2 attr_by_name, attrs::is_proc_macro, is_must_use_ty, is_trait_impl_item, iter_input_pats, match_def_path,
3 must_use_attr, qpath_res, return_ty, snippet, snippet_opt, span_lint, span_lint_and_help, span_lint_and_then,
4 trait_ref_of_method, type_is_unsafe_function,
6 use rustc_ast::ast::Attribute;
7 use rustc_data_structures::fx::FxHashSet;
8 use rustc_errors::Applicability;
10 use rustc_hir::intravisit;
11 use rustc_hir::{def::Res, def_id::DefId};
12 use rustc_lint::{LateContext, LateLintPass, LintContext};
13 use rustc_middle::hir::map::Map;
14 use rustc_middle::lint::in_external_macro;
15 use rustc_middle::ty::{self, Ty};
16 use rustc_session::{declare_tool_lint, impl_lint_pass};
17 use rustc_span::source_map::Span;
18 use rustc_target::spec::abi::Abi;
20 declare_clippy_lint! {
21 /// **What it does:** Checks for functions with too many parameters.
23 /// **Why is this bad?** Functions with lots of parameters are considered bad
24 /// style and reduce readability (“what does the 5th parameter mean?”). Consider
25 /// grouping some parameters into a new type.
27 /// **Known problems:** None.
32 /// fn foo(x: u32, y: u32, name: &str, c: Color, w: f32, h: f32, a: f32, b: f32) {
36 pub TOO_MANY_ARGUMENTS,
38 "functions with too many arguments"
41 declare_clippy_lint! {
42 /// **What it does:** Checks for functions with a large amount of lines.
44 /// **Why is this bad?** Functions with a lot of lines are harder to understand
45 /// due to having to look at a larger amount of code to understand what the
46 /// function is doing. Consider splitting the body of the function into
47 /// multiple functions.
49 /// **Known problems:** None.
53 /// fn im_too_long() {
55 /// // ... 100 more LoC
61 "functions with too many lines"
64 declare_clippy_lint! {
65 /// **What it does:** Checks for public functions that dereference raw pointer
66 /// arguments but are not marked unsafe.
68 /// **Why is this bad?** The function should probably be marked `unsafe`, since
69 /// for an arbitrary raw pointer, there is no way of telling for sure if it is
72 /// **Known problems:**
74 /// * It does not check functions recursively so if the pointer is passed to a
75 /// private non-`unsafe` function which does the dereferencing, the lint won't
77 /// * It only checks for arguments whose type are raw pointers, not raw pointers
78 /// got from an argument in some other way (`fn foo(bar: &[*const u8])` or
79 /// `some_argument.get_raw_ptr()`).
83 /// pub fn foo(x: *const u8) {
84 /// println!("{}", unsafe { *x });
87 pub NOT_UNSAFE_PTR_ARG_DEREF,
89 "public functions dereferencing raw pointer arguments but not marked `unsafe`"
92 declare_clippy_lint! {
93 /// **What it does:** Checks for a [`#[must_use]`] attribute on
94 /// unit-returning functions and methods.
96 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
98 /// **Why is this bad?** Unit values are useless. The attribute is likely
99 /// a remnant of a refactoring that removed the return type.
101 /// **Known problems:** None.
110 "`#[must_use]` attribute on a unit-returning function / method"
113 declare_clippy_lint! {
114 /// **What it does:** Checks for a [`#[must_use]`] attribute without
115 /// further information on functions and methods that return a type already
116 /// marked as `#[must_use]`.
118 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
120 /// **Why is this bad?** The attribute isn't needed. Not using the result
121 /// will already be reported. Alternatively, one can add some text to the
122 /// attribute to improve the lint message.
124 /// **Known problems:** None.
129 /// fn double_must_use() -> Result<(), ()> {
130 /// unimplemented!();
135 "`#[must_use]` attribute on a `#[must_use]`-returning function / method"
138 declare_clippy_lint! {
139 /// **What it does:** Checks for public functions that have no
140 /// [`#[must_use]`] attribute, but return something not already marked
141 /// must-use, have no mutable arg and mutate no statics.
143 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
145 /// **Why is this bad?** Not bad at all, this lint just shows places where
146 /// you could add the attribute.
148 /// **Known problems:** The lint only checks the arguments for mutable
149 /// types without looking if they are actually changed. On the other hand,
150 /// it also ignores a broad range of potentially interesting side effects,
151 /// because we cannot decide whether the programmer intends the function to
152 /// be called for the side effect or the result. Expect many false
153 /// positives. At least we don't lint if the result type is unit or already
158 /// // this could be annotated with `#[must_use]`.
