1 use rustc_data_structures::fx::FxHashSet;
2 use rustc_hir as hir;
3 use rustc_hir::lang_items::LangItem;
4 use rustc_middle::ty::{self, Region, RegionVid, TypeFoldable};
5 use rustc_trait_selection::traits::auto_trait::{self, AutoTraitResult};
6 use thin_vec::ThinVec;
7
8 use std::fmt::Debug;
9
10 use super::*;
11
12 #[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)]
13 enum RegionTarget<'tcx> {
14 Region(Region<'tcx>),
15 RegionVid(RegionVid),
16 }
17
18 #[derive(Default, Debug, Clone)]
19 struct RegionDeps<'tcx> {
20 larger: FxHashSet<RegionTarget<'tcx>>,
21 smaller: FxHashSet<RegionTarget<'tcx>>,
22 }
23
24 pub(crate) struct AutoTraitFinder<'a, 'tcx> {
25 pub(crate) cx: &'a mut core::DocContext<'tcx>,
26 }
27
28 impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx>
29 where
30 'tcx: 'a, // should be an implied bound; rustc bug #98852.
31 {
new(cx: &'a mut core::DocContext<'tcx>) -> Self32 pub(crate) fn new(cx: &'a mut core::DocContext<'tcx>) -> Self {
33 AutoTraitFinder { cx }
34 }
35
generate_for_trait( &mut self, ty: Ty<'tcx>, trait_def_id: DefId, param_env: ty::ParamEnv<'tcx>, item_def_id: DefId, f: &auto_trait::AutoTraitFinder<'tcx>, discard_positive_impl: bool, ) -> Option<Item>36 fn generate_for_trait(
37 &mut self,
38 ty: Ty<'tcx>,
39 trait_def_id: DefId,
40 param_env: ty::ParamEnv<'tcx>,
41 item_def_id: DefId,
42 f: &auto_trait::AutoTraitFinder<'tcx>,
43 // If this is set, show only negative trait implementations, not positive ones.
44 discard_positive_impl: bool,
45 ) -> Option<Item> {
46 let tcx = self.cx.tcx;
47 let trait_ref = ty::Binder::dummy(ty::TraitRef::new(tcx, trait_def_id, [ty]));
48 if !self.cx.generated_synthetics.insert((ty, trait_def_id)) {
49 debug!("get_auto_trait_impl_for({:?}): already generated, aborting", trait_ref);
50 return None;
51 }
52
53 let result = f.find_auto_trait_generics(ty, param_env, trait_def_id, |info| {
54 let region_data = info.region_data;
55
56 let names_map = tcx
57 .generics_of(item_def_id)
58 .params
59 .iter()
60 .filter_map(|param| match param.kind {
61 ty::GenericParamDefKind::Lifetime => Some(param.name),
62 _ => None,
63 })
64 .map(|name| (name, Lifetime(name)))
65 .collect();
66 let lifetime_predicates = Self::handle_lifetimes(®ion_data, &names_map);
67 let new_generics = self.param_env_to_generics(
68 item_def_id,
69 info.full_user_env,
70 lifetime_predicates,
71 info.vid_to_region,
72 );
73
74 debug!(
75 "find_auto_trait_generics(item_def_id={:?}, trait_def_id={:?}): \
76 finished with {:?}",
77 item_def_id, trait_def_id, new_generics
78 );
79
80 new_generics
81 });
82
83 let polarity;
84 let new_generics = match result {
85 AutoTraitResult::PositiveImpl(new_generics) => {
86 polarity = ty::ImplPolarity::Positive;
87 if discard_positive_impl {
88 return None;
89 }
90 new_generics
91 }
92 AutoTraitResult::NegativeImpl => {
93 polarity = ty::ImplPolarity::Negative;
94
95 // For negative impls, we use the generic params, but *not* the predicates,
96 // from the original type. Otherwise, the displayed impl appears to be a
97 // conditional negative impl, when it's really unconditional.
98 //
99 // For example, consider the struct Foo<T: Copy>(*mut T). Using
100 // the original predicates in our impl would cause us to generate
101 // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
102 // implements Send where T is not copy.
103 //
104 // Instead, we generate `impl !Send for Foo<T>`, which better
105 // expresses the fact that `Foo<T>` never implements `Send`,
106 // regardless of the choice of `T`.
