1 //! Checks for useless borrowed references.
3 //! This lint is **warn** by default
6 use rustc::hir::{MutImmutable, Pat, PatKind, BindingAnnotation};
8 use utils::{span_lint, in_macro};
10 /// **What it does:** Checks for useless borrowed references.
12 /// **Why is this bad?** It is completely useless and make the code look more
16 /// **Known problems:** None.
20 /// let mut v = Vec::<String>::new();
21 /// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
23 /// This clojure takes a reference on something that has been matched as a
26 /// As such, it could just be |a| a.is_empty()
28 pub NEEDLESS_BORROWED_REFERENCE,
30 "taking a needless borrowed reference"
33 #[derive(Copy, Clone)]
34 pub struct NeedlessBorrowedRef;
36 impl LintPass for NeedlessBorrowedRef {
37 fn get_lints(&self) -> LintArray {
38 lint_array!(NEEDLESS_BORROWED_REFERENCE)
42 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrowedRef {
43 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
44 if in_macro(pat.span) {
45 // OK, simple enough, lints doesn't check in macro.
50 // Pat is a pattern whose node
51 // is a binding which "involves" an immutable reference...
52 let PatKind::Binding(BindingAnnotation::Ref, ..) = pat.node,
53 // Pattern's type is a reference. Get the type and mutability of referenced value (tam: TypeAndMut).
54 let ty::TyRef(_, ref tam) = cx.tables.pat_ty(pat).sty,
55 // Only lint immutable refs, because `&mut ref T` may be useful.
56 tam.mutbl == MutImmutable,
58 span_lint(cx, NEEDLESS_BORROWED_REFERENCE, pat.span, "this pattern takes a reference on something that is being de-referenced")