1 use clippy_utils::diagnostics::{span_lint, span_lint_and_help, span_lint_and_then};
2 use clippy_utils::source::{snippet, snippet_opt};
3 use clippy_utils::ty::{is_must_use_ty, is_type_diagnostic_item, type_is_unsafe_function};
5 attr_by_name, attrs::is_proc_macro, is_trait_impl_item, iter_input_pats, match_def_path, must_use_attr,
6 path_to_local, return_ty, trait_ref_of_method,
8 use if_chain::if_chain;
9 use rustc_ast::ast::Attribute;
10 use rustc_data_structures::fx::FxHashSet;
11 use rustc_errors::Applicability;
13 use rustc_hir::intravisit;
14 use rustc_hir::{def::Res, def_id::DefId, QPath};
15 use rustc_lint::{LateContext, LateLintPass, LintContext};
16 use rustc_middle::hir::map::Map;
17 use rustc_middle::lint::in_external_macro;
18 use rustc_middle::ty::{self, Ty};
19 use rustc_session::{declare_tool_lint, impl_lint_pass};
20 use rustc_span::source_map::Span;
22 use rustc_target::spec::abi::Abi;
23 use rustc_typeck::hir_ty_to_ty;
25 declare_clippy_lint! {
26 /// **What it does:** Checks for functions with too many parameters.
28 /// **Why is this bad?** Functions with lots of parameters are considered bad
29 /// style and reduce readability (“what does the 5th parameter mean?”). Consider
30 /// grouping some parameters into a new type.
32 /// **Known problems:** None.
37 /// fn foo(x: u32, y: u32, name: &str, c: Color, w: f32, h: f32, a: f32, b: f32) {
41 pub TOO_MANY_ARGUMENTS,
43 "functions with too many arguments"
46 declare_clippy_lint! {
47 /// **What it does:** Checks for functions with a large amount of lines.
49 /// **Why is this bad?** Functions with a lot of lines are harder to understand
50 /// due to having to look at a larger amount of code to understand what the
51 /// function is doing. Consider splitting the body of the function into
52 /// multiple functions.
54 /// **Known problems:** None.
58 /// fn im_too_long() {
60 /// // ... 100 more LoC
66 "functions with too many lines"
69 declare_clippy_lint! {
70 /// **What it does:** Checks for public functions that dereference raw pointer
71 /// arguments but are not marked unsafe.
73 /// **Why is this bad?** The function should probably be marked `unsafe`, since
74 /// for an arbitrary raw pointer, there is no way of telling for sure if it is
77 /// **Known problems:**
79 /// * It does not check functions recursively so if the pointer is passed to a
80 /// private non-`unsafe` function which does the dereferencing, the lint won't
82 /// * It only checks for arguments whose type are raw pointers, not raw pointers
83 /// got from an argument in some other way (`fn foo(bar: &[*const u8])` or
84 /// `some_argument.get_raw_ptr()`).
89 /// pub fn foo(x: *const u8) {
90 /// println!("{}", unsafe { *x });
94 /// pub unsafe fn foo(x: *const u8) {
95 /// println!("{}", unsafe { *x });
98 pub NOT_UNSAFE_PTR_ARG_DEREF,
100 "public functions dereferencing raw pointer arguments but not marked `unsafe`"
103 declare_clippy_lint! {
104 /// **What it does:** Checks for a [`#[must_use]`] attribute on
105 /// unit-returning functions and methods.
107 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
109 /// **Why is this bad?** Unit values are useless. The attribute is likely
110 /// a remnant of a refactoring that removed the return type.
112 /// **Known problems:** None.
121 "`#[must_use]` attribute on a unit-returning function / method"
124 declare_clippy_lint! {
125 /// **What it does:** Checks for a [`#[must_use]`] attribute without
126 /// further information on functions and methods that return a type already
127 /// marked as `#[must_use]`.
129 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
131 /// **Why is this bad?** The attribute isn't needed. Not using the result
132 /// will already be reported. Alternatively, one can add some text to the
133 /// attribute to improve the lint message.
135 /// **Known problems:** None.
