1 //! Checks for usage of `&Vec[_]` and `&String`.
3 use crate::utils::ptr::get_spans;
4 use crate::utils::{match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then, walk_ptrs_hir_ty};
5 use if_chain::if_chain;
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
10 use rustc::{declare_tool_lint, lint_array};
11 use rustc_errors::Applicability;
13 use syntax::ast::NodeId;
14 use syntax::source_map::Span;
15 use syntax_pos::MultiSpan;
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` 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 {
67 declare_clippy_lint! {
70 "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
73 /// **What it does:** This lint checks for functions that take immutable
74 /// references and return
77 /// **Why is this bad?** This is trivially unsound, as one can create two
78 /// mutable references
79 /// from the same (immutable!) source. This
80 /// [error](https://github.com/rust-lang/rust/issues/39465)
81 /// actually lead to an interim Rust release 1.15.1.
83 /// **Known problems:** To be on the conservative side, if there's at least one
85 /// with the output lifetime, this lint will not trigger. In practice, this
86 /// case is unlikely anyway.
90 /// fn foo(&Foo) -> &mut Bar { .. }
92 declare_clippy_lint! {
95 "fns that create mutable refs from immutable ref args"
98 #[derive(Copy, Clone)]
99 pub struct PointerPass;
101 impl LintPass for PointerPass {
102 fn get_lints(&self) -> LintArray {
103 lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF)
106 fn name(&self) -> &'static str {
111 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass {
112 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
113 if let ItemKind::Fn(ref decl, _, _, body_id) = item.node {
114 check_fn(cx, decl, item.id, Some(body_id));
118 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
119 if let ImplItemKind::Method(ref sig, body_id) = item.node {
120 if let Some(Node::Item(it)) = cx.tcx.hir().find(cx.tcx.hir().get_parent(item.id)) {
121 if let ItemKind::Impl(_, _, _, _, Some(_), _, _) = it.node {
122 return; // ignore trait impls
125 check_fn(cx, &sig.decl, item.id, Some(body_id));
129 fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
130 if let TraitItemKind::Method(ref sig, ref trait_method) = item.node {
131 let body_id = if let TraitMethod::Provided(b) = *trait_method {
136 check_fn(cx, &sig.decl, item.id, body_id);
140 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
141 if let ExprKind::Binary(ref op, ref l, ref r) = expr.node {
142 if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(l) || is_null_path(r)) {
147 "Comparing with null is better expressed by the .is_null() method",
154 #[allow(clippy::too_many_lines)]
155 fn check_fn(cx: &LateContext<'_, '_>, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<BodyId>) {
156 let fn_def_id = cx.tcx.hir().local_def_id(fn_id);
157 let sig = cx.tcx.fn_sig(fn_def_id);
158 let fn_ty = sig.skip_binder();
160 for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
161 if let ty::Ref(_, ty, MutImmutable) = ty.sty {
162 if match_type(cx, ty, &paths::VEC) {
163 let mut ty_snippet = None;
165 if let TyKind::Path(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node;
166 if let Some(&PathSegment{args: Some(ref parameters), ..}) = path.segments.last();
168 let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
169 GenericArg::Type(ty) => Some(ty),
172 if types.len() == 1 {
173 ty_snippet = snippet_opt(cx, types[0].span);
177 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
182 "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
183 with non-Vec-based slices.",
185 if let Some(ref snippet) = ty_snippet {
189 format!("&[{}]", snippet),
190 Applicability::Unspecified,
193 for (clonespan, suggestion) in spans {
196 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
197 Cow::Owned(format!("change `{}` to", x))
200 Applicability::Unspecified,
206 } else if match_type(cx, ty, &paths::STRING) {
207 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
212 "writing `&String` instead of `&str` involves a new object where a slice will do.",
214 db.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
215 for (clonespan, suggestion) in spans {
216 db.span_suggestion_short(
218 &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
219 Cow::Owned(format!("change `{}` to", x))
222 Applicability::Unspecified,
228 } else if match_type(cx, ty, &paths::COW) {
230 if let TyKind::Rptr(_, MutTy { ref ty, ..} ) = arg.node;
231 if let TyKind::Path(ref path) = ty.node;
232 if let QPath::Resolved(None, ref pp) = *path;
233 if let [ref bx] = *pp.segments;
234 if let Some(ref params) = bx.args;
235 if !params.parenthesized;
236 if let Some(inner) = params.args.iter().find_map(|arg| match arg {
237 GenericArg::Type(ty) => Some(ty),
241 let replacement = snippet_opt(cx, inner.span);
242 if let Some(r) = replacement {
247 "using a reference to `Cow` is not recommended.",
253 Applicability::Unspecified,
264 if let FunctionRetTy::Return(ref ty) = decl.output {
265 if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
266 let mut immutables = vec![];
267 for (_, ref mutbl, ref argspan) in decl
270 .filter_map(|ty| get_rptr_lm(ty))
271 .filter(|&(lt, _, _)| lt.name == out.name)
273 if *mutbl == MutMutable {
276 immutables.push(*argspan);
278 if immutables.is_empty() {
285 "mutable borrow from immutable input(s)",
287 let ms = MultiSpan::from_spans(immutables);
288 db.span_note(ms, "immutable borrow here");
295 fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
296 if let TyKind::Rptr(ref lt, ref m) = ty.node {
297 Some((lt, m.mutbl, ty.span))
303 fn is_null_path(expr: &Expr) -> bool {
304 if let ExprKind::Call(ref pathexp, ref args) = expr.node {
306 if let ExprKind::Path(ref path) = pathexp.node {
307 return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);