7 mod redundant_allocation;
13 use rustc_hir::intravisit::FnKind;
15 Body, FnDecl, FnRetTy, GenericArg, HirId, ImplItem, ImplItemKind, Item, ItemKind, Local, MutTy, QPath, TraitItem,
16 TraitItemKind, TyKind,
18 use rustc_lint::{LateContext, LateLintPass};
19 use rustc_session::{declare_tool_lint, impl_lint_pass};
20 use rustc_span::source_map::Span;
22 declare_clippy_lint! {
23 /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
24 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
26 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
27 /// the heap. So if you `Box` it, you just add another level of indirection
28 /// without any benefit whatsoever.
30 /// **Known problems:** None.
35 /// values: Box<Vec<Foo>>,
48 "usage of `Box<Vec<T>>`, vector elements are already on the heap"
51 declare_clippy_lint! {
52 /// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
53 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
55 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
56 /// the heap. So if you `Box` its contents, you just add another level of indirection.
58 /// **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),
64 /// values: Vec<Box<i32>>,
77 "usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
80 declare_clippy_lint! {
81 /// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
84 /// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
85 /// represents an optional optional value which is logically the same thing as an optional
86 /// value but has an unneeded extra level of wrapping.
88 /// If you have a case where `Some(Some(_))`, `Some(None)` and `None` are distinct cases,
89 /// consider a custom `enum` instead, with clear names for each case.
91 /// **Known problems:** None.
95 /// fn get_data() -> Option<Option<u32>> {
103 /// pub enum Contents {
104 /// Data(Vec<u8>), // Was Some(Some(Vec<u8>))
105 /// NotYetFetched, // Was Some(None)
106 /// None, // Was None
109 /// fn get_data() -> Contents {
115 "usage of `Option<Option<T>>`"
118 declare_clippy_lint! {
119 /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
120 /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
122 /// **Why is this bad?** Gankro says:
124 /// > The TL;DR of `LinkedList` is that it's built on a massive amount of
125 /// pointers and indirection.
126 /// > It wastes memory, it has terrible cache locality, and is all-around slow.
128 /// > "only" amortized for push/pop, should be faster in the general case for
129 /// almost every possible
130 /// > workload, and isn't even amortized at all if you can predict the capacity
133 /// > `LinkedList`s are only really good if you're doing a lot of merging or
134 /// splitting of lists.
135 /// > This is because they can just mangle some pointers instead of actually
136 /// copying the data. Even
137 /// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
138 /// can still be better
139 /// > because of how expensive it is to seek to the middle of a `LinkedList`.
141 /// **Known problems:** False positives – the instances where using a
142 /// `LinkedList` makes sense are few and far between, but they can still happen.
146 /// # use std::collections::LinkedList;
147 /// let x: LinkedList<usize> = LinkedList::new();
151 "usage of LinkedList, usually a vector is faster, or a more specialized data structure like a `VecDeque`"
154 declare_clippy_lint! {
155 /// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
156 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
158 /// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
161 /// **Known problems:** None.
165 /// fn foo(bar: &Box<T>) { ... }
171 /// fn foo(bar: &T) { ... }
175 "a borrow of a boxed type"
178 declare_clippy_lint! {
179 /// **What it does:** Checks for use of redundant allocations anywhere in the code.
181 /// **Why is this bad?** Expressions such as `Rc<&T>`, `Rc<Rc<T>>`, `Rc<Box<T>>`, `Box<&T>`
182 /// add an unnecessary level of indirection.
184 /// **Known problems:** None.
188 /// # use std::rc::Rc;
189 /// fn foo(bar: Rc<&usize>) {}
195 /// fn foo(bar: &usize) {}
197 pub REDUNDANT_ALLOCATION,
199 "redundant allocation"
202 declare_clippy_lint! {
203 /// **What it does:** Checks for `Rc<T>` and `Arc<T>` when `T` is a mutable buffer type such as `String` or `Vec`.
205 /// **Why is this bad?** Expressions such as `Rc<String>` usually have no advantage over `Rc<str>`, since
206 /// it is larger and involves an extra level of indirection, and doesn't implement `Borrow<str>`.
208 /// While mutating a buffer type would still be possible with `Rc::get_mut()`, it only
209 /// works if there are no additional references yet, which usually defeats the purpose of
210 /// enclosing it in a shared ownership type. Instead, additionally wrapping the inner
211 /// type with an interior mutable container (such as `RefCell` or `Mutex`) would normally
214 /// **Known problems:** This pattern can be desirable to avoid the overhead of a `RefCell` or `Mutex` for
215 /// cases where mutation only happens before there are any additional references.
219 /// # use std::rc::Rc;
220 /// fn foo(interned: Rc<String>) { ... }
226 /// fn foo(interned: Rc<str>) { ... }
230 "shared ownership of a buffer type"
233 declare_clippy_lint! {
234 /// **What it does:** Checks for types used in structs, parameters and `let`
235 /// declarations above a certain complexity threshold.
237 /// **Why is this bad?** Too complex types make the code less readable. Consider
238 /// using a `type` definition to simplify them.
240 /// **Known problems:** None.
244 /// # use std::rc::Rc;
246 /// inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
251 "usage of very complex types that might be better factored into `type` definitions"
254 declare_clippy_lint! {
255 /// **What it does:** Checks for `Rc<Mutex<T>>`.
257 /// **Why is this bad?** `Rc<Mutex<T>>` may introduce a deadlock in single thread. Consider
258 /// using `Rc<RefCell<T>>` instead.
262 /// use std::sync::Mutex;
264 /// let a: Rc<Mutex<i32>> = Rc::new(Mutex::new(1));
265 /// let a_clone = a.clone();
266 /// let mut data = a.lock().unwrap();
267 /// println!("{:?}", *a_clone.lock().unwrap());
272 /// **Known problems:** `Rc<RefCell<T>>` may panic in runtime.
