated_types.last().is_some_and(|ty| match ty.kind() {
2993 ty::Generator(last_def_id, ..) => {
2994 tcx.generator_is_async(*last_def_id)
2995 }
2996 _ => false,
2997 })
2998 {
2999 break 'print;
3000 }
3001 err.span_note(self.tcx.def_span(def_id), msg)
3002 }
3003 ty::GeneratorWitness(bound_tys) => {
3004 use std::fmt::Write;
3005
3006 // FIXME: this is kind of an unusual format for rustc, can we make it more clear?
3007 // Maybe we should just remove this note altogether?
3008 // FIXME: only print types which don't meet the trait requirement
3009 let mut msg =
3010 "required because it captures the following types: ".to_owned();
3011 for ty in bound_tys.skip_binder() {
3012 with_forced_trimmed_paths!(write!(msg, "`{}`, ", ty).unwrap());
3013 }
3014 err.note(msg.trim_end_matches(", ").to_string())
3015 }
3016 ty::GeneratorWitnessMIR(def_id, substs) => {
3017 use std::fmt::Write;
3018
3019 // FIXME: this is kind of an unusual format for rustc, can we make it more clear?
3020 // Maybe we should just remove this note altogether?
3021 // FIXME: only print types which don't meet the trait requirement
3022 let mut msg =
3023 "required because it captures the following types: ".to_owned();
3024 for bty in tcx.generator_hidden_types(*def_id) {
3025 let ty = bty.subst(tcx, substs);
3026 write!(msg, "`{}`, ", ty).unwrap();
3027 }
3028 err.note(msg.trim_end_matches(", ").to_string())
3029 }
3030 ty::Generator(def_id, _, _) => {
3031 let sp = self.tcx.def_span(def_id);
3032
3033 // Special-case this to say "async block" instead of `[static generator]`.
3034 let kind = tcx.generator_kind(def_id).unwrap().descr();
3035 err.span_note(
3036 sp,
3037 with_forced_trimmed_paths!(format!(
3038 "required because it's used within this {kind}",
3039 )),
3040 )
3041 }
3042 ty::Closure(def_id, _) => err.span_note(
3043 self.tcx.def_span(def_id),
3044 "required because it's used within this closure",
3045 ),
3046 ty::Str => err.note("`str` is considered to contain a `[u8]` slice for auto trait purposes"),
3047 _ => err.note(msg),
3048 };
3049 }
3050 }
3051
3052 obligated_types.push(ty);
3053
3054 let parent_predicate = parent_trait_ref;
3055 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
3056 // #74711: avoid a stack overflow
3057 ensure_sufficient_stack(|| {
3058 self.note_obligation_cause_code(
3059 body_id,
3060 err,
3061 parent_predicate,
3062 param_env,
3063 &data.parent_code,
3064 obligated_types,
3065 seen_requirements,
3066 )
3067 });
3068 } else {
3069 ensure_sufficient_stack(|| {
3070 self.note_obligation_cause_code(
3071 body_id,
3072 err,
3073 parent_predicate,
3074 param_env,
3075 cause_code.peel_derives(),
3076 obligated_types,
3077 seen_requirements,
3078 )
3079 });
3080 }
3081 }
3082 ObligationCauseCode::ImplDerivedObligation(ref data) => {
3083 let mut parent_trait_pred =
3084 self.resolve_vars_if_possible(data.derived.parent_trait_pred);
3085 parent_trait_pred.remap_constness_diag(param_env);
3086 let parent_def_id = parent_trait_pred.def_id();
3087 let (self_ty, file) =
3088 self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
3089 let msg = format!(
3090 "required for `{self_ty}` to implement `{}`",
3091 parent_trait_pred.print_modifiers_and_trait_path()
3092 );
3093 let mut is_auto_trait = false;
3094 match self.tcx.hir().get_if_local(data.impl_or_alias_def_id) {
3095 Some(Node::Item(hir::Item {
3096 kind: hir::ItemKind::Trait(is_auto, ..),
3097 ident,
3098 ..
3099 })) => {
3100 // FIXME: we should do something else so that it works even on crate foreign
3101 // auto traits.
3102 is_auto_trait = matches!(is_auto, hir::IsAuto::Yes);
3103 err.span_note(ident.span, msg);
3104 }
3105 Some(Node::Item(hir::Item {
3106 kind: hir::ItemKind::Impl(hir::Impl { of_trait, self_ty, .. }),
3107 ..
3108 })) => {
3109 let mut spans = Vec::with_capacity(2);
3110 if let Some(trait_ref) = of_trait {
3111 spans.push(trait_ref.path.span);
3112 }
3113 spans.push(self_ty.span);
3114 let mut spans: MultiSpan = spans.into();
3115 if matches!(
3116 self_ty.span.ctxt().outer_expn_data().kind,
3117 ExpnKind::Macro(MacroKind::Derive, _)
3118 ) || matches!(
3119 of_trait.as_ref().map(|t| t.path.span.ctxt().outer_expn_data().kind),
3120 Some(ExpnKind::Macro(MacroKind::Derive, _))
3121 ) {
3122 spans.push_span_label(
3123 data.span,
3124 "unsatisfied trait bound introduced in this `derive` macro",
3125 );
3126 } else if !data.span.is_dummy() && !data.span.overlaps(self_ty.span) {
3127 spans.push_span_label(
3128 data.span,
3129 "unsatisfied trait bound introduced here",
3130 );
3131 }
3132 err.span_note(spans, msg);
3133 }
3134 _ => {
3135 err.note(msg);
3136 }
3137 };
3138
3139 if let Some(file) = file {
3140 err.note(format!(
3141 "the full type name has been written to '{}'",
3142 file.display(),
3143 ));
3144 }
3145 let mut parent_predicate = parent_trait_pred;
3146 let mut data = &data.derived;
3147 let mut count = 0;
3148 seen_requirements.insert(parent_def_id);
3149 if is_auto_trait {
3150 // We don't want to point at the ADT saying "required because it appears within
3151 // the type `X`", like we would otherwise do in test `supertrait-auto-trait.rs`.