140 /// fn double_must_use() -> Result<(), ()> {
141 /// unimplemented!();
146 "`#[must_use]` attribute on a `#[must_use]`-returning function / method"
149 declare_clippy_lint! {
150 /// **What it does:** Checks for public functions that have no
151 /// [`#[must_use]`] attribute, but return something not already marked
152 /// must-use, have no mutable arg and mutate no statics.
154 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
156 /// **Why is this bad?** Not bad at all, this lint just shows places where
157 /// you could add the attribute.
159 /// **Known problems:** The lint only checks the arguments for mutable
160 /// types without looking if they are actually changed. On the other hand,
161 /// it also ignores a broad range of potentially interesting side effects,
162 /// because we cannot decide whether the programmer intends the function to
163 /// be called for the side effect or the result. Expect many false
164 /// positives. At least we don't lint if the result type is unit or already
169 /// // this could be annotated with `#[must_use]`.
170 /// fn id<T>(t: T) -> T { t }
172 pub MUST_USE_CANDIDATE,
174 "function or method that could take a `#[must_use]` attribute"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for public functions that return a `Result`
179 /// with an `Err` type of `()`. It suggests using a custom type that
180 /// implements [`std::error::Error`].
182 /// **Why is this bad?** Unit does not implement `Error` and carries no
183 /// further information about what went wrong.
185 /// **Known problems:** Of course, this lint assumes that `Result` is used
186 /// for a fallible operation (which is after all the intended use). However
187 /// code may opt to (mis)use it as a basic two-variant-enum. In that case,
188 /// the suggestion is misguided, and the code should use a custom enum
193 /// pub fn read_u8() -> Result<u8, ()> { Err(()) }
196 /// ```rust,should_panic
200 /// pub struct EndOfStream;
202 /// impl fmt::Display for EndOfStream {
203 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
204 /// write!(f, "End of Stream")
208 /// impl std::error::Error for EndOfStream { }
210 /// pub fn read_u8() -> Result<u8, EndOfStream> { Err(EndOfStream) }
212 ///# read_u8().unwrap();
216 /// Note that there are crates that simplify creating the error type, e.g.
217 /// [`thiserror`](https://docs.rs/thiserror).
220 "public function returning `Result` with an `Err` type of `()`"
223 #[derive(Copy, Clone)]
224 pub struct Functions {
230 pub fn new(threshold: u64, max_lines: u64) -> Self {
231 Self { threshold, max_lines }
235 impl_lint_pass!(Functions => [
238 NOT_UNSAFE_PTR_ARG_DEREF,
245 impl<'tcx> LateLintPass<'tcx> for Functions {
248 cx: &LateContext<'tcx>,
249 kind: intravisit::FnKind<'tcx>,
250 decl: &'tcx hir::FnDecl<'_>,
251 body: &'tcx hir::Body<'_>,
255 let unsafety = match kind {
256 intravisit::FnKind::ItemFn(_, _, hir::FnHeader { unsafety, .. }, _) => unsafety,
257 intravisit::FnKind::Method(_, sig, _) => sig.header.unsafety,
258 intravisit::FnKind::Closure => return,
261 // don't warn for implementations, it's not their fault
262 if !is_trait_impl_item(cx, hir_id) {
263 // don't lint extern functions decls, it's not their fault either
265 intravisit::FnKind::Method(
268 header: hir::FnHeader { abi: Abi::Rust, .. },
273 | intravisit::FnKind::ItemFn(_, _, hir::FnHeader { abi: Abi::Rust, .. }, _) => {
274 self.check_arg_number(cx, decl, span.with_hi(decl.output.span().hi()))