107 let raw_generics = clean_ty_generics(
108 self.cx,
109 tcx.generics_of(item_def_id),
110 ty::GenericPredicates::default(),
111 );
112 let params = raw_generics.params;
113
114 Generics { params, where_predicates: ThinVec::new() }
115 }
116 AutoTraitResult::ExplicitImpl => return None,
117 };
118
119 Some(Item {
120 name: None,
121 attrs: Default::default(),
122 item_id: ItemId::Auto { trait_: trait_def_id, for_: item_def_id },
123 kind: Box::new(ImplItem(Box::new(Impl {
124 unsafety: hir::Unsafety::Normal,
125 generics: new_generics,
126 trait_: Some(clean_trait_ref_with_bindings(self.cx, trait_ref, ThinVec::new())),
127 for_: clean_middle_ty(ty::Binder::dummy(ty), self.cx, None, None),
128 items: Vec::new(),
129 polarity,
130 kind: ImplKind::Auto,
131 }))),
132 cfg: None,
133 inline_stmt_id: None,
134 })
135 }
136
get_auto_trait_impls(&mut self, item_def_id: DefId) -> Vec<Item>137 pub(crate) fn get_auto_trait_impls(&mut self, item_def_id: DefId) -> Vec<Item> {
138 let tcx = self.cx.tcx;
139 let param_env = tcx.param_env(item_def_id);
140 let ty = tcx.type_of(item_def_id).subst_identity();
141 let f = auto_trait::AutoTraitFinder::new(tcx);
142
143 debug!("get_auto_trait_impls({:?})", ty);
144 let auto_traits: Vec<_> = self.cx.auto_traits.to_vec();
145 let mut auto_traits: Vec<Item> = auto_traits
146 .into_iter()
147 .filter_map(|trait_def_id| {
148 self.generate_for_trait(ty, trait_def_id, param_env, item_def_id, &f, false)
149 })
150 .collect();
151 // We are only interested in case the type *doesn't* implement the Sized trait.
152 if !ty.is_sized(tcx, param_env) {
153 // In case `#![no_core]` is used, `sized_trait` returns nothing.
154 if let Some(item) = tcx.lang_items().sized_trait().and_then(|sized_trait_did| {
155 self.generate_for_trait(ty, sized_trait_did, param_env, item_def_id, &f, true)
156 }) {
157 auto_traits.push(item);
158 }
159 }
160 auto_traits
161 }
162
get_lifetime(region: Region<'_>, names_map: &FxHashMap<Symbol, Lifetime>) -> Lifetime163 fn get_lifetime(region: Region<'_>, names_map: &FxHashMap<Symbol, Lifetime>) -> Lifetime {
164 region_name(region)
165 .map(|name| {
166 names_map.get(&name).unwrap_or_else(|| {
167 panic!("Missing lifetime with name {:?} for {:?}", name.as_str(), region)
168 })
169 })
170 .unwrap_or(&Lifetime::statik())
171 .clone()
172 }
173
174 /// This method calculates two things: Lifetime constraints of the form `'a: 'b`,
175 /// and region constraints of the form `RegionVid: 'a`
176 ///
177 /// This is essentially a simplified version of lexical_region_resolve. However,
178 /// handle_lifetimes determines what *needs be* true in order for an impl to hold.
179 /// lexical_region_resolve, along with much of the rest of the compiler, is concerned
180 /// with determining if a given set up constraints/predicates *are* met, given some
181 /// starting conditions (e.g., user-provided code). For this reason, it's easier
182 /// to perform the calculations we need on our own, rather than trying to make
183 /// existing inference/solver code do what we want.
handle_lifetimes<'cx>( regions: &RegionConstraintData<'cx>, names_map: &FxHashMap<Symbol, Lifetime>, ) -> ThinVec<WherePredicate>184 fn handle_lifetimes<'cx>(
185 regions: &RegionConstraintData<'cx>,
186 names_map: &FxHashMap<Symbol, Lifetime>,
187 ) -> ThinVec<WherePredicate> {
188 // Our goal is to 'flatten' the list of constraints by eliminating
189 // all intermediate RegionVids. At the end, all constraints should
190 // be between Regions (aka region variables). This gives us the information
191 // we need to create the Generics.