3152 while let ObligationCauseCode::BuiltinDerivedObligation(derived) =
3153 &*data.parent_code
3154 {
3155 let child_trait_ref =
3156 self.resolve_vars_if_possible(derived.parent_trait_pred);
3157 let child_def_id = child_trait_ref.def_id();
3158 if seen_requirements.insert(child_def_id) {
3159 break;
3160 }
3161 data = derived;
3162 parent_predicate = child_trait_ref.to_predicate(tcx);
3163 parent_trait_pred = child_trait_ref;
3164 }
3165 }
3166 while let ObligationCauseCode::ImplDerivedObligation(child) = &*data.parent_code {
3167 // Skip redundant recursive obligation notes. See `ui/issue-20413.rs`.
3168 let child_trait_pred =
3169 self.resolve_vars_if_possible(child.derived.parent_trait_pred);
3170 let child_def_id = child_trait_pred.def_id();
3171 if seen_requirements.insert(child_def_id) {
3172 break;
3173 }
3174 count += 1;
3175 data = &child.derived;
3176 parent_predicate = child_trait_pred.to_predicate(tcx);
3177 parent_trait_pred = child_trait_pred;
3178 }
3179 if count > 0 {
3180 err.note(format!(
3181 "{} redundant requirement{} hidden",
3182 count,
3183 pluralize!(count)
3184 ));
3185 let (self_ty, file) =
3186 self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
3187 err.note(format!(
3188 "required for `{self_ty}` to implement `{}`",
3189 parent_trait_pred.print_modifiers_and_trait_path()
3190 ));
3191 if let Some(file) = file {
3192 err.note(format!(
3193 "the full type name has been written to '{}'",
3194 file.display(),
3195 ));
3196 }
3197 }
3198 // #74711: avoid a stack overflow
3199 ensure_sufficient_stack(|| {
3200 self.note_obligation_cause_code(
3201 body_id,
3202 err,
3203 parent_predicate,
3204 param_env,
3205 &data.parent_code,
3206 obligated_types,
3207 seen_requirements,
3208 )
3209 });
3210 }
3211 ObligationCauseCode::DerivedObligation(ref data) => {
3212 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
3213 let parent_predicate = parent_trait_ref;
3214 // #74711: avoid a stack overflow
3215 ensure_sufficient_stack(|| {
3216 self.note_obligation_cause_code(
3217 body_id,
3218 err,
3219 parent_predicate,
3220 param_env,
3221 &data.parent_code,
3222 obligated_types,
3223 seen_requirements,
3224 )
3225 });
3226 }
3227 ObligationCauseCode::TypeAlias(ref nested, span, def_id) => {
3228 // #74711: avoid a stack overflow
3229 ensure_sufficient_stack(|| {
3230 self.note_obligation_cause_code(
3231 body_id,
3232 err,
3233 predicate,
3234 param_env,
3235 nested,
3236 obligated_types,
3237 seen_requirements,
3238 )
3239 });
3240 let mut multispan = MultiSpan::from(span);
3241 multispan.push_span_label(span, "required by this bound");
3242 err.span_note(
3243 multispan,
3244 format!(
3245 "required by a bound on the type alias `{}`",
3246 self.infcx.tcx.item_name(def_id)
3247 ),
3248 );
3249 }
3250 ObligationCauseCode::FunctionArgumentObligation {
3251 arg_hir_id,
3252 call_hir_id,
3253 ref parent_code,
3254 ..
3255 } => {
3256 self.note_function_argument_obligation(
3257 body_id,
3258 err,
3259 arg_hir_id,
3260 parent_code,
3261 param_env,
3262 predicate,
3263 call_hir_id,
3264 );
3265 ensure_sufficient_stack(|| {
3266 self.note_obligation_cause_code(
3267 body_id,
3268 err,
3269 predicate,
3270 param_env,
3271 &parent_code,
3272 obligated_types,
3273 seen_requirements,
3274 )
3275 });
3276 }
3277 ObligationCauseCode::CompareImplItemObligation { trait_item_def_id, kind, .. } => {
3278 let item_name = self.tcx.item_name(trait_item_def_id);
3279 let msg = format!(
3280 "the requirement `{predicate}` appears on the `impl`'s {kind} \
3281 `{item_name}` but not on the corresponding trait's {kind}",
3282 );
3283 let sp = self
3284 .tcx
3285 .opt_item_ident(trait_item_def_id)
3286 .map(|i| i.span)
3287 .unwrap_or_else(|| self.tcx.def_span(trait_item_def_id));
3288 let mut assoc_span: MultiSpan = sp.into();
3289 assoc_span.push_span_label(
3290 sp,
3291 format!("this trait's {kind} doesn't have the requirement `{predicate}`"),
3292 );
3293 if let Some(ident) = self
3294 .tcx
3295 .opt_associated_item(trait_item_def_id)
3296 .and_then(|i| self.tcx.opt_item_ident(i.container_id(self.tcx)))
3297 {
3298 assoc_span.push_span_label(ident.span, "in this trait");
3299 }
3300 err.span_note(assoc_span, msg);
3301 }
3302 ObligationCauseCode::TrivialBound => {
3303 err.help("see issue #48214");
3304 if tcx.sess.opts.unstable_features.is_nightly_build() {
3305 err.help("add `#![feature(trivial_bounds)]` to the crate attributes to enable");
3306 }
3307 }
3308 ObligationCauseCode::OpaqueReturnType(expr_info) => {
3309 if let Some((expr_ty, expr_span)) = expr_info {
3310 let expr_ty = with_forced_trimmed_paths!(self.ty_to_string(expr_ty));
3311 err.span_label(
3312 expr_span,
3313 with_forced_trimmed_paths!(format!(
3314 "return type was inferred to be `{expr_ty}` here",
3315 )),
3316 );
3317 }
3318 }
3319 }
3320 }
3321
3322 #[instrument(
3323 level = "debug", skip(self, err), fields(trait_pred.self_ty = ?trait_pred.self_ty())
3324 )]
suggest_await_before_try( &self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>, trait_pred: ty::PolyTraitPredicate<'tcx>, span: Span, )3325 fn suggest_await_before_try(
3326 &self,
3327 err: &mut Diagnostic,
3328 obligation: &PredicateObligation<'tcx>,
3329 trait_pred: ty::PolyTraitPredicate<'tcx>,
3330 span: Span,
3331 ) {
3332 if let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) {
3333 let body = self.tcx.hir().body(body_id);
3334 if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
3335 let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
3336
3337 let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
3338 let impls_future = self.type_implements_trait(
3339 future_trait,
3340 [self.tcx.erase_late_bound_regions(self_ty)],
3341 obligation.param_env,
3342 );
3343 if !impls_future.must_apply_modulo_regions() {
3344 return;
3345 }
3346
3347 let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
3348 // `<T as Future>::Output`
3349 let projection_ty = trait_pred.map_bound(|trait_pred| {
3350 Ty::new_projection(
3351 self.tcx,
3352 item_def_id,
3353 // Future::Output has no substs
3354 [trait_pred.self_ty()],
3355 )
3356 });
3357 let InferOk { value: projection_ty, .. } =
3358 self.at(&obligation.cause, obligation.param_env).normalize(projection_ty);
3359
3360 debug!(
3361 normalized_projection_type = ?self.resolve_vars_if_possible(projection_ty)
3362 );
3363 let try_obligation = self.mk_trait_obligation_with_new_self_ty(
3364 obligation.param_env,
3365 trait_pred.map_bound(|trait_pred| (trait_pred, projection_ty.skip_binder())),
3366 );
3367 debug!(try_trait_obligation = ?try_obligation);
3368 if self.predicate_may_hold(&try_obligation)
3369 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
3370 && snippet.ends_with('?')
