6 mod redundant_allocation;
12 use rustc_hir::intravisit::FnKind;
14 Body, FnDecl, FnRetTy, GenericArg, HirId, ImplItem, ImplItemKind, Item, ItemKind, Local, MutTy, QPath, TraitItem,
15 TraitItemKind, TyKind,
17 use rustc_lint::{LateContext, LateLintPass};
18 use rustc_session::{declare_tool_lint, impl_lint_pass};
19 use rustc_span::source_map::Span;
21 declare_clippy_lint! {
22 /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
23 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
25 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
26 /// the heap. So if you `Box` it, you just add another level of indirection
27 /// without any benefit whatsoever.
29 /// **Known problems:** None.
34 /// values: Box<Vec<Foo>>,
47 "usage of `Box<Vec<T>>`, vector elements are already on the heap"
50 declare_clippy_lint! {
51 /// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
52 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
54 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
55 /// the heap. So if you `Box` its contents, you just add another level of indirection.
57 /// **Known problems:** Vec<Box<T: Sized>> makes sense if T is a large type (see [#3530](https://github.com/rust-lang/rust-clippy/issues/3530),
63 /// values: Vec<Box<i32>>,
76 "usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
79 declare_clippy_lint! {
80 /// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
83 /// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
84 /// represents an optional optional value which is logically the same thing as an optional
85 /// value but has an unneeded extra level of wrapping.
87 /// If you have a case where `Some(Some(_))`, `Some(None)` and `None` are distinct cases,
88 /// consider a custom `enum` instead, with clear names for each case.
90 /// **Known problems:** None.
94 /// fn get_data() -> Option<Option<u32>> {
102 /// pub enum Contents {
103 /// Data(Vec<u8>), // Was Some(Some(Vec<u8>))
104 /// NotYetFetched, // Was Some(None)
105 /// None, // Was None
108 /// fn get_data() -> Contents {
114 "usage of `Option<Option<T>>`"
117 declare_clippy_lint! {
118 /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
119 /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
121 /// **Why is this bad?** Gankro says:
123 /// > The TL;DR of `LinkedList` is that it's built on a massive amount of
124 /// pointers and indirection.
125 /// > It wastes memory, it has terrible cache locality, and is all-around slow.
127 /// > "only" amortized for push/pop, should be faster in the general case for
128 /// almost every possible
129 /// > workload, and isn't even amortized at all if you can predict the capacity
132 /// > `LinkedList`s are only really good if you're doing a lot of merging or
133 /// splitting of lists.
134 /// > This is because they can just mangle some pointers instead of actually
135 /// copying the data. Even
136 /// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
137 /// can still be better
138 /// > because of how expensive it is to seek to the middle of a `LinkedList`.
140 /// **Known problems:** False positives – the instances where using a
141 /// `LinkedList` makes sense are few and far between, but they can still happen.
145 /// # use std::collections::LinkedList;
146 /// let x: LinkedList<usize> = LinkedList::new();
150 "usage of LinkedList, usually a vector is faster, or a more specialized data structure like a `VecDeque`"
153 declare_clippy_lint! {
154 /// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
155 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
157 /// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
160 /// **Known problems:** None.
164 /// fn foo(bar: &Box<T>) { ... }
170 /// fn foo(bar: &T) { ... }
174 "a borrow of a boxed type"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for use of redundant allocations anywhere in the code.
180 /// **Why is this bad?** Expressions such as `Rc<&T>`, `Rc<Rc<T>>`, `Rc<Box<T>>`, `Box<&T>`
181 /// add an unnecessary level of indirection.
183 /// **Known problems:** None.
187 /// # use std::rc::Rc;
188 /// fn foo(bar: Rc<&usize>) {}
194 /// fn foo(bar: &usize) {}
196 pub REDUNDANT_ALLOCATION,
198 "redundant allocation"
201 declare_clippy_lint! {
202 /// **What it does:** Checks for `Rc<T>` and `Arc<T>` when `T` is a mutable buffer type such as `String` or `Vec`.
204 /// **Why is this bad?** Expressions such as `Rc<String>` usually have no advantage over `Rc<str>`, since
205 /// it is larger and involves an extra level of indirection, and doesn't implement `Borrow<str>`.
207 /// While mutating a buffer type would still be possible with `Rc::get_mut()`, it only
208 /// works if there are no additional references yet, which usually defeats the purpose of
209 /// enclosing it in a shared ownership type. Instead, additionally wrapping the inner
210 /// type with an interior mutable container (such as `RefCell` or `Mutex`) would normally
213 /// **Known problems:** This pattern can be desirable to avoid the overhead of a `RefCell` or `Mutex` for
214 /// cases where mutation only happens before there are any additional references.
218 /// # use std::rc::Rc;
219 /// fn foo(interned: Rc<String>) { ... }
225 /// fn foo(interned: Rc<str>) { ... }
229 "shared ownership of a buffer type"
232 declare_clippy_lint! {
233 /// **What it does:** Checks for types used in structs, parameters and `let`
234 /// declarations above a certain complexity threshold.
236 /// **Why is this bad?** Too complex types make the code less readable. Consider
237 /// using a `type` definition to simplify them.
239 /// **Known problems:** None.
