1 //! Checks for usage of `&Vec[_]` and `&String`.
3 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then};
4 use clippy_utils::ptr::get_spans;
5 use clippy_utils::source::snippet_opt;
6 use clippy_utils::ty::walk_ptrs_hir_ty;
7 use clippy_utils::{expr_path_res, is_lint_allowed, match_any_diagnostic_items, paths};
8 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::def::Res;
12 BinOpKind, BodyId, Expr, ExprKind, FnDecl, FnRetTy, GenericArg, Impl, ImplItem, ImplItemKind, Item, ItemKind,
13 Lifetime, MutTy, Mutability, Node, PathSegment, QPath, TraitFn, TraitItem, TraitItemKind, Ty, TyKind,
15 use rustc_lint::{LateContext, LateLintPass};
16 use rustc_session::{declare_lint_pass, declare_tool_lint};
17 use rustc_span::source_map::Span;
18 use rustc_span::symbol::Symbol;
19 use rustc_span::{sym, MultiSpan};
22 declare_clippy_lint! {
24 /// This lint checks for function arguments of type `&String`
25 /// or `&Vec` unless the references are mutable. It will also suggest you
26 /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
29 /// ### Why is this bad?
30 /// Requiring the argument to be of the specific size
31 /// makes the function less useful for no benefit; slices in the form of `&[T]`
32 /// or `&str` usually suffice and can be obtained from other types, too.
34 /// ### Known problems
35 /// The lint does not follow data. So if you have an
36 /// argument `x` and write `let y = x; y.clone()` the lint will not suggest
37 /// changing that `.clone()` to `.to_owned()`.
39 /// Other functions called from this function taking a `&String` or `&Vec`
40 /// argument may also fail to compile if you change the argument. Applying
41 /// this lint on them will fix the problem, but they may be in other crates.
43 /// One notable example of a function that may cause issues, and which cannot
44 /// easily be changed due to being in the standard library is `Vec::contains`.
45 /// when called on a `Vec<Vec<T>>`. If a `&Vec` is passed to that method then
46 /// it will compile, but if a `&[T]` is passed then it will not compile.
49 /// fn cannot_take_a_slice(v: &Vec<u8>) -> bool {
50 /// let vec_of_vecs: Vec<Vec<u8>> = some_other_fn();
52 /// vec_of_vecs.contains(v)
56 /// Also there may be `fn(&Vec)`-typed references pointing to your function.
57 /// If you have them, you will get a compiler error after applying this lint's
58 /// suggestions. You then have the choice to undo your changes or change the
59 /// type of the reference.
61 /// Note that if the function is part of your public interface, there may be
62 /// other crates referencing it, of which you may not be aware. Carefully
63 /// deprecate the function before applying the lint suggestions in this case.
68 /// fn foo(&Vec<u32>) { .. }
71 /// fn foo(&[u32]) { .. }
73 #[clippy::version = "pre 1.29.0"]
76 "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
79 declare_clippy_lint! {
81 /// This lint checks for equality comparisons with `ptr::null`
83 /// ### Why is this bad?
84 /// It's easier and more readable to use the inherent
91 /// if x == ptr::null {
100 #[clippy::version = "pre 1.29.0"]
103 "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead"
106 declare_clippy_lint! {
108 /// This lint checks for functions that take immutable
109 /// references and return mutable ones.
111 /// ### Why is this bad?
112 /// This is trivially unsound, as one can create two
113 /// mutable references from the same (immutable!) source.
114 /// This [error](https://github.com/rust-lang/rust/issues/39465)
115 /// actually lead to an interim Rust release 1.15.1.
117 /// ### Known problems
118 /// To be on the conservative side, if there's at least one
119 /// mutable reference with the output lifetime, this lint will not trigger.
120 /// In practice, this case is unlikely anyway.
124 /// fn foo(&Foo) -> &mut Bar { .. }
126 #[clippy::version = "pre 1.29.0"]
129 "fns that create mutable refs from immutable ref args"
132 declare_clippy_lint! {
134 /// This lint checks for invalid usages of `ptr::null`.
