1 //! Checks for useless borrowed references.
3 //! This lint is **warn** by default
6 use rustc::hir::{MutImmutable, Pat, PatKind, BindingMode};
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 complex than it actually is.
14 /// **Known problems:** None.
18 /// let mut v = Vec::<String>::new();
19 /// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
21 /// This clojure takes a reference on something that has been matched as a reference and de-referenced.
22 /// As such, it could just be |a| a.is_empty()
24 pub NEEDLESS_BORROWED_REFERENCE,
26 "taking a needless borrowed reference"
29 #[derive(Copy, Clone)]
30 pub struct NeedlessBorrowedRef;
32 impl LintPass for NeedlessBorrowedRef {
33 fn get_lints(&self) -> LintArray {
34 lint_array!(NEEDLESS_BORROWED_REFERENCE)
38 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrowedRef {
39 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
40 if in_macro(pat.span) {
41 // OK, simple enough, lints doesn't check in macro.
46 // Pat is a pattern whose node
47 // is a binding which "involves" a immutable reference...
48 let PatKind::Binding(BindingMode::BindByRef(MutImmutable), ..) = pat.node,
49 // Pattern's type is a reference. Get the type and mutability of referenced value (tam: TypeAndMut).
50 let ty::TyRef(_, ref tam) = cx.tables.pat_ty(pat).sty,
51 // This is an immutable reference.
52 tam.mutbl == MutImmutable,
54 span_lint(cx, NEEDLESS_BORROWED_REFERENCE, pat.span, "this pattern takes a reference on something that is being de-referenced")