280 Self::check_raw_ptr(cx, unsafety, decl, body, hir_id);
281 self.check_line_number(cx, span, body);
284 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
285 let attrs = cx.tcx.hir().attrs(item.hir_id());
286 let attr = must_use_attr(attrs);
287 if let hir::ItemKind::Fn(ref sig, ref _generics, ref body_id) = item.kind {
288 let is_public = cx.access_levels.is_exported(item.hir_id());
289 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
291 check_result_unit_err(cx, &sig.decl, item.span, fn_header_span);
293 if let Some(attr) = attr {
294 check_needless_must_use(cx, &sig.decl, item.hir_id(), item.span, fn_header_span, attr);
297 if is_public && !is_proc_macro(cx.sess(), attrs) && attr_by_name(attrs, "no_mangle").is_none() {
298 check_must_use_candidate(
301 cx.tcx.hir().body(*body_id),
304 item.span.with_hi(sig.decl.output.span().hi()),
305 "this function could have a `#[must_use]` attribute",
311 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'_>) {
312 if let hir::ImplItemKind::Fn(ref sig, ref body_id) = item.kind {
313 let is_public = cx.access_levels.is_exported(item.hir_id());
314 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
315 if is_public && trait_ref_of_method(cx, item.hir_id()).is_none() {
316 check_result_unit_err(cx, &sig.decl, item.span, fn_header_span);
318 let attrs = cx.tcx.hir().attrs(item.hir_id());
319 let attr = must_use_attr(attrs);
320 if let Some(attr) = attr {
321 check_needless_must_use(cx, &sig.decl, item.hir_id(), item.span, fn_header_span, attr);
322 } else if is_public && !is_proc_macro(cx.sess(), attrs) && trait_ref_of_method(cx, item.hir_id()).is_none()
324 check_must_use_candidate(
327 cx.tcx.hir().body(*body_id),
330 item.span.with_hi(sig.decl.output.span().hi()),
331 "this method could have a `#[must_use]` attribute",
337 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'_>) {
338 if let hir::TraitItemKind::Fn(ref sig, ref eid) = item.kind {
339 // don't lint extern functions decls, it's not their fault
340 if sig.header.abi == Abi::Rust {
341 self.check_arg_number(cx, &sig.decl, item.span.with_hi(sig.decl.output.span().hi()));
343 let is_public = cx.access_levels.is_exported(item.hir_id());
344 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
346 check_result_unit_err(cx, &sig.decl, item.span, fn_header_span);
349 let attrs = cx.tcx.hir().attrs(item.hir_id());
350 let attr = must_use_attr(attrs);
351 if let Some(attr) = attr {
352 check_needless_must_use(cx, &sig.decl, item.hir_id(), item.span, fn_header_span, attr);
354 if let hir::TraitFn::Provided(eid) = *eid {
355 let body = cx.tcx.hir().body(eid);
356 Self::check_raw_ptr(cx, sig.header.unsafety, &sig.decl, body, item.hir_id());
358 if attr.is_none() && is_public && !is_proc_macro(cx.sess(), attrs) {
359 check_must_use_candidate(
365 item.span.with_hi(sig.decl.output.span().hi()),
366 "this method could have a `#[must_use]` attribute",
374 impl<'tcx> Functions {
375 fn check_arg_number(self, cx: &LateContext<'_>, decl: &hir::FnDecl<'_>, fn_span: Span) {
376 let args = decl.inputs.len() as u64;
377 if args > self.threshold {
382 &format!("this function has too many arguments ({}/{})", args, self.threshold),
387 fn check_line_number(self, cx: &LateContext<'_>, span: Span, body: &'tcx hir::Body<'_>) {
388 if in_external_macro(cx.sess(), span) {
392 let code_snippet = snippet(cx, body.value.span, "..");
393 let mut line_count: u64 = 0;
394 let mut in_comment = false;
395 let mut code_in_line;
397 // Skip the surrounding function decl.