192 let mut finished: FxHashMap<_, Vec<_>> = Default::default();
193
194 let mut vid_map: FxHashMap<RegionTarget<'_>, RegionDeps<'_>> = Default::default();
195
196 // Flattening is done in two parts. First, we insert all of the constraints
197 // into a map. Each RegionTarget (either a RegionVid or a Region) maps
198 // to its smaller and larger regions. Note that 'larger' regions correspond
199 // to sub-regions in Rust code (e.g., in 'a: 'b, 'a is the larger region).
200 for constraint in regions.constraints.keys() {
201 match *constraint {
202 Constraint::VarSubVar(r1, r2) => {
203 {
204 let deps1 = vid_map.entry(RegionTarget::RegionVid(r1)).or_default();
205 deps1.larger.insert(RegionTarget::RegionVid(r2));
206 }
207
208 let deps2 = vid_map.entry(RegionTarget::RegionVid(r2)).or_default();
209 deps2.smaller.insert(RegionTarget::RegionVid(r1));
210 }
211 Constraint::RegSubVar(region, vid) => {
212 let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
213 deps.smaller.insert(RegionTarget::Region(region));
214 }
215 Constraint::VarSubReg(vid, region) => {
216 let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
217 deps.larger.insert(RegionTarget::Region(region));
218 }
219 Constraint::RegSubReg(r1, r2) => {
220 // The constraint is already in the form that we want, so we're done with it
221 // Desired order is 'larger, smaller', so flip then
222 if region_name(r1) != region_name(r2) {
223 finished
224 .entry(region_name(r2).expect("no region_name found"))
225 .or_default()
226 .push(r1);
227 }
228 }
229 }
230 }
231
232 // Here, we 'flatten' the map one element at a time.
233 // All of the element's sub and super regions are connected
234 // to each other. For example, if we have a graph that looks like this:
235 //
236 // (A, B) - C - (D, E)
237 // Where (A, B) are subregions, and (D,E) are super-regions
238 //
239 // then after deleting 'C', the graph will look like this:
240 // ... - A - (D, E ...)
241 // ... - B - (D, E, ...)
242 // (A, B, ...) - D - ...
243 // (A, B, ...) - E - ...
244 //
245 // where '...' signifies the existing sub and super regions of an entry
246 // When two adjacent ty::Regions are encountered, we've computed a final
247 // constraint, and add it to our list. Since we make sure to never re-add
248 // deleted items, this process will always finish.
249 while !vid_map.is_empty() {
250 let target = *vid_map.keys().next().expect("Keys somehow empty");
251 let deps = vid_map.remove(&target).expect("Entry somehow missing");
252
253 for smaller in deps.smaller.iter() {
254 for larger in deps.larger.iter() {
255 match (smaller, larger) {
256 (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
257 if region_name(r1) != region_name(r2) {
258 finished
259 .entry(region_name(r2).expect("no region name found"))
260 .or_default()
261 .push(r1) // Larger, smaller
262 }
263 }
264 (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
265 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
266 let smaller_deps = v.into_mut();
267 smaller_deps.larger.insert(*larger);
268 smaller_deps.larger.remove(&target);
269 }
270 }
271 (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
272 if let Entry::Occupied(v) = vid_map.entry(*larger) {
273 let deps = v.into_mut();
274 deps.smaller.insert(*smaller);
275 deps.smaller.remove(&target);
276 }
277 }
278 (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
279 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
280 let smaller_deps = v.into_mut();
281 smaller_deps.larger.insert(*larger);
282 smaller_deps.larger.remove(&target);
283 }
284
285 if let Entry::Occupied(v) = vid_map.entry(*larger) {
286 let larger_deps = v.into_mut();
287 larger_deps.smaller.insert(*smaller);
288 larger_deps.smaller.remove(&target);
289 }
290 }
291 }
292 }
293 }
294 }
295
296 let lifetime_predicates = names_map
297 .iter()
298 .flat_map(|(name, lifetime)| {
299 let empty = Vec::new();
300 let bounds: FxHashSet<GenericBound> = finished
301 .get(name)
302 .unwrap_or(&empty)
303 .iter()
304 .map(|region| GenericBound::Outlives(Self::get_lifetime(*region, names_map)))
305 .collect();
306
307 if bounds.is_empty() {
308 return None;
309 }
310 Some(WherePredicate::RegionPredicate {
311 lifetime: lifetime.clone(),
312 bounds: bounds.into_iter().collect(),
313 })
314 })
315 .collect();
316