3371 {
3372 err.span_suggestion_verbose(
3373 span.with_hi(span.hi() - BytePos(1)).shrink_to_hi(),
3374 "consider `await`ing on the `Future`",
3375 ".await",
3376 Applicability::MaybeIncorrect,
3377 );
3378 }
3379 }
3380 }
3381 }
3382
suggest_floating_point_literal( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_ref: &ty::PolyTraitRef<'tcx>, )3383 fn suggest_floating_point_literal(
3384 &self,
3385 obligation: &PredicateObligation<'tcx>,
3386 err: &mut Diagnostic,
3387 trait_ref: &ty::PolyTraitRef<'tcx>,
3388 ) {
3389 let rhs_span = match obligation.cause.code() {
3390 ObligationCauseCode::BinOp { rhs_span: Some(span), is_lit, .. } if *is_lit => span,
3391 _ => return,
3392 };
3393 if let ty::Float(_) = trait_ref.skip_binder().self_ty().kind()
3394 && let ty::Infer(InferTy::IntVar(_)) = trait_ref.skip_binder().substs.type_at(1).kind()
3395 {
3396 err.span_suggestion_verbose(
3397 rhs_span.shrink_to_hi(),
3398 "consider using a floating-point literal by writing it with `.0`",
3399 ".0",
3400 Applicability::MaybeIncorrect,
3401 );
3402 }
3403 }
3404
suggest_derive( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )3405 fn suggest_derive(
3406 &self,
3407 obligation: &PredicateObligation<'tcx>,
3408 err: &mut Diagnostic,
3409 trait_pred: ty::PolyTraitPredicate<'tcx>,
3410 ) {
3411 let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) else {
3412 return;
3413 };
3414 let (adt, substs) = match trait_pred.skip_binder().self_ty().kind() {
3415 ty::Adt(adt, substs) if adt.did().is_local() => (adt, substs),
3416 _ => return,
3417 };
3418 let can_derive = {
3419 let is_derivable_trait = match diagnostic_name {
3420 sym::Default => !adt.is_enum(),
3421 sym::PartialEq | sym::PartialOrd => {
3422 let rhs_ty = trait_pred.skip_binder().trait_ref.substs.type_at(1);
3423 trait_pred.skip_binder().self_ty() == rhs_ty
3424 }
3425 sym::Eq | sym::Ord | sym::Clone | sym::Copy | sym::Hash | sym::Debug => true,
3426 _ => false,
3427 };
3428 is_derivable_trait &&
3429 // Ensure all fields impl the trait.
3430 adt.all_fields().all(|field| {
3431 let field_ty = field.ty(self.tcx, substs);
3432 let trait_substs = match diagnostic_name {
3433 sym::PartialEq | sym::PartialOrd => {
3434 Some(field_ty)
3435 }
3436 _ => None,
3437 };
3438 let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
3439 trait_ref: ty::TraitRef::new(self.tcx,
3440 trait_pred.def_id(),
3441 [field_ty].into_iter().chain(trait_substs),
3442 ),
3443 ..*tr
3444 });
3445 let field_obl = Obligation::new(
3446 self.tcx,
3447 obligation.cause.clone(),
3448 obligation.param_env,
3449 trait_pred,
3450 );
3451 self.predicate_must_hold_modulo_regions(&field_obl)
3452 })
3453 };
3454 if can_derive {
3455 err.span_suggestion_verbose(
3456 self.tcx.def_span(adt.did()).shrink_to_lo(),
3457 format!(
3458 "consider annotating `{}` with `#[derive({})]`",
3459 trait_pred.skip_binder().self_ty(),
3460 diagnostic_name,
3461 ),
3462 format!("#[derive({})]\n", diagnostic_name),
3463 Applicability::MaybeIncorrect,
3464 );
3465 }
3466 }
3467
suggest_dereferencing_index( &self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>, )3468 fn suggest_dereferencing_index(
3469 &self,
3470 obligation: &PredicateObligation<'tcx>,
3471 err: &mut Diagnostic,
3472 trait_pred: ty::PolyTraitPredicate<'tcx>,
3473 ) {
3474 if let ObligationCauseCode::ImplDerivedObligation(_) = obligation.cause.code()
3475 && self.tcx.is_diagnostic_item(sym::SliceIndex, trait_pred.skip_binder().trait_ref.def_id)
3476 && let ty::Slice(_) = trait_pred.skip_binder().trait_ref.substs.type_at(1).kind()
3477 && let ty::Ref(_, inner_ty, _) = trait_pred.skip_binder().self_ty().kind()
3478 && let ty::Uint(ty::UintTy::Usize) = inner_ty.kind()
3479 {
3480 err.span_suggestion_verbose(
3481 obligation.cause.span.shrink_to_lo(),
3482 "dereference this index",
3483 '*',
3484 Applicability::MachineApplicable,
3485 );
3486 }
3487 }
note_function_argument_obligation( &self, body_id: LocalDefId, err: &mut Diagnostic, arg_hir_id: HirId, parent_code: &ObligationCauseCode<'tcx>, param_env: ty::ParamEnv<'tcx>, failed_pred: ty::Predicate<'tcx>, call_hir_id: HirId, )3488 fn note_function_argument_obligation(
3489 &self,
3490 body_id: LocalDefId,
3491 err: &mut Diagnostic,
3492 arg_hir_id: HirId,
3493 parent_code: &ObligationCauseCode<'tcx>,
3494 param_env: ty::ParamEnv<'tcx>,
3495 failed_pred: ty::Predicate<'tcx>,
3496 call_hir_id: HirId,
3497 ) {
3498 let tcx = self.tcx;
3499 let hir = tcx.hir();
3500 if let Some(Node::Expr(expr)) = hir.find(arg_hir_id)
3501 && let Some(typeck_results) = &self.typeck_results
3502 {
