1 //! Checks for usage of `&Vec[_]` and `&String`.
5 use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
6 use rustc::hir::map::NodeItem;
9 use syntax::ast::{Name, NodeId};
10 use syntax::codemap::Span;
11 use syntax_pos::MultiSpan;
12 use utils::{get_pat_name, match_qpath, match_type, match_var, paths,
13 snippet, snippet_opt, span_lint, span_lint_and_then,
16 /// **What it does:** This lint checks for function arguments of type `&String`
17 /// or `&Vec` unless the references are mutable. It will also suggest you
18 /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
21 /// **Why is this bad?** Requiring the argument to be of the specific size
22 /// makes the function less useful for no benefit; slices in the form of `&[T]`
23 /// or `&str` usually suffice and can be obtained from other types, too.
25 /// **Known problems:** The lint does not follow data. So if you have an
26 /// argument `x` and write `let y = x; y.clone()` the lint will not suggest
27 /// changing that `.clone()` to `.to_owned()`.
29 /// Other functions called from this function taking a `&String` or `&Vec`
30 /// argument may also fail to compile if you change the argument. Applying
31 /// this lint on them will fix the problem, but they may be in other crates.
33 /// Also there may be `fn(&Vec)`-typed references pointing to your function.
34 /// If you have them, you will get a compiler error after applying this lint's
35 /// suggestions. You then have the choice to undo your changes or change the
36 /// type of the reference.
38 /// Note that if the function is part of your public interface, there may be
39 /// other crates referencing it you may not be aware. Carefully deprecate the
40 /// function before applying the lint suggestions in this case.
44 /// fn foo(&Vec<u32>) { .. }
49 "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` \
50 instead, respectively"
53 /// **What it does:** This lint checks for equality comparisons with `ptr::null`
55 /// **Why is this bad?** It's easier and more readable to use the inherent
59 /// **Known problems:** None.
63 /// if x == ptr::null { .. }
68 "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
71 /// **What it does:** This lint checks for functions that take immutable
72 /// references and return
75 /// **Why is this bad?** This is trivially unsound, as one can create two
76 /// mutable references
77 /// from the same (immutable!) source. This
78 /// [error](https://github.com/rust-lang/rust/issues/39465)
79 /// actually lead to an interim Rust release 1.15.1.
81 /// **Known problems:** To be on the conservative side, if there's at least one
83 /// with the output lifetime, this lint will not trigger. In practice, this
84 /// case is unlikely anyway.
88 /// fn foo(&Foo) -> &mut Bar { .. }
93 "fns that create mutable refs from immutable ref args"
96 #[derive(Copy, Clone)]
97 pub struct PointerPass;
99 impl LintPass for PointerPass {
100 fn get_lints(&self) -> LintArray {
101 lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF)
105 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass {
106 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
107 if let ItemFn(ref decl, _, _, _, _, body_id) = item.node {
108 check_fn(cx, decl, item.id, Some(body_id));
112 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
113 if let ImplItemKind::Method(ref sig, body_id) = item.node {
114 if let Some(NodeItem(it)) = cx.tcx.hir.find(cx.tcx.hir.get_parent(item.id)) {
115 if let ItemImpl(_, _, _, _, Some(_), _, _) = it.node {
116 return; // ignore trait impls
119 check_fn(cx, &sig.decl, item.id, Some(body_id));
123 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
124 if let TraitItemKind::Method(ref sig, ref trait_method) = item.node {
125 let body_id = if let TraitMethod::Provided(b) = *trait_method { Some(b) } else { None };
126 check_fn(cx, &sig.decl, item.id, body_id);
130 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
131 if let ExprBinary(ref op, ref l, ref r) = expr.node {
132 if (op.node == BiEq || op.node == BiNe) && (is_null_path(l) || is_null_path(r)) {