317 lifetime_predicates
318 }
319
extract_for_generics(&self, pred: ty::Clause<'tcx>) -> FxHashSet<GenericParamDef>320 fn extract_for_generics(&self, pred: ty::Clause<'tcx>) -> FxHashSet<GenericParamDef> {
321 let bound_predicate = pred.kind();
322 let tcx = self.cx.tcx;
323 let regions = match bound_predicate.skip_binder() {
324 ty::ClauseKind::Trait(poly_trait_pred) => {
325 tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_trait_pred))
326 }
327 ty::ClauseKind::Projection(poly_proj_pred) => {
328 tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_proj_pred))
329 }
330 _ => return FxHashSet::default(),
331 };
332
333 regions
334 .into_iter()
335 .filter_map(|br| {
336 match br {
337 // We only care about named late bound regions, as we need to add them
338 // to the 'for<>' section
339 ty::BrNamed(_, name) => Some(GenericParamDef::lifetime(name)),
340 _ => None,
341 }
342 })
343 .collect()
344 }
345
make_final_bounds( &self, ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>, ty_to_fn: FxHashMap<Type, (PolyTrait, Option<Type>)>, lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>, ) -> Vec<WherePredicate>346 fn make_final_bounds(
347 &self,
348 ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
349 ty_to_fn: FxHashMap<Type, (PolyTrait, Option<Type>)>,
350 lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
351 ) -> Vec<WherePredicate> {
352 ty_to_bounds
353 .into_iter()
354 .flat_map(|(ty, mut bounds)| {
355 if let Some((ref poly_trait, ref output)) = ty_to_fn.get(&ty) {
356 let mut new_path = poly_trait.trait_.clone();
357 let last_segment = new_path.segments.pop().expect("segments were empty");
358
359 let (old_input, old_output) = match last_segment.args {
360 GenericArgs::AngleBracketed { args, .. } => {
361 let types = args
362 .iter()
363 .filter_map(|arg| match arg {
364 GenericArg::Type(ty) => Some(ty.clone()),
365 _ => None,
366 })
367 .collect();
368 (types, None)
369 }
370 GenericArgs::Parenthesized { inputs, output } => (inputs, output),
371 };
372
373 let output = output.as_ref().cloned().map(Box::new);
374 if old_output.is_some() && old_output != output {
375 panic!("Output mismatch for {:?} {:?} {:?}", ty, old_output, output);
376 }
377
378 let new_params = GenericArgs::Parenthesized { inputs: old_input, output };
379
380 new_path
381 .segments
382 .push(PathSegment { name: last_segment.name, args: new_params });
383
384 bounds.insert(GenericBound::TraitBound(
385 PolyTrait {
386 trait_: new_path,
387 generic_params: poly_trait.generic_params.clone(),
388 },
389 hir::TraitBoundModifier::None,
390 ));
391 }
392 if bounds.is_empty() {
393 return None;
394 }
395
396 let mut bounds_vec = bounds.into_iter().collect();
397 self.sort_where_bounds(&mut bounds_vec);
398
399 Some(WherePredicate::BoundPredicate {
400 ty,
401 bounds: bounds_vec,
402 bound_params: Vec::new(),
403 })
404 })
405 .chain(lifetime_to_bounds.into_iter().filter(|(_, bounds)| !bounds.is_empty()).map(
406 |(lifetime, bounds)| {
407 let mut bounds_vec = bounds.into_iter().collect();
408 self.sort_where_bounds(&mut bounds_vec);
409 WherePredicate::RegionPredicate { lifetime, bounds: bounds_vec }
410 },
411 ))
412 .collect()
413 }
414
415 /// Converts the calculated `ParamEnv` and lifetime information to a [`clean::Generics`](Generics), suitable for
416 /// display on the docs page. Cleaning the `Predicates` produces sub-optimal [`WherePredicate`]s,
417 /// so we fix them up:
418 ///
419 /// * Multiple bounds for the same type are coalesced into one: e.g., `T: Copy`, `T: Debug`
420 /// becomes `T: Copy + Debug`
421 /// * `Fn` bounds are handled specially - instead of leaving it as `T: Fn(), <T as Fn::Output> =
422 /// K`, we use the dedicated syntax `T: Fn() -> K`
423 /// * We explicitly add a `?Sized` bound if we didn't find any `Sized` predicates for a type
param_env_to_generics( &mut self, item_def_id: DefId, param_env: ty::ParamEnv<'tcx>, mut existing_predicates: ThinVec<WherePredicate>, vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'tcx>>, ) -> Generics424 fn param_env_to_generics(
425 &mut self,
426 item_def_id: DefId,
427 param_env: ty::ParamEnv<'tcx>,
428 mut existing_predicates: ThinVec<WherePredicate>,
429 vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
430 ) -> Generics {
431 debug!(