3503 if let hir::Expr { kind: hir::ExprKind::Block(..), .. } = expr {
3504 let expr = expr.peel_blocks();
3505 let ty = typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(Ty::new_misc_error(tcx,));
3506 let span = expr.span;
3507 if Some(span) != err.span.primary_span() {
3508 err.span_label(
3509 span,
3510 if ty.references_error() {
3511 String::new()
3512 } else {
3513 let ty = with_forced_trimmed_paths!(self.ty_to_string(ty));
3514 format!("this tail expression is of type `{ty}`")
3515 },
3516 );
3517 }
3518 }
3519
3520 // FIXME: visit the ty to see if there's any closure involved, and if there is,
3521 // check whether its evaluated return type is the same as the one corresponding
3522 // to an associated type (as seen from `trait_pred`) in the predicate. Like in
3523 // trait_pred `S: Sum<<Self as Iterator>::Item>` and predicate `i32: Sum<&()>`
3524 let mut type_diffs = vec![];
3525 if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = parent_code.deref()
3526 && let Some(node_substs) = typeck_results.node_substs_opt(call_hir_id)
3527 && let where_clauses = self.tcx.predicates_of(def_id).instantiate(self.tcx, node_substs)
3528 && let Some(where_pred) = where_clauses.predicates.get(*idx)
3529 {
3530 if let Some(where_pred) = where_pred.as_trait_clause()
3531 && let Some(failed_pred) = failed_pred.to_opt_poly_trait_pred()
3532 {
3533 let where_pred = self.instantiate_binder_with_placeholders(where_pred);
3534 let failed_pred = self.instantiate_binder_with_fresh_vars(
3535 expr.span,
3536 LateBoundRegionConversionTime::FnCall,
3537 failed_pred
3538 );
3539
3540 let zipped =
3541 iter::zip(where_pred.trait_ref.substs, failed_pred.trait_ref.substs);
3542 for (expected, actual) in zipped {
3543 self.probe(|_| {
3544 match self
3545 .at(&ObligationCause::misc(expr.span, body_id), param_env)
3546 .eq(DefineOpaqueTypes::No, expected, actual)
3547 {
3548 Ok(_) => (), // We ignore nested obligations here for now.
3549 Err(err) => type_diffs.push(err),
3550 }
3551 })
3552 };
3553 } else if let Some(where_pred) = where_pred.as_projection_clause()
3554 && let Some(failed_pred) = failed_pred.to_opt_poly_projection_pred()
3555 && let Some(found) = failed_pred.skip_binder().term.ty()
3556 {
3557 type_diffs = vec![
3558 Sorts(ty::error::ExpectedFound {
3559 expected: Ty::new_alias(self.tcx,ty::Projection, where_pred.skip_binder().projection_ty),
3560 found,
3561 }),
3562 ];
3563 }
3564 }
3565 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
3566 && let hir::Path { res: hir::def::Res::Local(hir_id), .. } = path
3567 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(*hir_id)
3568 && let parent_hir_id = self.tcx.hir().parent_id(binding.hir_id)
3569 && let Some(hir::Node::Local(local)) = self.tcx.hir().find(parent_hir_id)
3570 && let Some(binding_expr) = local.init
3571 {
3572 // If the expression we're calling on is a binding, we want to point at the
3573 // `let` when talking about the type. Otherwise we'll point at every part
3574 // of the method chain with the type.
3575 self.point_at_chain(binding_expr, &typeck_results, type_diffs, param_env, err);
3576 } else {
3577 self.point_at_chain(expr, &typeck_results, type_diffs, param_env, err);
3578 }
3579 }
3580 let call_node = hir.find(call_hir_id);
3581 if let Some(Node::Expr(hir::Expr {
3582 kind: hir::ExprKind::MethodCall(path, rcvr, ..), ..
3583 })) = call_node
3584 {
3585 if Some(rcvr.span) == err.span.primary_span() {
3586 err.replace_span_with(path.ident.span, true);
3587 }
3588 }
3589
3590 if let Some(Node::Expr(expr)) = hir.find(call_hir_id) {
3591 if let hir::ExprKind::Call(hir::Expr { span, .. }, _)
3592 | hir::ExprKind::MethodCall(
3593 hir::PathSegment { ident: Ident { span, .. }, .. },
3594 ..,
3595 ) = expr.kind
3596 {
3597 if Some(*span) != err.span.primary_span() {
3598 err.span_label(*span, "required by a bound introduced by this call");
3599 }
3600 }
3601
3602 if let hir::ExprKind::MethodCall(_, expr, ..) = expr.kind {
3603 self.suggest_option_method_if_applicable(failed_pred, param_env, err, expr);
3604 }
3605 }
3606 }
3607
suggest_option_method_if_applicable( &self, failed_pred: ty::Predicate<'tcx>, param_env: ty::ParamEnv<'tcx>, err: &mut Diagnostic, expr: &hir::Expr<'_>, )3608 fn suggest_option_method_if_applicable(
3609 &self,
3610 failed_pred: ty::Predicate<'tcx>,
3611 param_env: ty::ParamEnv<'tcx>,
3612 err: &mut Diagnostic,
3613 expr: &hir::Expr<'_>,
3614 ) {
3615 let tcx = self.tcx;
3616 let infcx = self.infcx;
3617 let Some(typeck_results) = self.typeck_results.as_ref() else { return };
3618
3619 // Make sure we're dealing with the `Option` type.