137 "Comparing with null is better expressed by the .is_null() method",
144 fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<BodyId>) {
145 let fn_def_id = cx.tcx.hir.local_def_id(fn_id);
146 let sig = cx.tcx.fn_sig(fn_def_id);
147 let fn_ty = sig.skip_binder();
149 for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
158 if match_type(cx, ty, &paths::VEC) {
159 let mut ty_snippet = None;
161 let TyPath(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node,
162 let Some(&PathSegment{ref parameters, ..}) = path.segments.last(),
163 parameters.types.len() == 1,
165 ty_snippet = snippet_opt(cx, parameters.types[0].span);
167 if let Ok(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
172 "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
173 with non-Vec-based slices.",
175 if let Some(ref snippet) = ty_snippet {
176 db.span_suggestion(arg.span,
178 format!("&[{}]", snippet));
180 for (clonespan, suggestion) in spans {
181 db.span_suggestion(clonespan,
182 &snippet_opt(cx, clonespan).map_or("change the call to".into(),
183 |x| Cow::Owned(format!("change `{}` to", x))),
189 } else if match_type(cx, ty, &paths::STRING) {
190 if let Ok(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
195 "writing `&String` instead of `&str` involves a new object where a slice will do.",
197 db.span_suggestion(arg.span,
200 for (clonespan, suggestion) in spans {
201 db.span_suggestion_short(clonespan,
202 &snippet_opt(cx, clonespan).map_or("change the call to".into(),
203 |x| Cow::Owned(format!("change `{}` to", x))),
213 if let FunctionRetTy::Return(ref ty) = decl.output {
214 if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
215 let mut immutables = vec![];
216 for (_, ref mutbl, ref argspan) in decl.inputs
218 .filter_map(|ty| get_rptr_lm(ty))
219 .filter(|&(lt, _, _)| lt.name == out.name)
221 if *mutbl == MutMutable {
224 immutables.push(*argspan);
226 if immutables.is_empty() {
229 span_lint_and_then(cx, MUT_FROM_REF, ty.span, "mutable borrow from immutable input(s)", |db| {
230 let ms = MultiSpan::from_spans(immutables);
231 db.span_note(ms, "immutable borrow here");
237 fn get_spans(cx: &LateContext, opt_body_id: Option<BodyId>, idx: usize, replacements: &'static [(&'static str, &'static str)]) -> Result<Vec<(Span, Cow<'static, str>)>, ()> {
238 if let Some(body) = opt_body_id.map(|id| cx.tcx.hir.body(id)) {
239 get_binding_name(&body.arguments[idx]).map_or_else(|| Ok(vec![]),
240 |name| extract_clone_suggestions(cx, name, replacements, body))
246 fn extract_clone_suggestions<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, name: Name, replace: &'static [(&'static str, &'static str)], body: &'tcx Body) -> Result<Vec<(Span, Cow<'static, str>)>, ()> {
247 let mut visitor = PtrCloneVisitor {
254 visitor.visit_body(body);
255 if visitor.abort { Err(()) } else { Ok(visitor.spans) }
258 struct PtrCloneVisitor<'a, 'tcx: 'a> {
259 cx: &'a LateContext<'a, 'tcx>,
261 replace: &'static [(&'static str, &'static str)],
262 spans: Vec<(Span, Cow<'static, str>)>,
266 impl<'a, 'tcx: 'a> Visitor<'tcx> for PtrCloneVisitor<'a, 'tcx> {
267 fn visit_expr(&mut self, expr: &'tcx Expr) {
268 if self.abort { return; }
269 if let ExprMethodCall(ref seg, _, ref args) = expr.node {
270 if args.len() == 1 && match_var(&args[0], self.name) {
271 if seg.name == "capacity" {
275 for &(fn_name, suffix) in self.replace {
276 if seg.name == fn_name {
277 self.spans.push((expr.span, snippet(self.cx, args[0].span, "_") + suffix));
284 walk_expr(self, expr);
287 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
288 NestedVisitorMap::None
293 fn get_binding_name(arg: &Arg) -> Option<Name> {
294 get_pat_name(&arg.pat)
297 fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
298 if let Ty_::TyRptr(ref lt, ref m) = ty.node {
299 Some((lt, m.mutbl, ty.span))
305 fn is_null_path(expr: &Expr) -> bool {
306 if let ExprCall(ref pathexp, ref args) = expr.node {
308 if let ExprPath(ref path) = pathexp.node {
309 return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);