432 "param_env_to_generics(item_def_id={:?}, param_env={:?}, \
433 existing_predicates={:?})",
434 item_def_id, param_env, existing_predicates
435 );
436
437 let tcx = self.cx.tcx;
438
439 // The `Sized` trait must be handled specially, since we only display it when
440 // it is *not* required (i.e., '?Sized')
441 let sized_trait = tcx.require_lang_item(LangItem::Sized, None);
442
443 let mut replacer = RegionReplacer { vid_to_region: &vid_to_region, tcx };
444
445 let orig_bounds: FxHashSet<_> = tcx.param_env(item_def_id).caller_bounds().iter().collect();
446 let clean_where_predicates = param_env
447 .caller_bounds()
448 .iter()
449 .filter(|p| {
450 !orig_bounds.contains(p)
451 || match p.kind().skip_binder() {
452 ty::ClauseKind::Trait(pred) => pred.def_id() == sized_trait,
453 _ => false,
454 }
455 })
456 .map(|p| p.fold_with(&mut replacer));
457
458 let raw_generics = clean_ty_generics(
459 self.cx,
460 tcx.generics_of(item_def_id),
461 tcx.explicit_predicates_of(item_def_id),
462 );
463 let mut generic_params = raw_generics.params;
464
465 debug!("param_env_to_generics({:?}): generic_params={:?}", item_def_id, generic_params);
466
467 let mut has_sized = FxHashSet::default();
468 let mut ty_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
469 let mut lifetime_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
470 let mut ty_to_traits: FxHashMap<Type, FxHashSet<Path>> = Default::default();
471
472 let mut ty_to_fn: FxHashMap<Type, (PolyTrait, Option<Type>)> = Default::default();
473
474 // FIXME: This code shares much of the logic found in `clean_ty_generics` and
475 // `simplify::where_clause`. Consider deduplicating it to avoid diverging
476 // implementations.
477 // Further, the code below does not merge (partially re-sugared) bounds like
478 // `Tr<A = T>` & `Tr<B = U>` and it does not render higher-ranked parameters
479 // originating from equality predicates.
480 for p in clean_where_predicates {
481 let (orig_p, p) = (p, clean_predicate(p, self.cx));
482 if p.is_none() {
483 continue;
484 }
485 let p = p.unwrap();
486 match p {
487 WherePredicate::BoundPredicate { ty, mut bounds, .. } => {
488 // Writing a projection trait bound of the form
489 // <T as Trait>::Name : ?Sized
490 // is illegal, because ?Sized bounds can only
491 // be written in the (here, nonexistent) definition
492 // of the type.
493 // Therefore, we make sure that we never add a ?Sized
494 // bound for projections
495 if let Type::QPath { .. } = ty {
496 has_sized.insert(ty.clone());
497 }
498
499 if bounds.is_empty() {
500 continue;
501 }
502
503 let mut for_generics = self.extract_for_generics(orig_p);
504
505 assert!(bounds.len() == 1);
506 let mut b = bounds.pop().expect("bounds were empty");
507
508 if b.is_sized_bound(self.cx) {
509 has_sized.insert(ty.clone());
510 } else if !b
511 .get_trait_path()
512 .and_then(|trait_| {
513 ty_to_traits
514 .get(&ty)
515 .map(|bounds| bounds.contains(&strip_path_generics(trait_)))
516 })
517 .unwrap_or(false)
518 {
519 // If we've already added a projection bound for the same type, don't add
520 // this, as it would be a duplicate
521
522 // Handle any 'Fn/FnOnce/FnMut' bounds specially,
523 // as we want to combine them with any 'Output' qpaths
524 // later
525
526 let is_fn = match b {
527 GenericBound::TraitBound(ref mut p, _) => {
528 // Insert regions into the for_generics hash map first, to ensure
529 // that we don't end up with duplicate bounds (e.g., for<'b, 'b>)
530 for_generics.extend(p.generic_params.drain(..));
531 p.generic_params.extend(for_generics);
532 self.is_fn_trait(&p.trait_)
533 }
534 _ => false,
535 };
536
537 let poly_trait = b.get_poly_trait().expect("Cannot get poly trait");
538
539 if is_fn {
540 ty_to_fn
541 .entry(ty.clone())
542 .and_modify(|e| *e = (poly_trait.clone(), e.1.clone()))
543 .or_insert(((poly_trait.clone()), None));
544
545 ty_to_bounds.entry(ty.clone()).or_default();
546 } else {
547 ty_to_bounds.entry(ty.clone()).or_default().insert(b.clone());
548 }
549 }
550 }
551 WherePredicate::RegionPredicate { lifetime, bounds } => {
552 lifetime_to_bounds.entry(lifetime).or_default().extend(bounds);
553 }
554 WherePredicate::EqPredicate { lhs, rhs, bound_params } => {
555 match *lhs {
556 Type::QPath(box QPathData {
557 ref assoc,
558 ref self_type,
559 trait_: Some(ref trait_),
560 ..