3620 let Some(option_ty_adt) = typeck_results.expr_ty_adjusted(expr).ty_adt_def() else { return };
3621 if !tcx.is_diagnostic_item(sym::Option, option_ty_adt.did()) {
3622 return;
3623 }
3624
3625 // Given the predicate `fn(&T): FnOnce<(U,)>`, extract `fn(&T)` and `(U,)`,
3626 // then suggest `Option::as_deref(_mut)` if `U` can deref to `T`
3627 if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(ty::TraitPredicate { trait_ref, .. }))
3628 = failed_pred.kind().skip_binder()
3629 && tcx.is_fn_trait(trait_ref.def_id)
3630 && let [self_ty, found_ty] = trait_ref.substs.as_slice()
3631 && let Some(fn_ty) = self_ty.as_type().filter(|ty| ty.is_fn())
3632 && let fn_sig @ ty::FnSig {
3633 abi: abi::Abi::Rust,
3634 c_variadic: false,
3635 unsafety: hir::Unsafety::Normal,
3636 ..
3637 } = fn_ty.fn_sig(tcx).skip_binder()
3638
3639 // Extract first param of fn sig with peeled refs, e.g. `fn(&T)` -> `T`
3640 && let Some(&ty::Ref(_, target_ty, needs_mut)) = fn_sig.inputs().first().map(|t| t.kind())
3641 && !target_ty.has_escaping_bound_vars()
3642
3643 // Extract first tuple element out of fn trait, e.g. `FnOnce<(U,)>` -> `U`
3644 && let Some(ty::Tuple(tys)) = found_ty.as_type().map(Ty::kind)
3645 && let &[found_ty] = tys.as_slice()
3646 && !found_ty.has_escaping_bound_vars()
3647
3648 // Extract `<U as Deref>::Target` assoc type and check that it is `T`
3649 && let Some(deref_target_did) = tcx.lang_items().deref_target()
3650 && let projection = Ty::new_projection(tcx,deref_target_did, tcx.mk_substs(&[ty::GenericArg::from(found_ty)]))
3651 && let InferOk { value: deref_target, obligations } = infcx.at(&ObligationCause::dummy(), param_env).normalize(projection)
3652 && obligations.iter().all(|obligation| infcx.predicate_must_hold_modulo_regions(obligation))
3653 && infcx.can_eq(param_env, deref_target, target_ty)
3654 {
3655 let help = if let hir::Mutability::Mut = needs_mut
3656 && let Some(deref_mut_did) = tcx.lang_items().deref_mut_trait()
3657 && infcx
3658 .type_implements_trait(deref_mut_did, iter::once(found_ty), param_env)
3659 .must_apply_modulo_regions()
3660 {
3661 Some(("call `Option::as_deref_mut()` first", ".as_deref_mut()"))
3662 } else if let hir::Mutability::Not = needs_mut {
3663 Some(("call `Option::as_deref()` first", ".as_deref()"))
3664 } else {
3665 None
3666 };
3667
3668 if let Some((msg, sugg)) = help {
3669 err.span_suggestion_with_style(
3670 expr.span.shrink_to_hi(),
3671 msg,
3672 sugg,
3673 Applicability::MaybeIncorrect,
3674 SuggestionStyle::ShowAlways
3675 );
3676 }
3677 }
3678 }
3679
point_at_chain( &self, expr: &hir::Expr<'_>, typeck_results: &TypeckResults<'tcx>, type_diffs: Vec<TypeError<'tcx>>, param_env: ty::ParamEnv<'tcx>, err: &mut Diagnostic, )3680 fn point_at_chain(
3681 &self,
3682 expr: &hir::Expr<'_>,
3683 typeck_results: &TypeckResults<'tcx>,
3684 type_diffs: Vec<TypeError<'tcx>>,
3685 param_env: ty::ParamEnv<'tcx>,
3686 err: &mut Diagnostic,
3687 ) {
3688 let mut primary_spans = vec![];
3689 let mut span_labels = vec![];
3690
3691 let tcx = self.tcx;
3692
3693 let mut print_root_expr = true;
3694 let mut assocs = vec![];
3695 let mut expr = expr;
3696 let mut prev_ty = self.resolve_vars_if_possible(
3697 typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(Ty::new_misc_error(tcx)),
3698 );
3699 while let hir::ExprKind::MethodCall(_path_segment, rcvr_expr, _args, span) = expr.kind {
3700 // Point at every method call in the chain with the resulting type.
3701 // vec![1, 2, 3].iter().map(mapper).sum<i32>()
3702 // ^^^^^^ ^^^^^^^^^^^
3703 expr = rcvr_expr;
3704 let assocs_in_this_method =
3705 self.probe_assoc_types_at_expr(&type_diffs, span, prev_ty, expr.hir_id, param_env);
3706 assocs.push(assocs_in_this_method);
3707 prev_ty = self.resolve_vars_if_possible(
3708 typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(Ty::new_misc_error(tcx)),
3709 );
3710
3711 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
3712 && let hir::Path { res: hir::def::Res::Local(hir_id), .. } = path
3713 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(*hir_id)
3714 && let Some(parent) = self.tcx.hir().find_parent(binding.hir_id)
3715 {
3716 // We've reached the root of the method call chain...
3717 if let hir::Node::Local(local) = parent
3718 && let Some(binding_expr) = local.init
3719 {
3720 // ...and it is a binding. Get the binding creation and continue the chain.
3721 expr = binding_expr;
3722 }
3723 if let hir::Node::Param(param) = parent {
3724 // ...and it is a an fn argument.
3725 let prev_ty = self.resolve_vars_if_possible(
3726 typeck_results.node_type_opt(param.hir_id).unwrap_or(Ty::new_misc_error(tcx,)),
3727 );
3728 let assocs_in_this_method = self.probe_assoc_types_at_expr(&type_diffs, param.ty_span, prev_ty, param.hir_id, param_env);
3729 if assocs_in_this_method.iter().any(|a| a.is_some()) {
3730 assocs.push(assocs_in_this_method);
3731 print_root_expr = false;
3732 }
3733 break;
3734 }
3735 }
3736 }
3737 // We want the type before deref coercions, otherwise we talk about `&[_]`
3738 // instead of `Vec<_>`.
3739 if let Some(ty) = typeck_results.expr_ty_opt(expr) && print_root_expr {
3740 let ty = with_forced_trimmed_paths!(self.ty_to_string(ty));
3741 // Point at the root expression
3742 // vec![1, 2, 3].iter().map(mapper).sum<i32>()
3743 // ^^^^^^^^^^^^^
3744 span_labels.push((expr.span, format!("this expression has type `{ty}`")));
3745 };
3746 // Only show this if it is not a "trivial" expression (not a method
3747 // chain) and there are associated types to talk about.