159 /// fn id<T>(t: T) -> T { t }
161 pub MUST_USE_CANDIDATE,
163 "function or method that could take a `#[must_use]` attribute"
166 #[derive(Copy, Clone)]
167 pub struct Functions {
173 pub fn new(threshold: u64, max_lines: u64) -> Self {
174 Self { threshold, max_lines }
178 impl_lint_pass!(Functions => [
181 NOT_UNSAFE_PTR_ARG_DEREF,
187 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Functions {
190 cx: &LateContext<'a, 'tcx>,
191 kind: intravisit::FnKind<'tcx>,
192 decl: &'tcx hir::FnDecl<'_>,
193 body: &'tcx hir::Body<'_>,
197 let unsafety = match kind {
198 intravisit::FnKind::ItemFn(_, _, hir::FnHeader { unsafety, .. }, _, _) => unsafety,
199 intravisit::FnKind::Method(_, sig, _, _) => sig.header.unsafety,
200 intravisit::FnKind::Closure(_) => return,
203 // don't warn for implementations, it's not their fault
204 if !is_trait_impl_item(cx, hir_id) {
205 // don't lint extern functions decls, it's not their fault either
207 intravisit::FnKind::Method(
210 header: hir::FnHeader { abi: Abi::Rust, .. },
216 | intravisit::FnKind::ItemFn(_, _, hir::FnHeader { abi: Abi::Rust, .. }, _, _) => {
217 self.check_arg_number(cx, decl, span.with_hi(decl.output.span().hi()))
223 Self::check_raw_ptr(cx, unsafety, decl, body, hir_id);
224 self.check_line_number(cx, span, body);
227 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'_>) {
228 let attr = must_use_attr(&item.attrs);
229 if let hir::ItemKind::Fn(ref sig, ref _generics, ref body_id) = item.kind {
230 if let Some(attr) = attr {
231 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
232 check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
235 if cx.access_levels.is_exported(item.hir_id)
236 && !is_proc_macro(&item.attrs)
237 && attr_by_name(&item.attrs, "no_mangle").is_none()
239 check_must_use_candidate(
242 cx.tcx.hir().body(*body_id),
245 item.span.with_hi(sig.decl.output.span().hi()),
246 "this function could have a `#[must_use]` attribute",
252 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::ImplItem<'_>) {
253 if let hir::ImplItemKind::Fn(ref sig, ref body_id) = item.kind {
254 let attr = must_use_attr(&item.attrs);
255 if let Some(attr) = attr {
256 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
257 check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
258 } else if cx.access_levels.is_exported(item.hir_id)
259 && !is_proc_macro(&item.attrs)
260 && trait_ref_of_method(cx, item.hir_id).is_none()
262 check_must_use_candidate(
265 cx.tcx.hir().body(*body_id),
268 item.span.with_hi(sig.decl.output.span().hi()),
269 "this method could have a `#[must_use]` attribute",
275 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::TraitItem<'_>) {
276 if let hir::TraitItemKind::Fn(ref sig, ref eid) = item.kind {
277 // don't lint extern functions decls, it's not their fault
278 if sig.header.abi == Abi::Rust {
279 self.check_arg_number(cx, &sig.decl, item.span.with_hi(sig.decl.output.span().hi()));
282 let attr = must_use_attr(&item.attrs);
283 if let Some(attr) = attr {
284 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
285 check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
287 if let hir::TraitFn::Provided(eid) = *eid {
288 let body = cx.tcx.hir().body(eid);
289 Self::check_raw_ptr(cx, sig.header.unsafety, &sig.decl, body, item.hir_id);
291 if attr.is_none() && cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
292 check_must_use_candidate(
298 item.span.with_hi(sig.decl.output.span().hi()),
299 "this method could have a `#[must_use]` attribute",
307 impl<'a, 'tcx> Functions {
308 fn check_arg_number(self, cx: &LateContext<'_, '_>, decl: &hir::FnDecl<'_>, fn_span: Span) {
309 let args = decl.inputs.len() as u64;
310 if args > self.threshold {
315 &format!("this function has too many arguments ({}/{})", args, self.threshold),
320 fn check_line_number(self, cx: &LateContext<'_, '_>, span: Span, body: &'tcx hir::Body<'_>) {
321 if in_external_macro(cx.sess(), span) {
325 let code_snippet = snippet(cx, body.value.span, "..");
326 let mut line_count: u64 = 0;
327 let mut in_comment = false;
328 let mut code_in_line;
330 // Skip the surrounding function decl.
