1 use rustc_ast::ast::Attribute;
2 use rustc_errors::Applicability;
3 use rustc_hir::def_id::{DefIdSet, LocalDefId};
4 use rustc_hir::{self as hir, def::Res, QPath};
5 use rustc_lint::{LateContext, LintContext};
7 lint::in_external_macro,
10 use rustc_span::{sym, Span, Symbol};
12 use clippy_utils::attrs::is_proc_macro;
13 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_then};
14 use clippy_utils::source::snippet_opt;
15 use clippy_utils::ty::is_must_use_ty;
16 use clippy_utils::visitors::for_each_expr;
17 use clippy_utils::{return_ty, trait_ref_of_method};
19 use core::ops::ControlFlow;
21 use super::{DOUBLE_MUST_USE, MUST_USE_CANDIDATE, MUST_USE_UNIT};
23 pub(super) fn check_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
24 let attrs = cx.tcx.hir().attrs(item.hir_id());
25 let attr = cx.tcx.get_attr(item.owner_id.to_def_id(), sym::must_use);
26 if let hir::ItemKind::Fn(ref sig, _generics, ref body_id) = item.kind {
27 let is_public = cx.effective_visibilities.is_exported(item.owner_id.def_id);
28 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
29 if let Some(attr) = attr {
30 check_needless_must_use(cx, sig.decl, item.hir_id(), item.span, fn_header_span, attr);
31 } else if is_public && !is_proc_macro(cx.sess(), attrs) && !attrs.iter().any(|a| a.has_name(sym::no_mangle)) {
32 check_must_use_candidate(
35 cx.tcx.hir().body(*body_id),
38 item.span.with_hi(sig.decl.output.span().hi()),
39 "this function could have a `#[must_use]` attribute",
45 pub(super) fn check_impl_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'_>) {
46 if let hir::ImplItemKind::Fn(ref sig, ref body_id) = item.kind {
47 let is_public = cx.effective_visibilities.is_exported(item.owner_id.def_id);
48 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
49 let attrs = cx.tcx.hir().attrs(item.hir_id());
50 let attr = cx.tcx.get_attr(item.owner_id.to_def_id(), sym::must_use);
51 if let Some(attr) = attr {
52 check_needless_must_use(cx, sig.decl, item.hir_id(), item.span, fn_header_span, attr);
54 && !is_proc_macro(cx.sess(), attrs)
55 && trait_ref_of_method(cx, item.owner_id.def_id).is_none()
57 check_must_use_candidate(
60 cx.tcx.hir().body(*body_id),
63 item.span.with_hi(sig.decl.output.span().hi()),
64 "this method could have a `#[must_use]` attribute",
70 pub(super) fn check_trait_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'_>) {
71 if let hir::TraitItemKind::Fn(ref sig, ref eid) = item.kind {
72 let is_public = cx.effective_visibilities.is_exported(item.owner_id.def_id);
73 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
75 let attrs = cx.tcx.hir().attrs(item.hir_id());
76 let attr = cx.tcx.get_attr(item.owner_id.to_def_id(), sym::must_use);
77 if let Some(attr) = attr {
78 check_needless_must_use(cx, sig.decl, item.hir_id(), item.span, fn_header_span, attr);
79 } else if let hir::TraitFn::Provided(eid) = *eid {
80 let body = cx.tcx.hir().body(eid);
81 if attr.is_none() && is_public && !is_proc_macro(cx.sess(), attrs) {
82 check_must_use_candidate(
88 item.span.with_hi(sig.decl.output.span().hi()),
89 "this method could have a `#[must_use]` attribute",
96 fn check_needless_must_use(
98 decl: &hir::FnDecl<'_>,
101 fn_header_span: Span,
104 if in_external_macro(cx.sess(), item_span) {
107 if returns_unit(decl) {
112 "this unit-returning function has a `#[must_use]` attribute",
114 diag.span_suggestion(attr.span, "remove the attribute", "", Applicability::MachineApplicable);
117 } else if attr.value_str().is_none() && is_must_use_ty(cx, return_ty(cx, item_id)) {
122 "this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]`",