398 let start_brace_idx = code_snippet.find('{').map_or(0, |i| i + 1);
399 let end_brace_idx = code_snippet.rfind('}').unwrap_or_else(|| code_snippet.len());
400 let function_lines = code_snippet[start_brace_idx..end_brace_idx].lines();
402 for mut line in function_lines {
403 code_in_line = false;
405 line = line.trim_start();
410 if let Some(i) = line.find("*/") {
411 line = &line[i + 2..];
416 let multi_idx = line.find("/*").unwrap_or_else(|| line.len());
417 let single_idx = line.find("//").unwrap_or_else(|| line.len());
418 code_in_line |= multi_idx > 0 && single_idx > 0;
419 // Implies multi_idx is below line.len()
420 if multi_idx < single_idx {
421 line = &line[multi_idx + 2..];
433 if line_count > self.max_lines {
438 &format!("this function has too many lines ({}/{})", line_count, self.max_lines),
444 cx: &LateContext<'tcx>,
445 unsafety: hir::Unsafety,
446 decl: &'tcx hir::FnDecl<'_>,
447 body: &'tcx hir::Body<'_>,
450 let expr = &body.value;
451 if unsafety == hir::Unsafety::Normal && cx.access_levels.is_exported(hir_id) {
452 let raw_ptrs = iter_input_pats(decl, body)
453 .zip(decl.inputs.iter())
454 .filter_map(|(arg, ty)| raw_ptr_arg(arg, ty))
455 .collect::<FxHashSet<_>>();
457 if !raw_ptrs.is_empty() {
458 let typeck_results = cx.tcx.typeck_body(body.id());
459 let mut v = DerefVisitor {
465 intravisit::walk_expr(&mut v, expr);
471 fn check_result_unit_err(cx: &LateContext<'_>, decl: &hir::FnDecl<'_>, item_span: Span, fn_header_span: Span) {
473 if !in_external_macro(cx.sess(), item_span);
474 if let hir::FnRetTy::Return(ref ty) = decl.output;
475 let ty = hir_ty_to_ty(cx.tcx, ty);
476 if is_type_diagnostic_item(cx, ty, sym::result_type);
477 if let ty::Adt(_, substs) = ty.kind();
478 let err_ty = substs.type_at(1);
485 "this returns a `Result<_, ()>",
487 "use a custom Error type instead",
493 fn check_needless_must_use(
494 cx: &LateContext<'_>,
495 decl: &hir::FnDecl<'_>,
498 fn_header_span: Span,
501 if in_external_macro(cx.sess(), item_span) {
504 if returns_unit(decl) {
509 "this unit-returning function has a `#[must_use]` attribute",
511 diag.span_suggestion(
513 "remove the attribute",
515 Applicability::MachineApplicable,
519 } else if !attr.is_value_str() && is_must_use_ty(cx, return_ty(cx, item_id)) {
524 "this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]`",
526 "either add some descriptive text or remove the attribute",
531 fn check_must_use_candidate<'tcx>(
532 cx: &LateContext<'tcx>,
533 decl: &'tcx hir::FnDecl<'_>,
534 body: &'tcx hir::Body<'_>,
540 if has_mutable_arg(cx, body)
541 || mutates_static(cx, body)
542 || in_external_macro(cx.sess(), item_span)
543 || returns_unit(decl)
544 || !cx.access_levels.is_exported(item_id)
545 || is_must_use_ty(cx, return_ty(cx, item_id))
549 span_lint_and_then(cx, MUST_USE_CANDIDATE, fn_span, msg, |diag| {
550 if let Some(snippet) = snippet_opt(cx, fn_span) {
551 diag.span_suggestion(
554 format!("#[must_use] {}", snippet),
555 Applicability::MachineApplicable,
561 fn returns_unit(decl: &hir::FnDecl<'_>) -> bool {
563 hir::FnRetTy::DefaultReturn(_) => true,
564 hir::FnRetTy::Return(ref ty) => match ty.kind {
565 hir::TyKind::Tup(ref tys) => tys.is_empty(),
566 hir::TyKind::Never => true,
572 fn has_mutable_arg(cx: &LateContext<'_>, body: &hir::Body<'_>) -> bool {
573 let mut tys = FxHashSet::default();
574 body.params.iter().any(|param| is_mutable_pat(cx, ¶m.pat, &mut tys))
577 fn is_mutable_pat(cx: &LateContext<'_>, pat: &hir::Pat<'_>, tys: &mut FxHashSet<DefId>) -> bool {
578 if let hir::PatKind::Wild = pat.kind {
579 return false; // ignore `_` patterns
581 if cx.tcx.has_typeck_results(pat.hir_id.owner.to_def_id()) {
582 is_mutable_ty(cx, &cx.tcx.typeck(pat.hir_id.owner).pat_ty(pat), pat.span, tys)
