1 //! Checks for usage of `&Vec[_]` and `&String`.
5 use rustc::hir::map::NodeItem;
8 use syntax::ast::NodeId;
9 use syntax::codemap::Span;
10 use syntax_pos::MultiSpan;
11 use utils::{match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then, walk_ptrs_hir_ty};
12 use utils::ptr::get_spans;
14 /// **What it does:** This lint checks for function arguments of type `&String`
15 /// or `&Vec` unless the references are mutable. It will also suggest you
16 /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
19 /// **Why is this bad?** Requiring the argument to be of the specific size
20 /// makes the function less useful for no benefit; slices in the form of `&[T]`
21 /// or `&str` usually suffice and can be obtained from other types, too.
23 /// **Known problems:** The lint does not follow data. So if you have an
24 /// argument `x` and write `let y = x; y.clone()` the lint will not suggest
25 /// changing that `.clone()` to `.to_owned()`.
27 /// Other functions called from this function taking a `&String` or `&Vec`
28 /// argument may also fail to compile if you change the argument. Applying
29 /// this lint on them will fix the problem, but they may be in other crates.
31 /// Also there may be `fn(&Vec)`-typed references pointing to your function.
32 /// If you have them, you will get a compiler error after applying this lint's
33 /// suggestions. You then have the choice to undo your changes or change the
34 /// type of the reference.
36 /// Note that if the function is part of your public interface, there may be
37 /// other crates referencing it you may not be aware. Carefully deprecate the
38 /// function before applying the lint suggestions in this case.
42 /// fn foo(&Vec<u32>) { .. }
47 "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` \
48 instead, respectively"
51 /// **What it does:** This lint checks for equality comparisons with `ptr::null`
53 /// **Why is this bad?** It's easier and more readable to use the inherent
57 /// **Known problems:** None.
61 /// if x == ptr::null { .. }
66 "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
69 /// **What it does:** This lint checks for functions that take immutable
70 /// references and return
73 /// **Why is this bad?** This is trivially unsound, as one can create two
74 /// mutable references
75 /// from the same (immutable!) source. This
76 /// [error](https://github.com/rust-lang/rust/issues/39465)
77 /// actually lead to an interim Rust release 1.15.1.
79 /// **Known problems:** To be on the conservative side, if there's at least one
81 /// with the output lifetime, this lint will not trigger. In practice, this
82 /// case is unlikely anyway.
86 /// fn foo(&Foo) -> &mut Bar { .. }
91 "fns that create mutable refs from immutable ref args"
94 #[derive(Copy, Clone)]
95 pub struct PointerPass;
97 impl LintPass for PointerPass {
98 fn get_lints(&self) -> LintArray {
99 lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF)
103 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass {
104 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
105 if let ItemFn(ref decl, _, _, _, _, body_id) = item.node {
106 check_fn(cx, decl, item.id, Some(body_id));
110 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
111 if let ImplItemKind::Method(ref sig, body_id) = item.node {
112 if let Some(NodeItem(it)) = cx.tcx.hir.find(cx.tcx.hir.get_parent(item.id)) {
113 if let ItemImpl(_, _, _, _, Some(_), _, _) = it.node {
114 return; // ignore trait impls
117 check_fn(cx, &sig.decl, item.id, Some(body_id));
121 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
122 if let TraitItemKind::Method(ref sig, ref trait_method) = item.node {
123 let body_id = if let TraitMethod::Provided(b) = *trait_method {
128 check_fn(cx, &sig.decl, item.id, body_id);
132 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
133 if let ExprBinary(ref op, ref l, ref r) = expr.node {
134 if (op.node == BiEq || op.node == BiNe) && (is_null_path(l) || is_null_path(r)) {
139 "Comparing with null is better expressed by the .is_null() method",
146 fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<BodyId>) {
147 let fn_def_id = cx.tcx.hir.local_def_id(fn_id);
148 let sig = cx.tcx.fn_sig(fn_def_id);
149 let fn_ty = sig.skip_binder();
151 for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
160 if match_type(cx, ty, &paths::VEC) {
161 let mut ty_snippet = None;
163 if let TyPath(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node;
164 if let Some(&PathSegment{parameters: Some(ref parameters), ..}) = path.segments.last();
165 if parameters.types.len() == 1;
167 ty_snippet = snippet_opt(cx, parameters.types[0].span);
170 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
175 "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
176 with non-Vec-based slices.",
178 if let Some(ref snippet) = ty_snippet {
179 db.span_suggestion(arg.span, "change this to", format!("&[{}]", snippet));
181 for (clonespan, suggestion) in spans {
184 &snippet_opt(cx, clonespan).map_or(
185 "change the call to".into(),
186 |x| Cow::Owned(format!("change `{}` to", x)),
194 } else if match_type(cx, ty, &paths::STRING) {
195 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
200 "writing `&String` instead of `&str` involves a new object where a slice will do.",
202 db.span_suggestion(arg.span, "change this to", "&str".into());
203 for (clonespan, suggestion) in spans {
204 db.span_suggestion_short(
206 &snippet_opt(cx, clonespan).map_or(
207 "change the call to".into(),
208 |x| Cow::Owned(format!("change `{}` to", x)),
220 if let FunctionRetTy::Return(ref ty) = decl.output {
221 if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
222 let mut immutables = vec![];
223 for (_, ref mutbl, ref argspan) in decl.inputs
225 .filter_map(|ty| get_rptr_lm(ty))
226 .filter(|&(lt, _, _)| lt.name == out.name)
228 if *mutbl == MutMutable {
231 immutables.push(*argspan);
233 if immutables.is_empty() {
236 span_lint_and_then(cx, MUT_FROM_REF, ty.span, "mutable borrow from immutable input(s)", |db| {
237 let ms = MultiSpan::from_spans(immutables);
238 db.span_note(ms, "immutable borrow here");
244 fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
245 if let Ty_::TyRptr(ref lt, ref m) = ty.node {
246 Some((lt, m.mutbl, ty.span))
252 fn is_null_path(expr: &Expr) -> bool {
253 if let ExprCall(ref pathexp, ref args) = expr.node {
255 if let ExprPath(ref path) = pathexp.node {
256 return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);