124 "either add some descriptive text or remove the attribute",
129 fn check_must_use_candidate<'tcx>(
130 cx: &LateContext<'tcx>,
131 decl: &'tcx hir::FnDecl<'_>,
132 body: &'tcx hir::Body<'_>,
138 if has_mutable_arg(cx, body)
139 || mutates_static(cx, body)
140 || in_external_macro(cx.sess(), item_span)
141 || returns_unit(decl)
142 || !cx.effective_visibilities.is_exported(item_id)
143 || is_must_use_ty(cx, return_ty(cx, cx.tcx.hir().local_def_id_to_hir_id(item_id)))
147 span_lint_and_then(cx, MUST_USE_CANDIDATE, fn_span, msg, |diag| {
148 if let Some(snippet) = snippet_opt(cx, fn_span) {
149 diag.span_suggestion(
152 format!("#[must_use] {snippet}"),
153 Applicability::MachineApplicable,
159 fn returns_unit(decl: &hir::FnDecl<'_>) -> bool {
161 hir::FnRetTy::DefaultReturn(_) => true,
162 hir::FnRetTy::Return(ty) => match ty.kind {
163 hir::TyKind::Tup(tys) => tys.is_empty(),
164 hir::TyKind::Never => true,
170 fn has_mutable_arg(cx: &LateContext<'_>, body: &hir::Body<'_>) -> bool {
171 let mut tys = DefIdSet::default();
172 body.params.iter().any(|param| is_mutable_pat(cx, param.pat, &mut tys))
175 fn is_mutable_pat(cx: &LateContext<'_>, pat: &hir::Pat<'_>, tys: &mut DefIdSet) -> bool {
176 if let hir::PatKind::Wild = pat.kind {
177 return false; // ignore `_` patterns
179 if cx.tcx.has_typeck_results(pat.hir_id.owner.to_def_id()) {
180 is_mutable_ty(cx, cx.tcx.typeck(pat.hir_id.owner.def_id).pat_ty(pat), tys)
186 static KNOWN_WRAPPER_TYS: &[Symbol] = &[sym::Rc, sym::Arc];
188 fn is_mutable_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, tys: &mut DefIdSet) -> bool {
190 // primitive types are never mutable
191 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => false,
192 ty::Adt(adt, substs) => {
193 tys.insert(adt.did()) && !ty.is_freeze(cx.tcx, cx.param_env)
196 .any(|&sym| cx.tcx.is_diagnostic_item(sym, adt.did()))
197 && substs.types().any(|ty| is_mutable_ty(cx, ty, tys))
199 ty::Tuple(substs) => substs.iter().any(|ty| is_mutable_ty(cx, ty, tys)),
200 ty::Array(ty, _) | ty::Slice(ty) => is_mutable_ty(cx, ty, tys),
201 ty::RawPtr(ty::TypeAndMut { ty, mutbl }) | ty::Ref(_, ty, mutbl) => {
202 mutbl == hir::Mutability::Mut || is_mutable_ty(cx, ty, tys)
204 // calling something constitutes a side effect, so return true on all callables
205 // also never calls need not be used, so return true for them, too
210 fn is_mutated_static(e: &hir::Expr<'_>) -> bool {
211 use hir::ExprKind::{Field, Index, Path};
214 Path(QPath::Resolved(_, path)) => !matches!(path.res, Res::Local(_)),
216 Field(inner, _) | Index(inner, _) => is_mutated_static(inner),
221 fn mutates_static<'tcx>(cx: &LateContext<'tcx>, body: &'tcx hir::Body<'_>) -> bool {
222 for_each_expr(body.value, |e| {
223 use hir::ExprKind::{AddrOf, Assign, AssignOp, Call, MethodCall};
227 let mut tys = DefIdSet::default();
229 if cx.tcx.has_typeck_results(arg.hir_id.owner.to_def_id())
230 && is_mutable_ty(cx, cx.tcx.typeck(arg.hir_id.owner.def_id).expr_ty(arg), &mut tys)
231 && is_mutated_static(arg)
233 return ControlFlow::Break(());
237 ControlFlow::Continue(())
239 MethodCall(_, receiver, args, _) => {
240 let mut tys = DefIdSet::default();
241 for arg in std::iter::once(receiver).chain(args.iter()) {
242 if cx.tcx.has_typeck_results(arg.hir_id.owner.to_def_id())
243 && is_mutable_ty(cx, cx.tcx.typeck(arg.hir_id.owner.def_id).expr_ty(arg), &mut tys)
244 && is_mutated_static(arg)
246 return ControlFlow::Break(());
250 ControlFlow::Continue(())
252 Assign(target, ..) | AssignOp(_, target, _) | AddrOf(_, hir::Mutability::Mut, target)
253 if is_mutated_static(target) =>
255 ControlFlow::Break(())
257 _ => ControlFlow::Continue(()),