136 /// ### Why is this bad?
137 /// This causes undefined behavior.
141 /// // Bad. Undefined behavior
142 /// unsafe { std::slice::from_raw_parts(ptr::null(), 0); }
147 /// unsafe { std::slice::from_raw_parts(NonNull::dangling().as_ptr(), 0); }
149 #[clippy::version = "1.53.0"]
150 pub INVALID_NULL_PTR_USAGE,
152 "invalid usage of a null pointer, suggesting `NonNull::dangling()` instead"
155 declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF, INVALID_NULL_PTR_USAGE]);
157 impl<'tcx> LateLintPass<'tcx> for Ptr {
158 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
159 if let ItemKind::Fn(ref sig, _, body_id) = item.kind {
160 check_fn(cx, sig.decl, Some(body_id));
164 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
165 if let ImplItemKind::Fn(ref sig, body_id) = item.kind {
166 let parent_item = cx.tcx.hir().get_parent_item(item.hir_id());
167 if let Some(Node::Item(it)) = cx.tcx.hir().find(parent_item) {
168 if let ItemKind::Impl(Impl { of_trait: Some(_), .. }) = it.kind {
169 return; // ignore trait impls
172 check_fn(cx, sig.decl, Some(body_id));
176 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
177 if let TraitItemKind::Fn(ref sig, ref trait_method) = item.kind {
178 let body_id = if let TraitFn::Provided(b) = *trait_method {
183 check_fn(cx, sig.decl, body_id);
187 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
188 if let ExprKind::Binary(ref op, l, r) = expr.kind {
189 if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(cx, l) || is_null_path(cx, r)) {
194 "comparing with null is better expressed by the `.is_null()` method",
198 check_invalid_ptr_usage(cx, expr);
203 fn check_invalid_ptr_usage<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
204 // (fn_path, arg_indices) - `arg_indices` are the `arg` positions where null would cause U.B.
205 const INVALID_NULL_PTR_USAGE_TABLE: [(&[&str], &[usize]); 16] = [
206 (&paths::SLICE_FROM_RAW_PARTS, &[0]),
207 (&paths::SLICE_FROM_RAW_PARTS_MUT, &[0]),
208 (&paths::PTR_COPY, &[0, 1]),
209 (&paths::PTR_COPY_NONOVERLAPPING, &[0, 1]),
210 (&paths::PTR_READ, &[0]),
211 (&paths::PTR_READ_UNALIGNED, &[0]),
212 (&paths::PTR_READ_VOLATILE, &[0]),
213 (&paths::PTR_REPLACE, &[0]),
214 (&paths::PTR_SLICE_FROM_RAW_PARTS, &[0]),
215 (&paths::PTR_SLICE_FROM_RAW_PARTS_MUT, &[0]),
216 (&paths::PTR_SWAP, &[0, 1]),
217 (&paths::PTR_SWAP_NONOVERLAPPING, &[0, 1]),
218 (&paths::PTR_WRITE, &[0]),
219 (&paths::PTR_WRITE_UNALIGNED, &[0]),
220 (&paths::PTR_WRITE_VOLATILE, &[0]),
221 (&paths::PTR_WRITE_BYTES, &[0]),
225 if let ExprKind::Call(fun, args) = expr.kind;
226 if let ExprKind::Path(ref qpath) = fun.kind;
227 if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
228 let fun_def_path = cx.get_def_path(fun_def_id).into_iter().map(Symbol::to_ident_string).collect::<Vec<_>>();
229 if let Some(&(_, arg_indices)) = INVALID_NULL_PTR_USAGE_TABLE
231 .find(|&&(fn_path, _)| fn_path == fun_def_path);
233 for &arg_idx in arg_indices {
234 if let Some(arg) = args.get(arg_idx).filter(|arg| is_null_path(cx, arg)) {
237 INVALID_NULL_PTR_USAGE,
239 "pointer must be non-null",
241 "core::ptr::NonNull::dangling().as_ptr()".to_string(),
242 Applicability::MachineApplicable,
250 #[allow(clippy::too_many_lines)]
251 fn check_fn(cx: &LateContext<'_>, decl: &FnDecl<'_>, opt_body_id: Option<BodyId>) {
252 let body = opt_body_id.map(|id| cx.tcx.hir().body(id));
254 for (idx, arg) in decl.inputs.iter().enumerate() {
255 // Honor the allow attribute on parameters. See issue 5644.
