1 //! Checks for useless borrowed references.
3 //! This lint is **warn** by default
6 use rustc::hir::{BindingAnnotation, MutImmutable, Pat, PatKind};
7 use utils::{in_macro, snippet, span_lint_and_then};
9 /// **What it does:** Checks for useless borrowed references.
11 /// **Why is this bad?** It is mostly useless and make the code look more
15 /// **Known problems:** It seems that the `&ref` pattern is sometimes useful.
16 /// For instance in the following snippet:
23 /// fn foo(a: &Animal, b: &Animal) {
25 /// (&Animal::Cat(v), k) | (k, &Animal::Cat(v)) => (), // lifetime
27 /// (&Animal::Dog(ref c), &Animal::Dog(_)) => ()
31 /// There is a lifetime mismatch error for `k` (indeed a and b have distinct
33 /// This can be fixed by using the `&ref` pattern.
34 /// However, the code can also be fixed by much cleaner ways
38 /// let mut v = Vec::<String>::new();
39 /// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
41 /// This clojure takes a reference on something that has been matched as a
44 /// As such, it could just be |a| a.is_empty()
46 pub NEEDLESS_BORROWED_REFERENCE,
48 "taking a needless borrowed reference"
51 #[derive(Copy, Clone)]
52 pub struct NeedlessBorrowedRef;
54 impl LintPass for NeedlessBorrowedRef {
55 fn get_lints(&self) -> LintArray {
56 lint_array!(NEEDLESS_BORROWED_REFERENCE)
60 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrowedRef {
61 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
62 if in_macro(pat.span) {
63 // OK, simple enough, lints doesn't check in macro.
68 // Only lint immutable refs, because `&mut ref T` may be useful.
69 if let PatKind::Ref(ref sub_pat, MutImmutable) = pat.node;
71 // Check sub_pat got a `ref` keyword (excluding `ref mut`).
72 if let PatKind::Binding(BindingAnnotation::Ref, _, spanned_name, ..) = sub_pat.node;
74 span_lint_and_then(cx, NEEDLESS_BORROWED_REFERENCE, pat.span,
75 "this pattern takes a reference on something that is being de-referenced",
77 let hint = snippet(cx, spanned_name.span, "..").into_owned();
78 db.span_suggestion(pat.span, "try removing the `&ref` part and just keep", hint);