561 }) => {
562 let ty = &*self_type;
563 let mut new_trait = trait_.clone();
564
565 if self.is_fn_trait(trait_) && assoc.name == sym::Output {
566 ty_to_fn
567 .entry(ty.clone())
568 .and_modify(|e| {
569 *e = (e.0.clone(), Some(rhs.ty().unwrap().clone()))
570 })
571 .or_insert((
572 PolyTrait {
573 trait_: trait_.clone(),
574 generic_params: Vec::new(),
575 },
576 Some(rhs.ty().unwrap().clone()),
577 ));
578 continue;
579 }
580
581 let args = &mut new_trait
582 .segments
583 .last_mut()
584 .expect("segments were empty")
585 .args;
586
587 match args {
588 // Convert something like '<T as Iterator::Item> = u8'
589 // to 'T: Iterator<Item=u8>'
590 GenericArgs::AngleBracketed { ref mut bindings, .. } => {
591 bindings.push(TypeBinding {
592 assoc: assoc.clone(),
593 kind: TypeBindingKind::Equality { term: *rhs },
594 });
595 }
596 GenericArgs::Parenthesized { .. } => {
597 existing_predicates.push(WherePredicate::EqPredicate {
598 lhs: lhs.clone(),
599 rhs,
600 bound_params,
601 });
602 continue; // If something other than a Fn ends up
603 // with parentheses, leave it alone
604 }
605 }
606
607 let bounds = ty_to_bounds.entry(ty.clone()).or_default();
608
609 bounds.insert(GenericBound::TraitBound(
610 PolyTrait { trait_: new_trait, generic_params: Vec::new() },
611 hir::TraitBoundModifier::None,
612 ));
613
614 // Remove any existing 'plain' bound (e.g., 'T: Iterator`) so
615 // that we don't see a
616 // duplicate bound like `T: Iterator + Iterator<Item=u8>`
617 // on the docs page.
618 bounds.remove(&GenericBound::TraitBound(
619 PolyTrait { trait_: trait_.clone(), generic_params: Vec::new() },
620 hir::TraitBoundModifier::None,
621 ));
622 // Avoid creating any new duplicate bounds later in the outer
623 // loop
624 ty_to_traits.entry(ty.clone()).or_default().insert(trait_.clone());
625 }
626 _ => panic!("Unexpected LHS {:?} for {:?}", lhs, item_def_id),
627 }
628 }
629 };
630 }
631
632 let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
633
634 existing_predicates.extend(final_bounds);
635
636 for param in generic_params.iter_mut() {
637 match param.kind {
638 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
639 // We never want something like `impl<T=Foo>`.
640 default.take();
641 let generic_ty = Type::Generic(param.name);
642 if !has_sized.contains(&generic_ty) {
643 bounds.insert(0, GenericBound::maybe_sized(self.cx));
644 }
645 }
646 GenericParamDefKind::Lifetime { .. } => {}
647 GenericParamDefKind::Const { ref mut default, .. } => {
648 // We never want something like `impl<const N: usize = 10>`
649 default.take();
650 }
651 }
652 }
653
654 self.sort_where_predicates(&mut existing_predicates);
655
656 Generics { params: generic_params, where_predicates: existing_predicates }
657 }
658
659 /// Ensure that the predicates are in a consistent order. The precise
660 /// ordering doesn't actually matter, but it's important that
661 /// a given set of predicates always appears in the same order -
662 /// both for visual consistency between 'rustdoc' runs, and to
663 /// make writing tests much easier
664 #[inline]
sort_where_predicates(&self, predicates: &mut [WherePredicate])665 fn sort_where_predicates(&self, predicates: &mut [WherePredicate]) {
666 // We should never have identical bounds - and if we do,
667 // they're visually identical as well. Therefore, using
668 // an unstable sort is fine.
