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]) { .. }
75 "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
78 declare_clippy_lint! {
80 /// This lint checks for equality comparisons with `ptr::null`
82 /// ### Why is this bad?
83 /// It's easier and more readable to use the inherent
90 /// if x == ptr::null {
101 "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead"
104 declare_clippy_lint! {
106 /// This lint checks for functions that take immutable
107 /// references and return mutable ones.
109 /// ### Why is this bad?
110 /// This is trivially unsound, as one can create two
111 /// mutable references from the same (immutable!) source.
112 /// This [error](https://github.com/rust-lang/rust/issues/39465)
113 /// actually lead to an interim Rust release 1.15.1.
115 /// ### Known problems
116 /// To be on the conservative side, if there's at least one
117 /// mutable reference with the output lifetime, this lint will not trigger.
118 /// In practice, this case is unlikely anyway.
122 /// fn foo(&Foo) -> &mut Bar { .. }
126 "fns that create mutable refs from immutable ref args"
129 declare_clippy_lint! {
131 /// This lint checks for invalid usages of `ptr::null`.
133 /// ### Why is this bad?
134 /// This causes undefined behavior.
138 /// // Bad. Undefined behavior
139 /// unsafe { std::slice::from_raw_parts(ptr::null(), 0); }
144 /// unsafe { std::slice::from_raw_parts(NonNull::dangling().as_ptr(), 0); }
146 pub INVALID_NULL_PTR_USAGE,
148 "invalid usage of a null pointer, suggesting `NonNull::dangling()` instead"
151 declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF, INVALID_NULL_PTR_USAGE]);
153 impl<'tcx> LateLintPass<'tcx> for Ptr {
154 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
155 if let ItemKind::Fn(ref sig, _, body_id) = item.kind {
156 check_fn(cx, sig.decl, Some(body_id));
160 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
161 if let ImplItemKind::Fn(ref sig, body_id) = item.kind {
162 let parent_item = cx.tcx.hir().get_parent_item(item.hir_id());
163 if let Some(Node::Item(it)) = cx.tcx.hir().find(parent_item) {
164 if let ItemKind::Impl(Impl { of_trait: Some(_), .. }) = it.kind {
165 return; // ignore trait impls
168 check_fn(cx, sig.decl, Some(body_id));
172 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
173 if let TraitItemKind::Fn(ref sig, ref trait_method) = item.kind {
174 let body_id = if let TraitFn::Provided(b) = *trait_method {
179 check_fn(cx, sig.decl, body_id);
183 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
184 if let ExprKind::Binary(ref op, l, r) = expr.kind {
185 if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(cx, l) || is_null_path(cx, r)) {
190 "comparing with null is better expressed by the `.is_null()` method",
194 check_invalid_ptr_usage(cx, expr);
199 fn check_invalid_ptr_usage<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
200 // (fn_path, arg_indices) - `arg_indices` are the `arg` positions where null would cause U.B.
201 const INVALID_NULL_PTR_USAGE_TABLE: [(&[&str], &[usize]); 16] = [
202 (&paths::SLICE_FROM_RAW_PARTS, &[0]),
203 (&paths::SLICE_FROM_RAW_PARTS_MUT, &[0]),
204 (&paths::PTR_COPY, &[0, 1]),
205 (&paths::PTR_COPY_NONOVERLAPPING, &[0, 1]),
206 (&paths::PTR_READ, &[0]),
207 (&paths::PTR_READ_UNALIGNED, &[0]),
208 (&paths::PTR_READ_VOLATILE, &[0]),
209 (&paths::PTR_REPLACE, &[0]),
210 (&paths::PTR_SLICE_FROM_RAW_PARTS, &[0]),
211 (&paths::PTR_SLICE_FROM_RAW_PARTS_MUT, &[0]),
212 (&paths::PTR_SWAP, &[0, 1]),
213 (&paths::PTR_SWAP_NONOVERLAPPING, &[0, 1]),
214 (&paths::PTR_WRITE, &[0]),
215 (&paths::PTR_WRITE_UNALIGNED, &[0]),
216 (&paths::PTR_WRITE_VOLATILE, &[0]),
217 (&paths::PTR_WRITE_BYTES, &[0]),
221 if let ExprKind::Call(fun, args) = expr.kind;
222 if let ExprKind::Path(ref qpath) = fun.kind;
223 if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
224 let fun_def_path = cx.get_def_path(fun_def_id).into_iter().map(Symbol::to_ident_string).collect::<Vec<_>>();
225 if let Some(&(_, arg_indices)) = INVALID_NULL_PTR_USAGE_TABLE
227 .find(|&&(fn_path, _)| fn_path == fun_def_path);
229 for &arg_idx in arg_indices {
230 if let Some(arg) = args.get(arg_idx).filter(|arg| is_null_path(cx, arg)) {
233 INVALID_NULL_PTR_USAGE,
235 "pointer must be non-null",
237 "core::ptr::NonNull::dangling().as_ptr()".to_string(),
238 Applicability::MachineApplicable,
246 #[allow(clippy::too_many_lines)]
247 fn check_fn(cx: &LateContext<'_>, decl: &FnDecl<'_>, opt_body_id: Option<BodyId>) {
248 let body = opt_body_id.map(|id| cx.tcx.hir().body(id));
250 for (idx, arg) in decl.inputs.iter().enumerate() {
251 // Honor the allow attribute on parameters. See issue 5644.