331 let start_brace_idx = code_snippet.find('{').map_or(0, |i| i + 1);
332 let end_brace_idx = code_snippet.rfind('}').unwrap_or_else(|| code_snippet.len());
333 let function_lines = code_snippet[start_brace_idx..end_brace_idx].lines();
335 for mut line in function_lines {
336 code_in_line = false;
338 line = line.trim_start();
343 match line.find("*/") {
345 line = &line[i + 2..];
352 let multi_idx = line.find("/*").unwrap_or_else(|| line.len());
353 let single_idx = line.find("//").unwrap_or_else(|| line.len());
354 code_in_line |= multi_idx > 0 && single_idx > 0;
355 // Implies multi_idx is below line.len()
356 if multi_idx < single_idx {
357 line = &line[multi_idx + 2..];
369 if line_count > self.max_lines {
370 span_lint(cx, TOO_MANY_LINES, span, "This function has a large number of lines.")
375 cx: &LateContext<'a, 'tcx>,
376 unsafety: hir::Unsafety,
377 decl: &'tcx hir::FnDecl<'_>,
378 body: &'tcx hir::Body<'_>,
381 let expr = &body.value;
382 if unsafety == hir::Unsafety::Normal && cx.access_levels.is_exported(hir_id) {
383 let raw_ptrs = iter_input_pats(decl, body)
384 .zip(decl.inputs.iter())
385 .filter_map(|(arg, ty)| raw_ptr_arg(arg, ty))
386 .collect::<FxHashSet<_>>();
388 if !raw_ptrs.is_empty() {
389 let tables = cx.tcx.body_tables(body.id());
390 let mut v = DerefVisitor {
396 intravisit::walk_expr(&mut v, expr);
402 fn check_needless_must_use(
403 cx: &LateContext<'_, '_>,
404 decl: &hir::FnDecl<'_>,
407 fn_header_span: Span,
410 if in_external_macro(cx.sess(), item_span) {
413 if returns_unit(decl) {
418 "this unit-returning function has a `#[must_use]` attribute",
420 diag.span_suggestion(
422 "remove the attribute",
424 Applicability::MachineApplicable,
428 } else if !attr.is_value_str() && is_must_use_ty(cx, return_ty(cx, item_id)) {
433 "this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]`",
435 "either add some descriptive text or remove the attribute",
440 fn check_must_use_candidate<'a, 'tcx>(
441 cx: &LateContext<'a, 'tcx>,
442 decl: &'tcx hir::FnDecl<'_>,
443 body: &'tcx hir::Body<'_>,
449 if has_mutable_arg(cx, body)
450 || mutates_static(cx, body)
451 || in_external_macro(cx.sess(), item_span)
452 || returns_unit(decl)
453 || !cx.access_levels.is_exported(item_id)
454 || is_must_use_ty(cx, return_ty(cx, item_id))
458 span_lint_and_then(cx, MUST_USE_CANDIDATE, fn_span, msg, |diag| {
459 if let Some(snippet) = snippet_opt(cx, fn_span) {
460 diag.span_suggestion(
463 format!("#[must_use] {}", snippet),
464 Applicability::MachineApplicable,
470 fn returns_unit(decl: &hir::FnDecl<'_>) -> bool {
472 hir::FnRetTy::DefaultReturn(_) => true,
473 hir::FnRetTy::Return(ref ty) => match ty.kind {
474 hir::TyKind::Tup(ref tys) => tys.is_empty(),
475 hir::TyKind::Never => true,
481 fn has_mutable_arg(cx: &LateContext<'_, '_>, body: &hir::Body<'_>) -> bool {
482 let mut tys = FxHashSet::default();
483 body.params.iter().any(|param| is_mutable_pat(cx, ¶m.pat, &mut tys))
486 fn is_mutable_pat(cx: &LateContext<'_, '_>, pat: &hir::Pat<'_>, tys: &mut FxHashSet<DefId>) -> bool {
487 if let hir::PatKind::Wild = pat.kind {
488 return false; // ignore `_` patterns
490 let def_id = pat.hir_id.owner.to_def_id();
491 if cx.tcx.has_typeck_tables(def_id) {
492 is_mutable_ty(cx, &cx.tcx.typeck_tables_of(def_id).pat_ty(pat), pat.span, tys)
498 static KNOWN_WRAPPER_TYS: &[&[&str]] = &[&["alloc", "rc", "Rc"], &["std", "sync", "Arc"]];
500 fn is_mutable_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>, span: Span, tys: &mut FxHashSet<DefId>) -> bool {
502 // primitive types are never mutable
