1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::last_path_segment;
3 use clippy_utils::source::snippet_with_context;
4 use clippy_utils::{match_def_path, paths};
5 use rustc_errors::Applicability;
6 use rustc_hir::{def, Expr, ExprKind, GenericArg, QPath, TyKind};
7 use rustc_lint::{LateContext, LateLintPass};
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 use rustc_span::SyntaxContext;
10
11 declare_clippy_lint! {
12 /// ### What it does
13 /// It checks for `std::iter::Empty::default()` and suggests replacing it with
14 /// `std::iter::empty()`.
15 /// ### Why is this bad?
16 /// `std::iter::empty()` is the more idiomatic way.
17 /// ### Example
18 /// ```rust
19 /// let _ = std::iter::Empty::<usize>::default();
20 /// let iter: std::iter::Empty<usize> = std::iter::Empty::default();
21 /// ```
22 /// Use instead:
23 /// ```rust
24 /// let _ = std::iter::empty::<usize>();
25 /// let iter: std::iter::Empty<usize> = std::iter::empty();
26 /// ```
27 #[clippy::version = "1.64.0"]
28 pub DEFAULT_INSTEAD_OF_ITER_EMPTY,
29 style,
30 "check `std::iter::Empty::default()` and replace with `std::iter::empty()`"
31 }
32 declare_lint_pass!(DefaultIterEmpty => [DEFAULT_INSTEAD_OF_ITER_EMPTY]);
33
34 impl<'tcx> LateLintPass<'tcx> for DefaultIterEmpty {
check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>)35 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
36 if let ExprKind::Call(iter_expr, []) = &expr.kind
37 && let ExprKind::Path(QPath::TypeRelative(ty, _)) = &iter_expr.kind
38 && let TyKind::Path(ty_path) = &ty.kind
39 && let QPath::Resolved(None, path) = ty_path
40 && let def::Res::Def(_, def_id) = &path.res
41 && match_def_path(cx, *def_id, &paths::ITER_EMPTY)
42 && let ctxt = expr.span.ctxt()
43 && ty.span.ctxt() == ctxt
44 {
45 let mut applicability = Applicability::MachineApplicable;
46 let sugg = make_sugg(cx, ty_path, ctxt, &mut applicability);
47 span_lint_and_sugg(
48 cx,
49 DEFAULT_INSTEAD_OF_ITER_EMPTY,
50 expr.span,
51 "`std::iter::empty()` is the more idiomatic way",
52 "try",
53 sugg,
54 applicability,
55 );
56 }
57 }
58 }
59
make_sugg( cx: &LateContext<'_>, ty_path: &rustc_hir::QPath<'_>, ctxt: SyntaxContext, applicability: &mut Applicability, ) -> String60 fn make_sugg(
61 cx: &LateContext<'_>,
62 ty_path: &rustc_hir::QPath<'_>,
63 ctxt: SyntaxContext,
64 applicability: &mut Applicability,
65 ) -> String {
66 if let Some(last) = last_path_segment(ty_path).args
67 && let Some(iter_ty) = last.args.iter().find_map(|arg| match arg {
68 GenericArg::Type(ty) => Some(ty),
69 _ => None,
70 })
71 {
72 format!("std::iter::empty::<{}>()", snippet_with_context(cx, iter_ty.span, ctxt, "..", applicability).0)
73 } else {
74 "std::iter::empty()".to_owned()
75 }
76 }
77