1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::ty::is_must_use_ty;
3 use clippy_utils::{nth_arg, return_ty};
4 use rustc_hir::def_id::LocalDefId;
5 use rustc_hir::intravisit::FnKind;
6 use rustc_hir::{Body, FnDecl, HirId, TraitItem, TraitItemKind};
7 use rustc_lint::{LateContext, LateLintPass, LintContext};
8 use rustc_middle::lint::in_external_macro;
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 use rustc_span::{sym, Span};
12 declare_clippy_lint! {
14 /// This lint warns when a method returning `Self` doesn't have the `#[must_use]` attribute.
16 /// ### Why is this bad?
17 /// Methods returning `Self` often create new values, having the `#[must_use]` attribute
18 /// prevents users from "forgetting" to use the newly created value.
20 /// The `#[must_use]` attribute can be added to the type itself to ensure that instances
21 /// are never forgotten. Functions returning a type marked with `#[must_use]` will not be
22 /// linted, as the usage is already enforced by the type attribute.
25 /// This lint is only applied on methods taking a `self` argument. It would be mostly noise
26 /// if it was added on constructors for example.
32 /// // Missing attribute
33 /// pub fn bar(&self) -> Self {
42 /// // It's better to have the `#[must_use]` attribute on the method like this:
46 /// pub fn bar(&self) -> Self {
53 /// // Or on the type definition like this:
57 /// pub fn bar(&self) -> Self {
63 #[clippy::version = "1.59.0"]
64 pub RETURN_SELF_NOT_MUST_USE,
66 "missing `#[must_use]` annotation on a method returning `Self`"
69 declare_lint_pass!(ReturnSelfNotMustUse => [RETURN_SELF_NOT_MUST_USE]);
71 fn check_method(cx: &LateContext<'_>, decl: &FnDecl<'_>, fn_def: LocalDefId, span: Span, hir_id: HirId) {
73 // If it comes from an external macro, better ignore it.
74 if !in_external_macro(cx.sess(), span);
75 if decl.implicit_self.has_implicit_self();
76 // We only show this warning for public exported methods.
77 if cx.effective_visibilities.is_exported(fn_def);
78 // We don't want to emit this lint if the `#[must_use]` attribute is already there.
79 if !cx.tcx.hir().attrs(hir_id).iter().any(|attr| attr.has_name(sym::must_use));
80 if cx.tcx.visibility(fn_def.to_def_id()).is_public();
81 let ret_ty = return_ty(cx, hir_id);
82 let self_arg = nth_arg(cx, hir_id, 0);
83 // If `Self` has the same type as the returned type, then we want to warn.
85 // For this check, we don't want to remove the reference on the returned type because if
86 // there is one, we shouldn't emit a warning!
87 if self_arg.peel_refs() == ret_ty;
88 // If `Self` is already marked as `#[must_use]`, no need for the attribute here.
89 if !is_must_use_ty(cx, ret_ty);
94 RETURN_SELF_NOT_MUST_USE,
96 "missing `#[must_use]` attribute on a method returning `Self`",
98 "consider adding the `#[must_use]` attribute to the method or directly to the `Self` type"
104 impl<'tcx> LateLintPass<'tcx> for ReturnSelfNotMustUse {
107 cx: &LateContext<'tcx>,
109 decl: &'tcx FnDecl<'tcx>,
115 // We are only interested in methods, not in functions or associated functions.
116 if matches!(kind, FnKind::Method(_, _));
117 if let Some(fn_def) = cx.tcx.hir().opt_local_def_id(hir_id);
118 if let Some(impl_def) = cx.tcx.impl_of_method(fn_def.to_def_id());
119 // We don't want this method to be te implementation of a trait because the
120 // `#[must_use]` should be put on the trait definition directly.
121 if cx.tcx.trait_id_of_impl(impl_def).is_none();
124 check_method(cx, decl, fn_def, span, hir_id);
129 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
130 if let TraitItemKind::Fn(ref sig, _) = item.kind {
131 check_method(cx, sig.decl, item.owner_id.def_id, item.span, item.hir_id());