252 if let Some(body) = &body {
253 if is_lint_allowed(cx, PTR_ARG, body.params[idx].hir_id) {
258 let (item_name, path) = if_chain! {
259 if let TyKind::Rptr(_, MutTy { ty, mutbl: Mutability::Not }) = arg.kind;
260 if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
261 if let Res::Def(_, did) = path.res;
262 if let Some(item_name) = cx.tcx.get_diagnostic_name(did);
272 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
277 "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
278 with non-Vec-based slices",
280 if let Some(ref snippet) = get_only_generic_arg_snippet(cx, arg) {
281 diag.span_suggestion(
284 format!("&[{}]", snippet),
285 Applicability::Unspecified,
288 for (clonespan, suggestion) in spans {
289 diag.span_suggestion(
291 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
292 Cow::Owned(format!("change `{}` to", x))
295 Applicability::Unspecified,
303 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
308 "writing `&String` instead of `&str` involves a new object where a slice will do",
310 diag.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
311 for (clonespan, suggestion) in spans {
312 diag.span_suggestion_short(
314 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
315 Cow::Owned(format!("change `{}` to", x))
318 Applicability::Unspecified,
326 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_path_buf()"), ("as_path", "")]) {
331 "writing `&PathBuf` instead of `&Path` involves a new object where a slice will do",
333 diag.span_suggestion(
337 Applicability::Unspecified,
339 for (clonespan, suggestion) in spans {
340 diag.span_suggestion_short(
342 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
343 Cow::Owned(format!("change `{}` to", x))
346 Applicability::Unspecified,
355 if let [ref bx] = *path.segments;
356 if let Some(params) = bx.args;
357 if !params.parenthesized;
358 if let Some(inner) = params.args.iter().find_map(|arg| match arg {
359 GenericArg::Type(ty) => Some(ty),
362 let replacement = snippet_opt(cx, inner.span);
363 if let Some(r) = replacement;
369 "using a reference to `Cow` is not recommended",
372 Applicability::Unspecified,
381 if let FnRetTy::Return(ty) = decl.output {
382 if let Some((out, Mutability::Mut, _)) = get_rptr_lm(ty) {
383 let mut immutables = vec![];
384 for (_, ref mutbl, ref argspan) in decl
387 .filter_map(get_rptr_lm)
388 .filter(|&(lt, _, _)| lt.name == out.name)
390 if *mutbl == Mutability::Mut {
393 immutables.push(*argspan);
395 if immutables.is_empty() {
402 "mutable borrow from immutable input(s)",
404 let ms = MultiSpan::from_spans(immutables);
405 diag.span_note(ms, "immutable borrow here");
412 fn get_only_generic_arg_snippet(cx: &LateContext<'_>, arg: &Ty<'_>) -> Option<String> {
414 if let TyKind::Path(QPath::Resolved(_, path)) = walk_ptrs_hir_ty(arg).kind;
415 if let Some(&PathSegment{args: Some(parameters), ..}) = path.segments.last();
416 let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
417 GenericArg::Type(ty) => Some(ty),
422 snippet_opt(cx, types[0].span)
429 fn get_rptr_lm<'tcx>(ty: &'tcx Ty<'tcx>) -> Option<(&'tcx Lifetime, Mutability, Span)> {
430 if let TyKind::Rptr(ref lt, ref m) = ty.kind {
431 Some((lt, m.mutbl, ty.span))
437 fn is_null_path(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
438 if let ExprKind::Call(pathexp, []) = expr.kind {
439 expr_path_res(cx, pathexp).opt_def_id().map_or(false, |id| {
440 match_any_diagnostic_items(cx, id, &[sym::ptr_null, sym::ptr_null_mut]).is_some()