3748 let mut assocs = assocs.into_iter().peekable();
3749 while let Some(assocs_in_method) = assocs.next() {
3750 let Some(prev_assoc_in_method) = assocs.peek() else {
3751 for entry in assocs_in_method {
3752 let Some((span, (assoc, ty))) = entry else { continue; };
3753 if primary_spans.is_empty() || type_diffs.iter().any(|diff| {
3754 let Sorts(expected_found) = diff else { return false; };
3755 self.can_eq(param_env, expected_found.found, ty)
3756 }) {
3757 // FIXME: this doesn't quite work for `Iterator::collect`
3758 // because we have `Vec<i32>` and `()`, but we'd want `i32`
3759 // to point at the `.into_iter()` call, but as long as we
3760 // still point at the other method calls that might have
3761 // introduced the issue, this is fine for now.
3762 primary_spans.push(span);
3763 }
3764 span_labels.push((
3765 span,
3766 with_forced_trimmed_paths!(format!(
3767 "`{}` is `{ty}` here",
3768 self.tcx.def_path_str(assoc),
3769 )),
3770 ));
3771 }
3772 break;
3773 };
3774 for (entry, prev_entry) in
3775 assocs_in_method.into_iter().zip(prev_assoc_in_method.into_iter())
3776 {
3777 match (entry, prev_entry) {
3778 (Some((span, (assoc, ty))), Some((_, (_, prev_ty)))) => {
3779 let ty_str = with_forced_trimmed_paths!(self.ty_to_string(ty));
3780
3781 let assoc = with_forced_trimmed_paths!(self.tcx.def_path_str(assoc));
3782 if !self.can_eq(param_env, ty, *prev_ty) {
3783 if type_diffs.iter().any(|diff| {
3784 let Sorts(expected_found) = diff else { return false; };
3785 self.can_eq(param_env, expected_found.found, ty)
3786 }) {
3787 primary_spans.push(span);
3788 }
3789 span_labels
3790 .push((span, format!("`{assoc}` changed to `{ty_str}` here")));
3791 } else {
3792 span_labels.push((span, format!("`{assoc}` remains `{ty_str}` here")));
3793 }
3794 }
3795 (Some((span, (assoc, ty))), None) => {
3796 span_labels.push((
3797 span,
3798 with_forced_trimmed_paths!(format!(
3799 "`{}` is `{}` here",
3800 self.tcx.def_path_str(assoc),
3801 self.ty_to_string(ty),
3802 )),
3803 ));
3804 }
3805 (None, Some(_)) | (None, None) => {}
3806 }
3807 }
3808 }
3809 if !primary_spans.is_empty() {
3810 let mut multi_span: MultiSpan = primary_spans.into();
3811 for (span, label) in span_labels {
3812 multi_span.push_span_label(span, label);
3813 }
3814 err.span_note(
3815 multi_span,
3816 "the method call chain might not have had the expected associated types",
3817 );
3818 }
3819 }
3820
probe_assoc_types_at_expr( &self, type_diffs: &[TypeError<'tcx>], span: Span, prev_ty: Ty<'tcx>, body_id: hir::HirId, param_env: ty::ParamEnv<'tcx>, ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>>3821 fn probe_assoc_types_at_expr(
3822 &self,
3823 type_diffs: &[TypeError<'tcx>],
3824 span: Span,
3825 prev_ty: Ty<'tcx>,
3826 body_id: hir::HirId,
3827 param_env: ty::ParamEnv<'tcx>,
3828 ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>> {
3829 let ocx = ObligationCtxt::new(self.infcx);
3830 let mut assocs_in_this_method = Vec::with_capacity(type_diffs.len());
3831 for diff in type_diffs {
3832 let Sorts(expected_found) = diff else { continue; };
3833 let ty::Alias(ty::Projection, proj) = expected_found.expected.kind() else { continue; };
3834
3835 let origin = TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span };
3836 let trait_def_id = proj.trait_def_id(self.tcx);
3837 // Make `Self` be equivalent to the type of the call chain
3838 // expression we're looking at now, so that we can tell what
3839 // for example `Iterator::Item` is at this point in the chain.
3840 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
3841 match param.kind {
3842 ty::GenericParamDefKind::Type { .. } => {
3843 if param.index == 0 {
3844 return prev_ty.into();
3845 }
3846 }
3847 ty::GenericParamDefKind::Lifetime | ty::GenericParamDefKind::Const { .. } => {}
3848 }
3849 self.var_for_def(span, param)
3850 });
3851 // This will hold the resolved type of the associated type, if the
3852 // current expression implements the trait that associated type is
3853 // in. For example, this would be what `Iterator::Item` is here.
3854 let ty_var = self.infcx.next_ty_var(origin);
3855 // This corresponds to `<ExprTy as Iterator>::Item = _`.
3856 let projection = ty::Binder::dummy(ty::PredicateKind::Clause(
3857 ty::ClauseKind::Projection(ty::ProjectionPredicate {
3858 projection_ty: self.tcx.mk_alias_ty(proj.def_id, substs),
3859 term: ty_var.into(),
3860 }),
3861 ));
3862 let body_def_id = self.tcx.hir().enclosing_body_owner(body_id);
3863 // Add `<ExprTy as Iterator>::Item = _` obligation.
3864 ocx.register_obligation(Obligation::misc(
3865 self.tcx,
3866 span,
3867 body_def_id,
3868 param_env,
3869 projection,
3870 ));
3871 if ocx.select_where_possible().is_empty() {
3872 // `ty_var` now holds the type that `Item` is for `ExprTy`.
3873 let ty_var = self.resolve_vars_if_possible(ty_var);
3874 assocs_in_this_method.push(Some((span, (proj.def_id, ty_var))));
3875 } else {
3876 // `<ExprTy as Iterator>` didn't select, so likely we've
3877 // reached the end of the iterator chain, like the originating
3878 // `Vec<_>`.
3879 // Keep the space consistent for later zipping.
