1 //! Checks for usage of `&Vec[_]` and `&String`.
5 use rustc::hir::map::NodeItem;
8 use rustc::{declare_lint, lint_array};
9 use if_chain::if_chain;
11 use syntax::ast::NodeId;
12 use syntax::source_map::Span;
13 use syntax_pos::MultiSpan;
14 use crate::utils::{match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then, walk_ptrs_hir_ty};
15 use crate::utils::ptr::get_spans;
17 /// **What it does:** This lint checks for function arguments of type `&String`
18 /// or `&Vec` unless the references are mutable. It will also suggest you
19 /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
22 /// **Why is this bad?** Requiring the argument to be of the specific size
23 /// makes the function less useful for no benefit; slices in the form of `&[T]`
24 /// or `&str` usually suffice and can be obtained from other types, too.
26 /// **Known problems:** The lint does not follow data. So if you have an
27 /// argument `x` and write `let y = x; y.clone()` the lint will not suggest
28 /// changing that `.clone()` to `.to_owned()`.
30 /// Other functions called from this function taking a `&String` or `&Vec`
31 /// argument may also fail to compile if you change the argument. Applying
32 /// this lint on them will fix the problem, but they may be in other crates.
34 /// Also there may be `fn(&Vec)`-typed references pointing to your function.
35 /// If you have them, you will get a compiler error after applying this lint's
36 /// suggestions. You then have the choice to undo your changes or change the
37 /// type of the reference.
39 /// Note that if the function is part of your public interface, there may be
40 /// other crates referencing it you may not be aware. Carefully deprecate the
41 /// function before applying the lint suggestions in this case.
45 /// fn foo(&Vec<u32>) { .. }
47 declare_clippy_lint! {
50 "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` \
51 instead, respectively"
54 /// **What it does:** This lint checks for equality comparisons with `ptr::null`
56 /// **Why is this bad?** It's easier and more readable to use the inherent
60 /// **Known problems:** None.
64 /// if x == ptr::null { .. }
66 declare_clippy_lint! {
69 "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
72 /// **What it does:** This lint checks for functions that take immutable
73 /// references and return
76 /// **Why is this bad?** This is trivially unsound, as one can create two
77 /// mutable references
78 /// from the same (immutable!) source. This
79 /// [error](https://github.com/rust-lang/rust/issues/39465)
80 /// actually lead to an interim Rust release 1.15.1.
82 /// **Known problems:** To be on the conservative side, if there's at least one
84 /// with the output lifetime, this lint will not trigger. In practice, this
85 /// case is unlikely anyway.
89 /// fn foo(&Foo) -> &mut Bar { .. }
91 declare_clippy_lint! {
94 "fns that create mutable refs from immutable ref args"
97 #[derive(Copy, Clone)]
98 pub struct PointerPass;
100 impl LintPass for PointerPass {
101 fn get_lints(&self) -> LintArray {
102 lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF)
106 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass {
107 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
108 if let ItemKind::Fn(ref decl, _, _, body_id) = item.node {
109 check_fn(cx, decl, item.id, Some(body_id));
113 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
114 if let ImplItemKind::Method(ref sig, body_id) = item.node {
115 if let Some(NodeItem(it)) = cx.tcx.hir.find(cx.tcx.hir.get_parent(item.id)) {
116 if let ItemKind::Impl(_, _, _, _, Some(_), _, _) = it.node {
117 return; // ignore trait impls
120 check_fn(cx, &sig.decl, item.id, Some(body_id));
124 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
125 if let TraitItemKind::Method(ref sig, ref trait_method) = item.node {
126 let body_id = if let TraitMethod::Provided(b) = *trait_method {
131 check_fn(cx, &sig.decl, item.id, body_id);
135 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
136 if let ExprKind::Binary(ref op, ref l, ref r) = expr.node {
137 if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(l) || is_null_path(r)) {
142 "Comparing with null is better expressed by the .is_null() method",
149 fn check_fn(cx: &LateContext<'_, '_>, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<BodyId>) {
150 let fn_def_id = cx.tcx.hir.local_def_id(fn_id);
151 let sig = cx.tcx.fn_sig(fn_def_id);
152 let fn_ty = sig.skip_binder();
154 for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
161 if match_type(cx, ty, &paths::VEC) {
162 let mut ty_snippet = None;
164 if let TyKind::Path(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node;
165 if let Some(&PathSegment{args: Some(ref parameters), ..}) = path.segments.last();
167 let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
168 GenericArg::Type(ty) => Some(ty),
171 if types.len() == 1 {
172 ty_snippet = snippet_opt(cx, types[0].span);
176 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
181 "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
182 with non-Vec-based slices.",
184 if let Some(ref snippet) = ty_snippet {
185 db.span_suggestion(arg.span, "change this to", format!("&[{}]", snippet));
187 for (clonespan, suggestion) in spans {
190 &snippet_opt(cx, clonespan).map_or(
191 "change the call to".into(),
192 |x| Cow::Owned(format!("change `{}` to", x)),
200 } else if match_type(cx, ty, &paths::STRING) {
201 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
206 "writing `&String` instead of `&str` involves a new object where a slice will do.",
208 db.span_suggestion(arg.span, "change this to", "&str".into());
209 for (clonespan, suggestion) in spans {
210 db.span_suggestion_short(
212 &snippet_opt(cx, clonespan).map_or(
213 "change the call to".into(),
214 |x| Cow::Owned(format!("change `{}` to", x)),
222 } else if match_type(cx, ty, &paths::COW) {
224 if let TyKind::Rptr(_, MutTy { ref ty, ..} ) = arg.node;
225 if let TyKind::Path(ref path) = ty.node;
226 if let QPath::Resolved(None, ref pp) = *path;
227 if let [ref bx] = *pp.segments;
228 if let Some(ref params) = bx.args;
229 if !params.parenthesized;
230 if let Some(inner) = params.args.iter().find_map(|arg| match arg {
231 GenericArg::Type(ty) => Some(ty),
232 GenericArg::Lifetime(_) => None,
235 let replacement = snippet_opt(cx, inner.span);
236 if let Some(r) = replacement {
241 "using a reference to `Cow` is not recommended.",
243 db.span_suggestion(arg.span, "change this to", "&".to_owned() + &r);
253 if let FunctionRetTy::Return(ref ty) = decl.output {
254 if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
255 let mut immutables = vec![];
256 for (_, ref mutbl, ref argspan) in decl.inputs
258 .filter_map(|ty| get_rptr_lm(ty))
259 .filter(|&(lt, _, _)| lt.name == out.name)
261 if *mutbl == MutMutable {
264 immutables.push(*argspan);
266 if immutables.is_empty() {
269 span_lint_and_then(cx, MUT_FROM_REF, ty.span, "mutable borrow from immutable input(s)", |db| {
270 let ms = MultiSpan::from_spans(immutables);
271 db.span_note(ms, "immutable borrow here");
277 fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
278 if let TyKind::Rptr(ref lt, ref m) = ty.node {
279 Some((lt, m.mutbl, ty.span))
285 fn is_null_path(expr: &Expr) -> bool {
286 if let ExprKind::Call(ref pathexp, ref args) = expr.node {
288 if let ExprKind::Path(ref path) = pathexp.node {
289 return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);