2 attrs::is_proc_macro, iter_input_pats, match_def_path, qpath_res, return_ty, snippet, snippet_opt,
3 span_help_and_lint, span_lint, span_lint_and_then, trait_ref_of_method, type_is_unsafe_function,
6 use rustc::hir::{self, def::Res, def_id::DefId, intravisit};
7 use rustc::impl_lint_pass;
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::ty::{self, Ty};
10 use rustc_data_structures::fx::FxHashSet;
11 use rustc_errors::Applicability;
12 use rustc_session::declare_tool_lint;
13 use rustc_target::spec::abi::Abi;
14 use syntax::ast::Attribute;
15 use syntax::source_map::Span;
17 declare_clippy_lint! {
18 /// **What it does:** Checks for functions with too many parameters.
20 /// **Why is this bad?** Functions with lots of parameters are considered bad
21 /// style and reduce readability (“what does the 5th parameter mean?”). Consider
22 /// grouping some parameters into a new type.
24 /// **Known problems:** None.
29 /// fn foo(x: u32, y: u32, name: &str, c: Color, w: f32, h: f32, a: f32, b: f32) {
33 pub TOO_MANY_ARGUMENTS,
35 "functions with too many arguments"
38 declare_clippy_lint! {
39 /// **What it does:** Checks for functions with a large amount of lines.
41 /// **Why is this bad?** Functions with a lot of lines are harder to understand
42 /// due to having to look at a larger amount of code to understand what the
43 /// function is doing. Consider splitting the body of the function into
44 /// multiple functions.
46 /// **Known problems:** None.
50 /// fn im_too_long() {
52 /// // ... 100 more LoC
58 "functions with too many lines"
61 declare_clippy_lint! {
62 /// **What it does:** Checks for public functions that dereference raw pointer
63 /// arguments but are not marked unsafe.
65 /// **Why is this bad?** The function should probably be marked `unsafe`, since
66 /// for an arbitrary raw pointer, there is no way of telling for sure if it is
69 /// **Known problems:**
71 /// * It does not check functions recursively so if the pointer is passed to a
72 /// private non-`unsafe` function which does the dereferencing, the lint won't
74 /// * It only checks for arguments whose type are raw pointers, not raw pointers
75 /// got from an argument in some other way (`fn foo(bar: &[*const u8])` or
76 /// `some_argument.get_raw_ptr()`).
80 /// pub fn foo(x: *const u8) {
81 /// println!("{}", unsafe { *x });
84 pub NOT_UNSAFE_PTR_ARG_DEREF,
86 "public functions dereferencing raw pointer arguments but not marked `unsafe`"
89 declare_clippy_lint! {
90 /// **What it does:** Checks for a [`#[must_use]`] attribute on
91 /// unit-returning functions and methods.
93 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
95 /// **Why is this bad?** Unit values are useless. The attribute is likely
96 /// a remnant of a refactoring that removed the return type.
98 /// **Known problems:** None.
107 "`#[must_use]` attribute on a unit-returning function / method"
110 declare_clippy_lint! {
111 /// **What it does:** Checks for a [`#[must_use]`] attribute without
112 /// further information on functions and methods that return a type already
113 /// marked as `#[must_use]`.
115 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
117 /// **Why is this bad?** The attribute isn't needed. Not using the result
118 /// will already be reported. Alternatively, one can add some text to the
119 /// attribute to improve the lint message.
121 /// **Known problems:** None.
126 /// fn double_must_use() -> Result<(), ()> {
127 /// unimplemented!();
132 "`#[must_use]` attribute on a `#[must_use]`-returning function / method"
135 declare_clippy_lint! {
136 /// **What it does:** Checks for public functions that have no
137 /// [`#[must_use]`] attribute, but return something not already marked
138 /// must-use, have no mutable arg and mutate no statics.
140 /// [`#[must_use]`]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute
142 /// **Why is this bad?** Not bad at all, this lint just shows places where
143 /// you could add the attribute.
145 /// **Known problems:** The lint only checks the arguments for mutable
146 /// types without looking if they are actually changed. On the other hand,
147 /// it also ignores a broad range of potentially interesting side effects,
148 /// because we cannot decide whether the programmer intends the function to
149 /// be called for the side effect or the result. Expect many false
150 /// positives. At least we don't lint if the result type is unit or already
155 /// // this could be annotated with `#[must_use]`.