3880 assocs_in_this_method.push(None);
3881 }
3882 }
3883 assocs_in_this_method
3884 }
3885
3886 /// If the type that failed selection is an array or a reference to an array,
3887 /// but the trait is implemented for slices, suggest that the user converts
3888 /// the array into a slice.
maybe_suggest_convert_to_slice( &self, err: &mut Diagnostic, trait_ref: ty::PolyTraitRef<'tcx>, candidate_impls: &[ImplCandidate<'tcx>], span: Span, )3889 fn maybe_suggest_convert_to_slice(
3890 &self,
3891 err: &mut Diagnostic,
3892 trait_ref: ty::PolyTraitRef<'tcx>,
3893 candidate_impls: &[ImplCandidate<'tcx>],
3894 span: Span,
3895 ) {
3896 // Three cases where we can make a suggestion:
3897 // 1. `[T; _]` (array of T)
3898 // 2. `&[T; _]` (reference to array of T)
3899 // 3. `&mut [T; _]` (mutable reference to array of T)
3900 let (element_ty, mut mutability) = match *trait_ref.skip_binder().self_ty().kind() {
3901 ty::Array(element_ty, _) => (element_ty, None),
3902
3903 ty::Ref(_, pointee_ty, mutability) => match *pointee_ty.kind() {
3904 ty::Array(element_ty, _) => (element_ty, Some(mutability)),
3905 _ => return,
3906 },
3907
3908 _ => return,
3909 };
3910
3911 // Go through all the candidate impls to see if any of them is for
3912 // slices of `element_ty` with `mutability`.
3913 let mut is_slice = |candidate: Ty<'tcx>| match *candidate.kind() {
3914 ty::RawPtr(ty::TypeAndMut { ty: t, mutbl: m }) | ty::Ref(_, t, m) => {
3915 if matches!(*t.kind(), ty::Slice(e) if e == element_ty)
3916 && m == mutability.unwrap_or(m)
3917 {
3918 // Use the candidate's mutability going forward.
3919 mutability = Some(m);
3920 true
3921 } else {
3922 false
3923 }
3924 }
3925 _ => false,
3926 };
3927
3928 // Grab the first candidate that matches, if any, and make a suggestion.
3929 if let Some(slice_ty) = candidate_impls
3930 .iter()
3931 .map(|trait_ref| trait_ref.trait_ref.self_ty())
3932 .find(|t| is_slice(*t))
3933 {
3934 let msg = format!("convert the array to a `{}` slice instead", slice_ty);
3935
3936 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
3937 let mut suggestions = vec![];
3938 if snippet.starts_with('&') {
3939 } else if let Some(hir::Mutability::Mut) = mutability {
3940 suggestions.push((span.shrink_to_lo(), "&mut ".into()));
3941 } else {
3942 suggestions.push((span.shrink_to_lo(), "&".into()));
3943 }
3944 suggestions.push((span.shrink_to_hi(), "[..]".into()));
3945 err.multipart_suggestion_verbose(msg, suggestions, Applicability::MaybeIncorrect);
3946 } else {
3947 err.span_help(span, msg);
3948 }
3949 }
3950 }
3951 }
3952
3953 /// Add a hint to add a missing borrow or remove an unnecessary one.
hint_missing_borrow<'tcx>( infcx: &InferCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, span: Span, found: Ty<'tcx>, expected: Ty<'tcx>, found_node: Node<'_>, err: &mut Diagnostic, )3954 fn hint_missing_borrow<'tcx>(
3955 infcx: &InferCtxt<'tcx>,
3956 param_env: ty::ParamEnv<'tcx>,
3957 span: Span,
3958 found: Ty<'tcx>,
3959 expected: Ty<'tcx>,
3960 found_node: Node<'_>,
3961 err: &mut Diagnostic,
3962 ) {
3963 let found_args = match found.kind() {
3964 ty::FnPtr(f) => infcx.instantiate_binder_with_placeholders(*f).inputs().iter(),
3965 kind => {
3966 span_bug!(span, "found was converted to a FnPtr above but is now {:?}", kind)
3967 }
3968 };
3969 let expected_args = match expected.kind() {
3970 ty::FnPtr(f) => infcx.instantiate_binder_with_placeholders(*f).inputs().iter(),
3971 kind => {
3972 span_bug!(span, "expected was converted to a FnPtr above but is now {:?}", kind)
3973 }
3974 };
3975
3976 // This could be a variant constructor, for example.
3977 let Some(fn_decl) = found_node.fn_decl() else { return; };
3978
3979 let args = fn_decl.inputs.iter();
3980
3981 fn get_deref_type_and_refs(mut ty: Ty<'_>) -> (Ty<'_>, Vec<hir::Mutability>) {
3982 let mut refs = vec![];
3983
3984 while let ty::Ref(_, new_ty, mutbl) = ty.kind() {
3985 ty = *new_ty;
3986 refs.push(*mutbl);
3987 }
3988
3989 (ty, refs)
3990 }
3991
3992 let mut to_borrow = Vec::new();
3993 let mut remove_borrow = Vec::new();
3994
3995 for ((found_arg, expected_arg), arg) in found_args.zip(expected_args).zip(args) {
3996 let (found_ty, found_refs) = get_deref_type_and_refs(*found_arg);
3997 let (expected_ty, expected_refs) = get_deref_type_and_refs(*expected_arg);
3998
3999 if infcx.can_eq(param_env, found_ty, expected_ty) {
4000 // FIXME: This could handle more exotic cases like mutability mismatches too!
4001 if found_refs.len() < expected_refs.len()
4002 && found_refs[..] == expected_refs[expected_refs.len() - found_refs.len()..]
4003 {
4004 to_borrow.push((
4005 arg.span.shrink_to_lo(),
4006 expected_refs[..expected_refs.len() - found_refs.len()]
4007 .iter()
4008 .map(|mutbl| format!("&{}", mutbl.prefix_str()))
4009 .collect::<Vec<_>>()
4010 .join(""),
4011 ));
4012 } else if found_refs.len() > expected_refs.len() {
4013 let mut span = arg.span.shrink_to_lo();
4014 let mut left = found_refs.len() - expected_refs.len();
4015 let mut ty = arg;
4016 while let hir::TyKind::Ref(_, mut_ty) = &ty.kind && left > 0 {
4017 span = span.with_hi(mut_ty.ty.span.lo());
4018 ty = mut_ty.ty;
4019 left -= 1;
4020 }
4021 let sugg = if left == 0 {
4022 (span, String::new())
4023 } else {
4024 (arg.span, expected_arg.to_string())
4025 };
4026 remove_borrow.push(sugg);
4027 }
4028 }
4029 }
4030
4031 if !to_borrow.is_empty() {
4032 err.multipart_suggestion_verbose(
4033 "consider borrowing the argument",
4034 to_borrow,
4035 Applicability::MaybeIncorrect,
4036 );
4037 }
4038
4039 if !remove_borrow.is_empty() {
4040 err.multipart_suggestion_verbose(
4041 "do not borrow the argument",
4042 remove_borrow,
4043 Applicability::MaybeIncorrect,
4044 );
4045 }
4046 }
4047
4048 /// Collect all the returned expressions within the input expression.