243 /// # use std::rc::Rc;
245 /// inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
250 "usage of very complex types that might be better factored into `type` definitions"
254 vec_box_size_threshold: u64,
255 type_complexity_threshold: u64,
258 impl_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX, REDUNDANT_ALLOCATION, RC_BUFFER, TYPE_COMPLEXITY]);
260 impl<'tcx> LateLintPass<'tcx> for Types {
261 fn check_fn(&mut self, cx: &LateContext<'_>, _: FnKind<'_>, decl: &FnDecl<'_>, _: &Body<'_>, _: Span, id: HirId) {
262 let is_in_trait_impl = if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id))
264 matches!(item.kind, ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }))
274 ..CheckTyContext::default()
279 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
281 ItemKind::Static(ty, _, _) | ItemKind::Const(ty, _) => self.check_ty(cx, ty, CheckTyContext::default()),
282 // functions, enums, structs, impls and traits are covered
287 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
289 ImplItemKind::Const(ty, _) | ImplItemKind::TyAlias(ty) => self.check_ty(
293 is_in_trait_impl: true,
294 ..CheckTyContext::default()
297 // methods are covered by check_fn
298 ImplItemKind::Fn(..) => (),
302 fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
303 self.check_ty(cx, field.ty, CheckTyContext::default());
306 fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &TraitItem<'_>) {
308 TraitItemKind::Const(ty, _) | TraitItemKind::Type(_, Some(ty)) => {
309 self.check_ty(cx, ty, CheckTyContext::default());
311 TraitItemKind::Fn(ref sig, _) => self.check_fn_decl(cx, sig.decl, CheckTyContext::default()),
312 TraitItemKind::Type(..) => (),
316 fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
317 if let Some(ty) = local.ty {
323 ..CheckTyContext::default()
331 pub fn new(vec_box_size_threshold: u64, type_complexity_threshold: u64) -> Self {
333 vec_box_size_threshold,
334 type_complexity_threshold,
338 fn check_fn_decl(&mut self, cx: &LateContext<'_>, decl: &FnDecl<'_>, context: CheckTyContext) {
339 for input in decl.inputs {
340 self.check_ty(cx, input, context);
343 if let FnRetTy::Return(ty) = decl.output {
344 self.check_ty(cx, ty, context);
348 /// Recursively check for `TypePass` lints in the given type. Stop at the first
351 /// The parameter `is_local` distinguishes the context of the type.
352 fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, mut context: CheckTyContext) {
353 if hir_ty.span.from_expansion() {
357 if !context.is_nested_call && type_complexity::check(cx, hir_ty, self.type_complexity_threshold) {
361 // Skip trait implementations; see issue #605.
362 if context.is_in_trait_impl {
367 TyKind::Path(ref qpath) if !context.is_local => {
368 let hir_id = hir_ty.hir_id;
369 let res = cx.qpath_res(qpath, hir_id);
370 if let Some(def_id) = res.opt_def_id() {
371 let mut triggered = false;
372 triggered |= box_vec::check(cx, hir_ty, qpath, def_id);
373 triggered |= redundant_allocation::check(cx, hir_ty, qpath, def_id);
374 triggered |= rc_buffer::check(cx, hir_ty, qpath, def_id);
375 triggered |= vec_box::check(cx, hir_ty, qpath, def_id, self.vec_box_size_threshold);
376 triggered |= option_option::check(cx, hir_ty, qpath, def_id);
377 triggered |= linked_list::check(cx, hir_ty, def_id);
384 QPath::Resolved(Some(ty), p) => {
385 context.is_nested_call = true;
386 self.check_ty(cx, ty, context);
387 for ty in p.segments.iter().flat_map(|seg| {
390 .map_or_else(|| [].iter(), |params| params.args.iter())
391 .filter_map(|arg| match arg {
392 GenericArg::Type(ty) => Some(ty),
396 self.check_ty(cx, ty, context);
399 QPath::Resolved(None, p) => {
400 context.is_nested_call = true;
401 for ty in p.segments.iter().flat_map(|seg| {
404 .map_or_else(|| [].iter(), |params| params.args.iter())
405 .filter_map(|arg| match arg {
406 GenericArg::Type(ty) => Some(ty),
410 self.check_ty(cx, ty, context);
413 QPath::TypeRelative(ty, seg) => {
414 context.is_nested_call = true;
415 self.check_ty(cx, ty, context);
416 if let Some(params) = seg.args {
417 for ty in params.args.iter().filter_map(|arg| match arg {
418 GenericArg::Type(ty) => Some(ty),
421 self.check_ty(cx, ty, context);
425 QPath::LangItem(..) => {},
428 TyKind::Rptr(ref lt, ref mut_ty) => {
429 context.is_nested_call = true;
430 if !borrowed_box::check(cx, hir_ty, lt, mut_ty) {
431 self.check_ty(cx, mut_ty.ty, context);
434 TyKind::Slice(ty) | TyKind::Array(ty, _) | TyKind::Ptr(MutTy { ty, .. }) => {
435 context.is_nested_call = true;
436 self.check_ty(cx, ty, context);
438 TyKind::Tup(tys) => {
439 context.is_nested_call = true;
441 self.check_ty(cx, ty, context);
449 #[derive(Clone, Copy, Default)]
450 struct CheckTyContext {
451 is_in_trait_impl: bool,
453 is_nested_call: bool,