156 /// fn id<T>(t: T) -> T { t }
158 pub MUST_USE_CANDIDATE,
160 "function or method that could take a `#[must_use]` attribute"
163 #[derive(Copy, Clone)]
164 pub struct Functions {
170 pub fn new(threshold: u64, max_lines: u64) -> Self {
171 Self { threshold, max_lines }
175 impl_lint_pass!(Functions => [
178 NOT_UNSAFE_PTR_ARG_DEREF,
184 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Functions {
187 cx: &LateContext<'a, 'tcx>,
188 kind: intravisit::FnKind<'tcx>,
189 decl: &'tcx hir::FnDecl,
190 body: &'tcx hir::Body,
194 let is_impl = if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
195 matches!(item.kind, hir::ItemKind::Impl(_, _, _, _, Some(_), _, _))
200 let unsafety = match kind {
201 hir::intravisit::FnKind::ItemFn(_, _, hir::FnHeader { unsafety, .. }, _, _) => unsafety,
202 hir::intravisit::FnKind::Method(_, sig, _, _) => sig.header.unsafety,
203 hir::intravisit::FnKind::Closure(_) => return,
206 // don't warn for implementations, it's not their fault
208 // don't lint extern functions decls, it's not their fault either
210 hir::intravisit::FnKind::Method(
213 header: hir::FnHeader { abi: Abi::Rust, .. },
219 | hir::intravisit::FnKind::ItemFn(_, _, hir::FnHeader { abi: Abi::Rust, .. }, _, _) => {
220 self.check_arg_number(cx, decl, span.with_hi(decl.output.span().hi()))
226 Self::check_raw_ptr(cx, unsafety, decl, body, hir_id);
227 self.check_line_number(cx, span, body);
230 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
231 let attr = must_use_attr(&item.attrs);
232 if let hir::ItemKind::Fn(ref sig, ref _generics, ref body_id) = item.kind {
233 if let Some(attr) = attr {
234 let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
235 check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr);
238 if cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(&item.attrs) {
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::Method(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::Method(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::TraitMethod::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 hir::intravisit::walk_expr(&mut v, expr);
402 fn check_needless_must_use(
403 cx: &LateContext<'_, '_>,
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",
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]`",
434 "either add some descriptive text or remove the attribute",
439 fn check_must_use_candidate<'a, 'tcx>(
440 cx: &LateContext<'a, 'tcx>,
441 decl: &'tcx hir::FnDecl,
442 body: &'tcx hir::Body,
448 if has_mutable_arg(cx, body)
449 || mutates_static(cx, body)
450 || in_external_macro(cx.sess(), item_span)
451 || returns_unit(decl)
452 || !cx.access_levels.is_exported(item_id)
453 || is_must_use_ty(cx, return_ty(cx, item_id))
457 span_lint_and_then(cx, MUST_USE_CANDIDATE, fn_span, msg, |db| {
458 if let Some(snippet) = snippet_opt(cx, fn_span) {
462 format!("#[must_use] {}", snippet),
463 Applicability::MachineApplicable,
469 fn must_use_attr(attrs: &[Attribute]) -> Option<&Attribute> {
470 attrs.iter().find(|attr| {
471 attr.ident().map_or(false, |ident| {
472 let ident: &str = &ident.as_str();
478 fn returns_unit(decl: &hir::FnDecl) -> bool {
480 hir::FunctionRetTy::DefaultReturn(_) => true,
481 hir::FunctionRetTy::Return(ref ty) => match ty.kind {
482 hir::TyKind::Tup(ref tys) => tys.is_empty(),
483 hir::TyKind::Never => true,
489 fn is_must_use_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>) -> bool {
492 Adt(ref adt, _) => must_use_attr(&cx.tcx.get_attrs(adt.did)).is_some(),
493 Foreign(ref did) => must_use_attr(&cx.tcx.get_attrs(*did)).is_some(),
494 Slice(ref ty) | Array(ref ty, _) | RawPtr(ty::TypeAndMut { ref ty, .. }) | Ref(_, ref ty, _) => {
495 // for the Array case we don't need to care for the len == 0 case
496 // because we don't want to lint functions returning empty arrays
497 is_must_use_ty(cx, *ty)
499 Tuple(ref substs) => substs.types().any(|ty| is_must_use_ty(cx, ty)),
500 Opaque(ref def_id, _) => {
501 for (predicate, _) in cx.tcx.predicates_of(*def_id).predicates {
502 if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
503 if must_use_attr(&cx.tcx.get_attrs(poly_trait_predicate.skip_binder().trait_ref.def_id)).is_some() {
510 Dynamic(binder, _) => {
511 for predicate in binder.skip_binder().iter() {
512 if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