4049 /// Used to point at the return spans when we want to suggest some change to them.
4050 #[derive(Default)]
4051 pub struct ReturnsVisitor<'v> {
4052 pub returns: Vec<&'v hir::Expr<'v>>,
4053 in_block_tail: bool,
4054 }
4055
4056 impl<'v> Visitor<'v> for ReturnsVisitor<'v> {
visit_expr(&mut self, ex: &'v hir::Expr<'v>)4057 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
4058 // Visit every expression to detect `return` paths, either through the function's tail
4059 // expression or `return` statements. We walk all nodes to find `return` statements, but
4060 // we only care about tail expressions when `in_block_tail` is `true`, which means that
4061 // they're in the return path of the function body.
4062 match ex.kind {
4063 hir::ExprKind::Ret(Some(ex)) => {
4064 self.returns.push(ex);
4065 }
4066 hir::ExprKind::Block(block, _) if self.in_block_tail => {
4067 self.in_block_tail = false;
4068 for stmt in block.stmts {
4069 hir::intravisit::walk_stmt(self, stmt);
4070 }
4071 self.in_block_tail = true;
4072 if let Some(expr) = block.expr {
4073 self.visit_expr(expr);
4074 }
4075 }
4076 hir::ExprKind::If(_, then, else_opt) if self.in_block_tail => {
4077 self.visit_expr(then);
4078 if let Some(el) = else_opt {
4079 self.visit_expr(el);
4080 }
4081 }
4082 hir::ExprKind::Match(_, arms, _) if self.in_block_tail => {
4083 for arm in arms {
4084 self.visit_expr(arm.body);
4085 }
4086 }
4087 // We need to walk to find `return`s in the entire body.
4088 _ if !self.in_block_tail => hir::intravisit::walk_expr(self, ex),
4089 _ => self.returns.push(ex),
4090 }
4091 }
4092
visit_body(&mut self, body: &'v hir::Body<'v>)4093 fn visit_body(&mut self, body: &'v hir::Body<'v>) {
4094 assert!(!self.in_block_tail);
4095 if body.generator_kind().is_none() {
4096 if let hir::ExprKind::Block(block, None) = body.value.kind {
4097 if block.expr.is_some() {
4098 self.in_block_tail = true;
4099 }
4100 }
4101 }
4102 hir::intravisit::walk_body(self, body);
4103 }
4104 }
4105
4106 /// Collect all the awaited expressions within the input expression.
4107 #[derive(Default)]
4108 struct AwaitsVisitor {
4109 awaits: Vec<hir::HirId>,
4110 }
4111
4112 impl<'v> Visitor<'v> for AwaitsVisitor {
visit_expr(&mut self, ex: &'v hir::Expr<'v>)4113 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
4114 if let hir::ExprKind::Yield(_, hir::YieldSource::Await { expr: Some(id) }) = ex.kind {
4115 self.awaits.push(id)
4116 }
4117 hir::intravisit::walk_expr(self, ex)
4118 }
4119 }
4120
4121 pub trait NextTypeParamName {
next_type_param_name(&self, name: Option<&str>) -> String4122 fn next_type_param_name(&self, name: Option<&str>) -> String;
4123 }
4124
4125 impl NextTypeParamName for &[hir::GenericParam<'_>] {
next_type_param_name(&self, name: Option<&str>) -> String4126 fn next_type_param_name(&self, name: Option<&str>) -> String {
4127 // This is the list of possible parameter names that we might suggest.
4128 let name = name.and_then(|n| n.chars().next()).map(|c| c.to_string().to_uppercase());
4129 let name = name.as_deref();
4130 let possible_names = [name.unwrap_or("T"), "T", "U", "V", "X", "Y", "Z", "A", "B", "C"];
4131 let used_names = self
4132 .iter()
4133 .filter_map(|p| match p.name {
4134 hir::ParamName::Plain(ident) => Some(ident.name),
4135 _ => None,
4136 })
4137 .collect::<Vec<_>>();
4138
4139 possible_names
4140 .iter()
4141 .find(|n| !used_names.contains(&Symbol::intern(n)))
4142 .unwrap_or(&"ParamName")
4143 .to_string()
4144 }
4145 }
4146
4147 /// Collect the spans that we see the generic param `param_did`
4148 struct ReplaceImplTraitVisitor<'a> {
4149 ty_spans: &'a mut Vec<Span>,
4150 param_did: DefId,
4151 }
4152
4153 impl<'a, 'hir> hir::intravisit::Visitor<'hir> for ReplaceImplTraitVisitor<'a> {
visit_ty(&mut self, t: &'hir hir::Ty<'hir>)4154 fn visit_ty(&mut self, t: &'hir hir::Ty<'hir>) {
4155 if let hir::TyKind::Path(hir::QPath::Resolved(
4156 None,
4157 hir::Path { res: hir::def::Res::Def(_, segment_did), .. },
4158 )) = t.kind
4159 {
4160 if self.param_did == *segment_did {
4161 // `fn foo(t: impl Trait)`
4162 // ^^^^^^^^^^ get this to suggest `T` instead
4163
4164 // There might be more than one `impl Trait`.
4165 self.ty_spans.push(t.span);
4166 return;
4167 }
4168 }
4169
4170 hir::intravisit::walk_ty(self, t);
4171 }
4172 }
4173
4174 // Replace `param` with `replace_ty`
4175 struct ReplaceImplTraitFolder<'tcx> {
4176 tcx: TyCtxt<'tcx>,
4177 param: &'tcx ty::GenericParamDef,
4178 replace_ty: Ty<'tcx>,
4179 }
4180
4181 impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReplaceImplTraitFolder<'tcx> {
fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx>4182 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
4183 if let ty::Param(ty::ParamTy { index, .. }) = t.kind() {
4184 if self.param.index == *index {
4185 return self.replace_ty;
4186 }
4187 }
4188 t.super_fold_with(self)
4189 }
4190
interner(&self) -> TyCtxt<'tcx>4191 fn interner(&self) -> TyCtxt<'tcx> {
4192 self.tcx
4193 }
4194 }
4195