1 use clippy_utils::ty::is_must_use_ty;
2 use clippy_utils::{diagnostics::span_lint, nth_arg, return_ty};
3 use rustc_hir::def_id::LocalDefId;
4 use rustc_hir::intravisit::FnKind;
5 use rustc_hir::{Body, FnDecl, HirId, TraitItem, TraitItemKind};
6 use rustc_lint::{LateContext, LateLintPass, LintContext};
7 use rustc_middle::lint::in_external_macro;
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 use rustc_span::{sym, Span};
11 declare_clippy_lint! {
13 /// This lint warns when a method returning `Self` doesn't have the `#[must_use]` attribute.
15 /// ### Why is this bad?
16 /// It prevents to "forget" to use the newly created value.
19 /// This lint is only applied on methods taking a `self` argument. It would be mostly noise
20 /// if it was added on constructors for example.
28 /// pub fn bar(&self) -> Self {
34 /// pub fn foo(&self) -> Self {
39 #[clippy::version = "1.59.0"]
40 pub RETURN_SELF_NOT_MUST_USE,
42 "missing `#[must_use]` annotation on a method returning `Self`"
45 declare_lint_pass!(ReturnSelfNotMustUse => [RETURN_SELF_NOT_MUST_USE]);
47 fn check_method(cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'tcx>, fn_def: LocalDefId, span: Span, hir_id: HirId) {
49 // If it comes from an external macro, better ignore it.
50 if !in_external_macro(cx.sess(), span);
51 if decl.implicit_self.has_implicit_self();
52 // We only show this warning for public exported methods.
53 if cx.access_levels.is_exported(fn_def);
54 // We don't want to emit this lint if the `#[must_use]` attribute is already there.
55 if !cx.tcx.hir().attrs(hir_id).iter().any(|attr| attr.has_name(sym::must_use));
56 if cx.tcx.visibility(fn_def.to_def_id()).is_public();
57 let ret_ty = return_ty(cx, hir_id);
58 let self_arg = nth_arg(cx, hir_id, 0);
59 // If `Self` has the same type as the returned type, then we want to warn.
61 // For this check, we don't want to remove the reference on the returned type because if
62 // there is one, we shouldn't emit a warning!
63 if self_arg.peel_refs() == ret_ty;
64 // If `Self` is already marked as `#[must_use]`, no need for the attribute here.
65 if !is_must_use_ty(cx, ret_ty);
70 RETURN_SELF_NOT_MUST_USE,
72 "missing `#[must_use]` attribute on a method returning `Self`",
78 impl<'tcx> LateLintPass<'tcx> for ReturnSelfNotMustUse {
81 cx: &LateContext<'tcx>,
83 decl: &'tcx FnDecl<'tcx>,
89 // We are only interested in methods, not in functions or associated functions.
90 if matches!(kind, FnKind::Method(_, _, _));
91 if let Some(fn_def) = cx.tcx.hir().opt_local_def_id(hir_id);
92 if let Some(impl_def) = cx.tcx.impl_of_method(fn_def.to_def_id());
93 // We don't want this method to be te implementation of a trait because the
94 // `#[must_use]` should be put on the trait definition directly.
95 if cx.tcx.trait_id_of_impl(impl_def).is_none();
98 check_method(cx, decl, fn_def, span, hir_id);
103 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
104 if let TraitItemKind::Fn(ref sig, _) = item.kind {
105 check_method(cx, sig.decl, item.def_id, item.span, item.hir_id());