1 //! Checks for useless borrowed references.
3 //! This lint is **warn** by default
5 use crate::utils::{in_macro, snippet, span_lint_and_then};
6 use if_chain::if_chain;
7 use rustc::hir::{BindingAnnotation, MutImmutable, Pat, PatKind};
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
9 use rustc::{declare_tool_lint, lint_array};
10 use rustc_errors::Applicability;
12 declare_clippy_lint! {
13 /// **What it does:** Checks for useless borrowed references.
15 /// **Why is this bad?** It is mostly useless and make the code look more
19 /// **Known problems:** It seems that the `&ref` pattern is sometimes useful.
20 /// For instance in the following snippet:
27 /// fn foo(a: &Animal, b: &Animal) {
29 /// (&Animal::Cat(v), k) | (k, &Animal::Cat(v)) => (), // lifetime
31 /// (&Animal::Dog(ref c), &Animal::Dog(_)) => ()
35 /// There is a lifetime mismatch error for `k` (indeed a and b have distinct
37 /// This can be fixed by using the `&ref` pattern.
38 /// However, the code can also be fixed by much cleaner ways
42 /// let mut v = Vec::<String>::new();
43 /// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
45 /// This closure takes a reference on something that has been matched as a
48 /// As such, it could just be |a| a.is_empty()
49 pub NEEDLESS_BORROWED_REFERENCE,
51 "taking a needless borrowed reference"
54 #[derive(Copy, Clone)]
55 pub struct NeedlessBorrowedRef;
57 impl LintPass for NeedlessBorrowedRef {
58 fn get_lints(&self) -> LintArray {
59 lint_array!(NEEDLESS_BORROWED_REFERENCE)
62 fn name(&self) -> &'static str {
67 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrowedRef {
68 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
69 if in_macro(pat.span) {
70 // OK, simple enough, lints doesn't check in macro.
75 // Only lint immutable refs, because `&mut ref T` may be useful.
76 if let PatKind::Ref(ref sub_pat, MutImmutable) = pat.node;
78 // Check sub_pat got a `ref` keyword (excluding `ref mut`).
79 if let PatKind::Binding(BindingAnnotation::Ref, .., spanned_name, _) = sub_pat.node;
81 span_lint_and_then(cx, NEEDLESS_BORROWED_REFERENCE, pat.span,
82 "this pattern takes a reference on something that is being de-referenced",
84 let hint = snippet(cx, spanned_name.span, "..").into_owned();
87 "try removing the `&ref` part and just keep",
89 Applicability::MachineApplicable, // snippet