256 if let Some(body) = &body {
257 if is_lint_allowed(cx, PTR_ARG, body.params[idx].hir_id) {
262 let (item_name, path) = if_chain! {
263 if let TyKind::Rptr(_, MutTy { ty, mutbl: Mutability::Not }) = arg.kind;
264 if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
265 if let Res::Def(_, did) = path.res;
266 if let Some(item_name) = cx.tcx.get_diagnostic_name(did);
276 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
281 "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
282 with non-Vec-based slices",
284 if let Some(ref snippet) = get_only_generic_arg_snippet(cx, arg) {
285 diag.span_suggestion(
288 format!("&[{}]", snippet),
289 Applicability::Unspecified,
292 for (clonespan, suggestion) in spans {
293 diag.span_suggestion(
295 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
296 Cow::Owned(format!("change `{}` to", x))
299 Applicability::Unspecified,
307 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
312 "writing `&String` instead of `&str` involves a new object where a slice will do",
314 diag.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
315 for (clonespan, suggestion) in spans {
316 diag.span_suggestion_short(
318 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
319 Cow::Owned(format!("change `{}` to", x))
322 Applicability::Unspecified,
330 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_path_buf()"), ("as_path", "")]) {
335 "writing `&PathBuf` instead of `&Path` involves a new object where a slice will do",
337 diag.span_suggestion(
341 Applicability::Unspecified,
343 for (clonespan, suggestion) in spans {
344 diag.span_suggestion_short(
346 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
347 Cow::Owned(format!("change `{}` to", x))
350 Applicability::Unspecified,
359 if let [ref bx] = *path.segments;
360 if let Some(params) = bx.args;
361 if !params.parenthesized;
362 if let Some(inner) = params.args.iter().find_map(|arg| match arg {
363 GenericArg::Type(ty) => Some(ty),
366 let replacement = snippet_opt(cx, inner.span);
367 if let Some(r) = replacement;
373 "using a reference to `Cow` is not recommended",
376 Applicability::Unspecified,
385 if let FnRetTy::Return(ty) = decl.output {
386 if let Some((out, Mutability::Mut, _)) = get_rptr_lm(ty) {
387 let mut immutables = vec![];
388 for (_, ref mutbl, ref argspan) in decl
391 .filter_map(get_rptr_lm)
392 .filter(|&(lt, _, _)| lt.name == out.name)
394 if *mutbl == Mutability::Mut {
397 immutables.push(*argspan);
399 if immutables.is_empty() {
406 "mutable borrow from immutable input(s)",
408 let ms = MultiSpan::from_spans(immutables);
409 diag.span_note(ms, "immutable borrow here");
416 fn get_only_generic_arg_snippet(cx: &LateContext<'_>, arg: &Ty<'_>) -> Option<String> {
418 if let TyKind::Path(QPath::Resolved(_, path)) = walk_ptrs_hir_ty(arg).kind;
419 if let Some(&PathSegment{args: Some(parameters), ..}) = path.segments.last();
420 let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
421 GenericArg::Type(ty) => Some(ty),
426 snippet_opt(cx, types[0].span)
433 fn get_rptr_lm<'tcx>(ty: &'tcx Ty<'tcx>) -> Option<(&'tcx Lifetime, Mutability, Span)> {
434 if let TyKind::Rptr(ref lt, ref m) = ty.kind {
435 Some((lt, m.mutbl, ty.span))
441 fn is_null_path(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
442 if let ExprKind::Call(pathexp, []) = expr.kind {
443 expr_path_res(cx, pathexp).opt_def_id().map_or(false, |id| {
444 match_any_diagnostic_items(cx, id, &[sym::ptr_null, sym::ptr_null_mut]).is_some()