588 static KNOWN_WRAPPER_TYS: &[&[&str]] = &[&["alloc", "rc", "Rc"], &["std", "sync", "Arc"]];
590 fn is_mutable_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, span: Span, tys: &mut FxHashSet<DefId>) -> bool {
592 // primitive types are never mutable
593 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => false,
594 ty::Adt(ref adt, ref substs) => {
595 tys.insert(adt.did) && !ty.is_freeze(cx.tcx.at(span), cx.param_env)
596 || KNOWN_WRAPPER_TYS.iter().any(|path| match_def_path(cx, adt.did, path))
597 && substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys))
599 ty::Tuple(ref substs) => substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys)),
600 ty::Array(ty, _) | ty::Slice(ty) => is_mutable_ty(cx, ty, span, tys),
601 ty::RawPtr(ty::TypeAndMut { ty, mutbl }) | ty::Ref(_, ty, mutbl) => {
602 mutbl == hir::Mutability::Mut || is_mutable_ty(cx, ty, span, tys)
604 // calling something constitutes a side effect, so return true on all callables
605 // also never calls need not be used, so return true for them, too
610 fn raw_ptr_arg(arg: &hir::Param<'_>, ty: &hir::Ty<'_>) -> Option<hir::HirId> {
611 if let (&hir::PatKind::Binding(_, id, _, _), &hir::TyKind::Ptr(_)) = (&arg.pat.kind, &ty.kind) {
618 struct DerefVisitor<'a, 'tcx> {
619 cx: &'a LateContext<'tcx>,
620 ptrs: FxHashSet<hir::HirId>,
621 typeck_results: &'a ty::TypeckResults<'tcx>,
624 impl<'a, 'tcx> intravisit::Visitor<'tcx> for DerefVisitor<'a, 'tcx> {
625 type Map = Map<'tcx>;
627 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
629 hir::ExprKind::Call(ref f, args) => {
630 let ty = self.typeck_results.expr_ty(f);
632 if type_is_unsafe_function(self.cx, ty) {
638 hir::ExprKind::MethodCall(_, _, args, _) => {
639 let def_id = self.typeck_results.type_dependent_def_id(expr.hir_id).unwrap();
640 let base_type = self.cx.tcx.type_of(def_id);
642 if type_is_unsafe_function(self.cx, base_type) {
648 hir::ExprKind::Unary(hir::UnOp::Deref, ref ptr) => self.check_arg(ptr),
652 intravisit::walk_expr(self, expr);
655 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
656 intravisit::NestedVisitorMap::None
660 impl<'a, 'tcx> DerefVisitor<'a, 'tcx> {
661 fn check_arg(&self, ptr: &hir::Expr<'_>) {
662 if let Some(id) = path_to_local(ptr) {
663 if self.ptrs.contains(&id) {
666 NOT_UNSAFE_PTR_ARG_DEREF,
668 "this public function dereferences a raw pointer but is not marked `unsafe`",
675 struct StaticMutVisitor<'a, 'tcx> {
676 cx: &'a LateContext<'tcx>,
677 mutates_static: bool,
680 impl<'a, 'tcx> intravisit::Visitor<'tcx> for StaticMutVisitor<'a, 'tcx> {
681 type Map = Map<'tcx>;
683 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
684 use hir::ExprKind::{AddrOf, Assign, AssignOp, Call, MethodCall};
686 if self.mutates_static {
690 Call(_, args) | MethodCall(_, _, args, _) => {
691 let mut tys = FxHashSet::default();
693 if self.cx.tcx.has_typeck_results(arg.hir_id.owner.to_def_id())
696 self.cx.tcx.typeck(arg.hir_id.owner).expr_ty(arg),
700 && is_mutated_static(arg)
702 self.mutates_static = true;
708 Assign(ref target, ..) | AssignOp(_, ref target, _) | AddrOf(_, hir::Mutability::Mut, ref target) => {
709 self.mutates_static |= is_mutated_static(target)
715 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
716 intravisit::NestedVisitorMap::None
720 fn is_mutated_static(e: &hir::Expr<'_>) -> bool {
721 use hir::ExprKind::{Field, Index, Path};
724 Path(QPath::Resolved(_, path)) => !matches!(path.res, Res::Local(_)),
726 Field(ref inner, _) | Index(ref inner, _) => is_mutated_static(inner),
731 fn mutates_static<'tcx>(cx: &LateContext<'tcx>, body: &'tcx hir::Body<'_>) -> bool {
732 let mut v = StaticMutVisitor {
734 mutates_static: false,
736 intravisit::walk_expr(&mut v, &body.value);