513 if must_use_attr(&cx.tcx.get_attrs(trait_ref.def_id)).is_some() {
524 fn has_mutable_arg(cx: &LateContext<'_, '_>, body: &hir::Body) -> bool {
525 let mut tys = FxHashSet::default();
526 body.params.iter().any(|param| is_mutable_pat(cx, ¶m.pat, &mut tys))
529 fn is_mutable_pat(cx: &LateContext<'_, '_>, pat: &hir::Pat, tys: &mut FxHashSet<DefId>) -> bool {
530 if let hir::PatKind::Wild = pat.kind {
531 return false; // ignore `_` patterns
533 let def_id = pat.hir_id.owner_def_id();
534 if cx.tcx.has_typeck_tables(def_id) {
535 is_mutable_ty(cx, &cx.tcx.typeck_tables_of(def_id).pat_ty(pat), pat.span, tys)
541 static KNOWN_WRAPPER_TYS: &[&[&str]] = &[&["alloc", "rc", "Rc"], &["std", "sync", "Arc"]];
543 fn is_mutable_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>, span: Span, tys: &mut FxHashSet<DefId>) -> bool {
546 // primitive types are never mutable
547 Bool | Char | Int(_) | Uint(_) | Float(_) | Str => false,
548 Adt(ref adt, ref substs) => {
549 tys.insert(adt.did) && !ty.is_freeze(cx.tcx, cx.param_env, span)
550 || KNOWN_WRAPPER_TYS.iter().any(|path| match_def_path(cx, adt.did, path))
551 && substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys))
553 Tuple(ref substs) => substs.types().any(|ty| is_mutable_ty(cx, ty, span, tys)),
554 Array(ty, _) | Slice(ty) => is_mutable_ty(cx, ty, span, tys),
555 RawPtr(ty::TypeAndMut { ty, mutbl }) | Ref(_, ty, mutbl) => {
556 mutbl == hir::Mutability::Mut || is_mutable_ty(cx, ty, span, tys)
558 // calling something constitutes a side effect, so return true on all callables
559 // also never calls need not be used, so return true for them, too
564 fn raw_ptr_arg(arg: &hir::Param, ty: &hir::Ty) -> Option<hir::HirId> {
565 if let (&hir::PatKind::Binding(_, id, _, _), &hir::TyKind::Ptr(_)) = (&arg.pat.kind, &ty.kind) {
572 struct DerefVisitor<'a, 'tcx> {
573 cx: &'a LateContext<'a, 'tcx>,
574 ptrs: FxHashSet<hir::HirId>,
575 tables: &'a ty::TypeckTables<'tcx>,
578 impl<'a, 'tcx> intravisit::Visitor<'tcx> for DerefVisitor<'a, 'tcx> {
579 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
581 hir::ExprKind::Call(ref f, ref args) => {
582 let ty = self.tables.expr_ty(f);
584 if type_is_unsafe_function(self.cx, ty) {
590 hir::ExprKind::MethodCall(_, _, ref args) => {
591 let def_id = self.tables.type_dependent_def_id(expr.hir_id).unwrap();
592 let base_type = self.cx.tcx.type_of(def_id);
594 if type_is_unsafe_function(self.cx, base_type) {
600 hir::ExprKind::Unary(hir::UnDeref, ref ptr) => self.check_arg(ptr),
604 intravisit::walk_expr(self, expr);
607 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
608 intravisit::NestedVisitorMap::None
612 impl<'a, 'tcx> DerefVisitor<'a, 'tcx> {
613 fn check_arg(&self, ptr: &hir::Expr) {
614 if let hir::ExprKind::Path(ref qpath) = ptr.kind {
615 if let Res::Local(id) = qpath_res(self.cx, qpath, ptr.hir_id) {
616 if self.ptrs.contains(&id) {
619 NOT_UNSAFE_PTR_ARG_DEREF,
621 "this public function dereferences a raw pointer but is not marked `unsafe`",
629 struct StaticMutVisitor<'a, 'tcx> {
630 cx: &'a LateContext<'a, 'tcx>,
631 mutates_static: bool,
634 impl<'a, 'tcx> intravisit::Visitor<'tcx> for StaticMutVisitor<'a, 'tcx> {
635 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
636 use hir::ExprKind::*;
638 if self.mutates_static {
642 Call(_, ref args) | MethodCall(_, _, ref args) => {
643 let mut tys = FxHashSet::default();
645 let def_id = arg.hir_id.owner_def_id();
646 if self.cx.tcx.has_typeck_tables(def_id)
649 self.cx.tcx.typeck_tables_of(def_id).expr_ty(arg),
653 && is_mutated_static(self.cx, arg)
655 self.mutates_static = true;
661 Assign(ref target, _) | AssignOp(_, ref target, _) | AddrOf(_, hir::Mutability::Mut, ref target) => {
662 self.mutates_static |= is_mutated_static(self.cx, target)
668 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
669 intravisit::NestedVisitorMap::None
673 fn is_mutated_static(cx: &LateContext<'_, '_>, e: &hir::Expr) -> bool {
674 use hir::ExprKind::*;
678 if let Res::Local(_) = qpath_res(cx, qpath, e.hir_id) {
684 Field(ref inner, _) | Index(ref inner, _) => is_mutated_static(cx, inner),
689 fn mutates_static<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, body: &'tcx hir::Body) -> bool {
690 let mut v = StaticMutVisitor {
692 mutates_static: false,
694 intravisit::walk_expr(&mut v, &body.value);