669 self.unstable_debug_sort(predicates);
670 }
671
672 /// Ensure that the bounds are in a consistent order. The precise
673 /// ordering doesn't actually matter, but it's important that
674 /// a given set of bounds always appears in the same order -
675 /// both for visual consistency between 'rustdoc' runs, and to
676 /// make writing tests much easier
677 #[inline]
sort_where_bounds(&self, bounds: &mut Vec<GenericBound>)678 fn sort_where_bounds(&self, bounds: &mut Vec<GenericBound>) {
679 // We should never have identical bounds - and if we do,
680 // they're visually identical as well. Therefore, using
681 // an unstable sort is fine.
682 self.unstable_debug_sort(bounds);
683 }
684
685 /// This might look horrendously hacky, but it's actually not that bad.
686 ///
687 /// For performance reasons, we use several different FxHashMaps
688 /// in the process of computing the final set of where predicates.
689 /// However, the iteration order of a HashMap is completely unspecified.
690 /// In fact, the iteration of an FxHashMap can even vary between platforms,
691 /// since FxHasher has different behavior for 32-bit and 64-bit platforms.
692 ///
693 /// Obviously, it's extremely undesirable for documentation rendering
694 /// to be dependent on the platform it's run on. Apart from being confusing
695 /// to end users, it makes writing tests much more difficult, as predicates
696 /// can appear in any order in the final result.
697 ///
698 /// To solve this problem, we sort WherePredicates and GenericBounds
699 /// by their Debug string. The thing to keep in mind is that we don't really
700 /// care what the final order is - we're synthesizing an impl or bound
701 /// ourselves, so any order can be considered equally valid. By sorting the
702 /// predicates and bounds, however, we ensure that for a given codebase, all
703 /// auto-trait impls always render in exactly the same way.
704 ///
705 /// Using the Debug implementation for sorting prevents us from needing to
706 /// write quite a bit of almost entirely useless code (e.g., how should two
707 /// Types be sorted relative to each other). It also allows us to solve the
708 /// problem for both WherePredicates and GenericBounds at the same time. This
709 /// approach is probably somewhat slower, but the small number of items
710 /// involved (impls rarely have more than a few bounds) means that it
711 /// shouldn't matter in practice.
unstable_debug_sort<T: Debug>(&self, vec: &mut [T])712 fn unstable_debug_sort<T: Debug>(&self, vec: &mut [T]) {
713 vec.sort_by_cached_key(|x| format!("{:?}", x))
714 }
715
is_fn_trait(&self, path: &Path) -> bool716 fn is_fn_trait(&self, path: &Path) -> bool {
717 let tcx = self.cx.tcx;
718 let did = path.def_id();
719 did == tcx.require_lang_item(LangItem::Fn, None)
720 || did == tcx.require_lang_item(LangItem::FnMut, None)
721 || did == tcx.require_lang_item(LangItem::FnOnce, None)
722 }
723 }
724
region_name(region: Region<'_>) -> Option<Symbol>725 fn region_name(region: Region<'_>) -> Option<Symbol> {
726 match *region {
727 ty::ReEarlyBound(r) => Some(r.name),
728 _ => None,
729 }
730 }
731
732 /// Replaces all [`ty::RegionVid`]s in a type with [`ty::Region`]s, using the provided map.
733 struct RegionReplacer<'a, 'tcx> {
734 vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
735 tcx: TyCtxt<'tcx>,
736 }
737
738 impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for RegionReplacer<'a, 'tcx> {
interner(&self) -> TyCtxt<'tcx>739 fn interner(&self) -> TyCtxt<'tcx> {
740 self.tcx
741 }
742
fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx>743 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
744 match *r {
745 // These are the regions that can be seen in the AST.
746 ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned().unwrap_or(r),
747 ty::ReEarlyBound(_) | ty::ReStatic | ty::ReLateBound(..) | ty::ReError(_) => r,
748 r => bug!("unexpected region: {r:?}"),
749 }
750 }
751 }
752