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,
13 use utils::ptr::get_spans;
15 /// **What it does:** This lint checks for function arguments of type `&String`
16 /// or `&Vec` unless the references are mutable. It will also suggest you
17 /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
20 /// **Why is this bad?** Requiring the argument to be of the specific size
21 /// makes the function less useful for no benefit; slices in the form of `&[T]`
22 /// or `&str` usually suffice and can be obtained from other types, too.
24 /// **Known problems:** The lint does not follow data. So if you have an
25 /// argument `x` and write `let y = x; y.clone()` the lint will not suggest
26 /// changing that `.clone()` to `.to_owned()`.
28 /// Other functions called from this function taking a `&String` or `&Vec`
29 /// argument may also fail to compile if you change the argument. Applying
30 /// this lint on them will fix the problem, but they may be in other crates.
32 /// Also there may be `fn(&Vec)`-typed references pointing to your function.
33 /// If you have them, you will get a compiler error after applying this lint's
34 /// suggestions. You then have the choice to undo your changes or change the
35 /// type of the reference.
37 /// Note that if the function is part of your public interface, there may be
38 /// other crates referencing it you may not be aware. Carefully deprecate the
39 /// function before applying the lint suggestions in this case.
43 /// fn foo(&Vec<u32>) { .. }
48 "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` \
49 instead, respectively"
52 /// **What it does:** This lint checks for equality comparisons with `ptr::null`
54 /// **Why is this bad?** It's easier and more readable to use the inherent
58 /// **Known problems:** None.
62 /// if x == ptr::null { .. }
67 "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
70 /// **What it does:** This lint checks for functions that take immutable
71 /// references and return
74 /// **Why is this bad?** This is trivially unsound, as one can create two
75 /// mutable references
76 /// from the same (immutable!) source. This
77 /// [error](https://github.com/rust-lang/rust/issues/39465)
78 /// actually lead to an interim Rust release 1.15.1.
80 /// **Known problems:** To be on the conservative side, if there's at least one
82 /// with the output lifetime, this lint will not trigger. In practice, this
83 /// case is unlikely anyway.
87 /// fn foo(&Foo) -> &mut Bar { .. }
92 "fns that create mutable refs from immutable ref args"
95 #[derive(Copy, Clone)]
96 pub struct PointerPass;
98 impl LintPass for PointerPass {
99 fn get_lints(&self) -> LintArray {
100 lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF)
104 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass {
105 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
106 if let ItemFn(ref decl, _, _, _, _, body_id) = item.node {
107 check_fn(cx, decl, item.id, Some(body_id));
111 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
112 if let ImplItemKind::Method(ref sig, body_id) = item.node {
113 if let Some(NodeItem(it)) = cx.tcx.hir.find(cx.tcx.hir.get_parent(item.id)) {
114 if let ItemImpl(_, _, _, _, Some(_), _, _) = it.node {
115 return; // ignore trait impls
118 check_fn(cx, &sig.decl, item.id, Some(body_id));
122 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
123 if let TraitItemKind::Method(ref sig, ref trait_method) = item.node {
124 let body_id = if let TraitMethod::Provided(b) = *trait_method { Some(b) } else { None };
125 check_fn(cx, &sig.decl, item.id, body_id);
129 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
130 if let ExprBinary(ref op, ref l, ref r) = expr.node {
131 if (op.node == BiEq || op.node == BiNe) && (is_null_path(l) || is_null_path(r)) {
136 "Comparing with null is better expressed by the .is_null() method",
143 fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<BodyId>) {
144 let fn_def_id = cx.tcx.hir.local_def_id(fn_id);
145 let sig = cx.tcx.fn_sig(fn_def_id);
146 let fn_ty = sig.skip_binder();
148 for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
157 if match_type(cx, ty, &paths::VEC) {
158 let mut ty_snippet = None;
160 let TyPath(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node,
161 let Some(&PathSegment{parameters: Some(ref parameters), ..}) = path.segments.last(),
162 parameters.types.len() == 1,
164 ty_snippet = snippet_opt(cx, parameters.types[0].span);
166 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
171 "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
172 with non-Vec-based slices.",
174 if let Some(ref snippet) = ty_snippet {
175 db.span_suggestion(arg.span,
177 format!("&[{}]", snippet));
179 for (clonespan, suggestion) in spans {
180 db.span_suggestion(clonespan,
181 &snippet_opt(cx, clonespan).map_or("change the call to".into(),
182 |x| Cow::Owned(format!("change `{}` to", x))),
188 } else if match_type(cx, ty, &paths::STRING) {
189 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
194 "writing `&String` instead of `&str` involves a new object where a slice will do.",
196 db.span_suggestion(arg.span,
199 for (clonespan, suggestion) in spans {
200 db.span_suggestion_short(clonespan,
201 &snippet_opt(cx, clonespan).map_or("change the call to".into(),
202 |x| Cow::Owned(format!("change `{}` to", x))),
212 if let FunctionRetTy::Return(ref ty) = decl.output {
213 if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
214 let mut immutables = vec![];
215 for (_, ref mutbl, ref argspan) in decl.inputs
217 .filter_map(|ty| get_rptr_lm(ty))
218 .filter(|&(lt, _, _)| lt.name == out.name)
220 if *mutbl == MutMutable {
223 immutables.push(*argspan);
225 if immutables.is_empty() {
228 span_lint_and_then(cx, MUT_FROM_REF, ty.span, "mutable borrow from immutable input(s)", |db| {
229 let ms = MultiSpan::from_spans(immutables);
230 db.span_note(ms, "immutable borrow here");
236 fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
237 if let Ty_::TyRptr(ref lt, ref m) = ty.node {
238 Some((lt, m.mutbl, ty.span))
244 fn is_null_path(expr: &Expr) -> bool {
245 if let ExprCall(ref pathexp, ref args) = expr.node {
247 if let ExprPath(ref path) = pathexp.node {
248 return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);