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