503 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => false,
504 ty::Adt(ref adt, ref substs) => {
505 tys.insert(adt.did) && !ty.is_freeze(cx.tcx, cx.param_env, span)
506 || KNOWN_WRAPPER_TYS.iter().any(|path| match_def_path(cx, adt.did, path))
507 && substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys))
509 ty::Tuple(ref substs) => substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys)),
510 ty::Array(ty, _) | ty::Slice(ty) => is_mutable_ty(cx, ty, span, tys),
511 ty::RawPtr(ty::TypeAndMut { ty, mutbl }) | ty::Ref(_, ty, mutbl) => {
512 mutbl == hir::Mutability::Mut || is_mutable_ty(cx, ty, span, tys)
514 // calling something constitutes a side effect, so return true on all callables
515 // also never calls need not be used, so return true for them, too
520 fn raw_ptr_arg(arg: &hir::Param<'_>, ty: &hir::Ty<'_>) -> Option<hir::HirId> {
521 if let (&hir::PatKind::Binding(_, id, _, _), &hir::TyKind::Ptr(_)) = (&arg.pat.kind, &ty.kind) {
528 struct DerefVisitor<'a, 'tcx> {
529 cx: &'a LateContext<'a, 'tcx>,
530 ptrs: FxHashSet<hir::HirId>,
531 tables: &'a ty::TypeckTables<'tcx>,
534 impl<'a, 'tcx> intravisit::Visitor<'tcx> for DerefVisitor<'a, 'tcx> {
535 type Map = Map<'tcx>;
537 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
539 hir::ExprKind::Call(ref f, args) => {
540 let ty = self.tables.expr_ty(f);
542 if type_is_unsafe_function(self.cx, ty) {
548 hir::ExprKind::MethodCall(_, _, args) => {
549 let def_id = self.tables.type_dependent_def_id(expr.hir_id).unwrap();
550 let base_type = self.cx.tcx.type_of(def_id);
552 if type_is_unsafe_function(self.cx, base_type) {
558 hir::ExprKind::Unary(hir::UnOp::UnDeref, ref ptr) => self.check_arg(ptr),
562 intravisit::walk_expr(self, expr);
565 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
566 intravisit::NestedVisitorMap::None
570 impl<'a, 'tcx> DerefVisitor<'a, 'tcx> {
571 fn check_arg(&self, ptr: &hir::Expr<'_>) {
572 if let hir::ExprKind::Path(ref qpath) = ptr.kind {
573 if let Res::Local(id) = qpath_res(self.cx, qpath, ptr.hir_id) {
574 if self.ptrs.contains(&id) {
577 NOT_UNSAFE_PTR_ARG_DEREF,
579 "this public function dereferences a raw pointer but is not marked `unsafe`",
587 struct StaticMutVisitor<'a, 'tcx> {
588 cx: &'a LateContext<'a, 'tcx>,
589 mutates_static: bool,
592 impl<'a, 'tcx> intravisit::Visitor<'tcx> for StaticMutVisitor<'a, 'tcx> {
593 type Map = Map<'tcx>;
595 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
596 use hir::ExprKind::{AddrOf, Assign, AssignOp, Call, MethodCall};
598 if self.mutates_static {
602 Call(_, args) | MethodCall(_, _, args) => {
603 let mut tys = FxHashSet::default();
605 let def_id = arg.hir_id.owner.to_def_id();
606 if self.cx.tcx.has_typeck_tables(def_id)
609 self.cx.tcx.typeck_tables_of(def_id).expr_ty(arg),
613 && is_mutated_static(self.cx, arg)
615 self.mutates_static = true;
621 Assign(ref target, ..) | AssignOp(_, ref target, _) | AddrOf(_, hir::Mutability::Mut, ref target) => {
622 self.mutates_static |= is_mutated_static(self.cx, target)
628 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
629 intravisit::NestedVisitorMap::None
633 fn is_mutated_static(cx: &LateContext<'_, '_>, e: &hir::Expr<'_>) -> bool {
634 use hir::ExprKind::{Field, Index, Path};
638 if let Res::Local(_) = qpath_res(cx, qpath, e.hir_id) {
644 Field(ref inner, _) | Index(ref inner, _) => is_mutated_static(cx, inner),
649 fn mutates_static<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, body: &'tcx hir::Body<'_>) -> bool {
650 let mut v = StaticMutVisitor {
652 mutates_static: false,
654 intravisit::walk_expr(&mut v, &body.value);