277 /// use std::sync::Mutex;
278 /// fn foo(interned: Rc<Mutex<i32>>) { ... }
285 /// use std::cell::RefCell
286 /// fn foo(interned: Rc<RefCell<i32>>) { ... }
290 "usage of `Rc<Mutex<T>>`"
294 vec_box_size_threshold: u64,
295 type_complexity_threshold: u64,
298 impl_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX, REDUNDANT_ALLOCATION, RC_BUFFER, RC_MUTEX, TYPE_COMPLEXITY]);
300 impl<'tcx> LateLintPass<'tcx> for Types {
301 fn check_fn(&mut self, cx: &LateContext<'_>, _: FnKind<'_>, decl: &FnDecl<'_>, _: &Body<'_>, _: Span, id: HirId) {
302 let is_in_trait_impl = if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id))
304 matches!(item.kind, ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }))
314 ..CheckTyContext::default()
319 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
321 ItemKind::Static(ty, _, _) | ItemKind::Const(ty, _) => self.check_ty(cx, ty, CheckTyContext::default()),
322 // functions, enums, structs, impls and traits are covered
327 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
329 ImplItemKind::Const(ty, _) | ImplItemKind::TyAlias(ty) => self.check_ty(
333 is_in_trait_impl: true,
334 ..CheckTyContext::default()
337 // methods are covered by check_fn
338 ImplItemKind::Fn(..) => (),
342 fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
343 self.check_ty(cx, field.ty, CheckTyContext::default());
346 fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &TraitItem<'_>) {
348 TraitItemKind::Const(ty, _) | TraitItemKind::Type(_, Some(ty)) => {
349 self.check_ty(cx, ty, CheckTyContext::default());
351 TraitItemKind::Fn(ref sig, _) => self.check_fn_decl(cx, sig.decl, CheckTyContext::default()),
352 TraitItemKind::Type(..) => (),
356 fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
357 if let Some(ty) = local.ty {
363 ..CheckTyContext::default()
371 pub fn new(vec_box_size_threshold: u64, type_complexity_threshold: u64) -> Self {
373 vec_box_size_threshold,
374 type_complexity_threshold,
378 fn check_fn_decl(&mut self, cx: &LateContext<'_>, decl: &FnDecl<'_>, context: CheckTyContext) {
379 for input in decl.inputs {
380 self.check_ty(cx, input, context);
383 if let FnRetTy::Return(ty) = decl.output {
384 self.check_ty(cx, ty, context);
388 /// Recursively check for `TypePass` lints in the given type. Stop at the first
391 /// The parameter `is_local` distinguishes the context of the type.
392 fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, mut context: CheckTyContext) {
393 if hir_ty.span.from_expansion() {
397 if !context.is_nested_call && type_complexity::check(cx, hir_ty, self.type_complexity_threshold) {
401 // Skip trait implementations; see issue #605.
402 if context.is_in_trait_impl {
407 TyKind::Path(ref qpath) if !context.is_local => {
408 let hir_id = hir_ty.hir_id;
409 let res = cx.qpath_res(qpath, hir_id);
410 if let Some(def_id) = res.opt_def_id() {
411 let mut triggered = false;
412 triggered |= box_vec::check(cx, hir_ty, qpath, def_id);
413 triggered |= redundant_allocation::check(cx, hir_ty, qpath, def_id);
414 triggered |= rc_buffer::check(cx, hir_ty, qpath, def_id);
415 triggered |= vec_box::check(cx, hir_ty, qpath, def_id, self.vec_box_size_threshold);
416 triggered |= option_option::check(cx, hir_ty, qpath, def_id);
417 triggered |= linked_list::check(cx, hir_ty, def_id);
418 triggered |= rc_mutex::check(cx, hir_ty, qpath, def_id);
425 QPath::Resolved(Some(ty), p) => {
426 context.is_nested_call = true;
427 self.check_ty(cx, ty, context);
428 for ty in p.segments.iter().flat_map(|seg| {
431 .map_or_else(|| [].iter(), |params| params.args.iter())
432 .filter_map(|arg| match arg {
433 GenericArg::Type(ty) => Some(ty),
437 self.check_ty(cx, ty, context);
440 QPath::Resolved(None, p) => {
441 context.is_nested_call = true;
442 for ty in p.segments.iter().flat_map(|seg| {
445 .map_or_else(|| [].iter(), |params| params.args.iter())
446 .filter_map(|arg| match arg {
447 GenericArg::Type(ty) => Some(ty),
451 self.check_ty(cx, ty, context);
454 QPath::TypeRelative(ty, seg) => {
455 context.is_nested_call = true;
456 self.check_ty(cx, ty, context);
457 if let Some(params) = seg.args {
458 for ty in params.args.iter().filter_map(|arg| match arg {
459 GenericArg::Type(ty) => Some(ty),
462 self.check_ty(cx, ty, context);
466 QPath::LangItem(..) => {},
469 TyKind::Rptr(ref lt, ref mut_ty) => {
470 context.is_nested_call = true;
471 if !borrowed_box::check(cx, hir_ty, lt, mut_ty) {
472 self.check_ty(cx, mut_ty.ty, context);
475 TyKind::Slice(ty) | TyKind::Array(ty, _) | TyKind::Ptr(MutTy { ty, .. }) => {
476 context.is_nested_call = true;
477 self.check_ty(cx, ty, context);
479 TyKind::Tup(tys) => {
480 context.is_nested_call = true;
482 self.check_ty(cx, ty, context);
490 #[derive(Clone, Copy, Default)]
491 struct CheckTyContext {
492 is_in_trait_impl: bool,
494 is_nested_call: bool,