1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::source::snippet_with_applicability;
3 use if_chain::if_chain;
4 use rustc_errors::Applicability;
5 use rustc_hir::{BindingAnnotation, Mutability, Node, Pat, PatKind};
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 /// Checks for bindings that destructure a reference and borrow the inner
12 /// value with `&ref`.
14 /// ### Why is this bad?
15 /// This pattern has no effect in almost all cases.
17 /// ### Known problems
18 /// In some cases, `&ref` is needed to avoid a lifetime mismatch error.
21 /// fn foo(a: &Option<String>, b: &Option<String>) {
23 /// (None, &ref c) | (&ref c, None) => (),
24 /// (&Some(ref c), _) => (),
32 /// let mut v = Vec::<String>::new();
33 /// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
38 /// let mut v = Vec::<String>::new();
39 /// let _ = v.iter_mut().filter(|a| a.is_empty());
41 #[clippy::version = "pre 1.29.0"]
42 pub NEEDLESS_BORROWED_REFERENCE,
44 "destructuring a reference and borrowing the inner value"
47 declare_lint_pass!(NeedlessBorrowedRef => [NEEDLESS_BORROWED_REFERENCE]);
49 impl<'tcx> LateLintPass<'tcx> for NeedlessBorrowedRef {
50 fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
51 if pat.span.from_expansion() {
52 // OK, simple enough, lints doesn't check in macro.
57 // Only lint immutable refs, because `&mut ref T` may be useful.
58 if let PatKind::Ref(sub_pat, Mutability::Not) = pat.kind;
60 // Check sub_pat got a `ref` keyword (excluding `ref mut`).
61 if let PatKind::Binding(BindingAnnotation::Ref, .., spanned_name, _) = sub_pat.kind;
62 let parent_id = cx.tcx.hir().get_parent_node(pat.hir_id);
63 if let Some(parent_node) = cx.tcx.hir().find(parent_id);
65 // do not recurse within patterns, as they may have other references
66 // XXXManishearth we can relax this constraint if we only check patterns
67 // with a single ref pattern inside them
68 if let Node::Pat(_) = parent_node {
71 let mut applicability = Applicability::MachineApplicable;
72 span_lint_and_then(cx, NEEDLESS_BORROWED_REFERENCE, pat.span,
73 "this pattern takes a reference on something that is being de-referenced",
75 let hint = snippet_with_applicability(cx, spanned_name.span, "..", &mut applicability).into_owned();
78 "try removing the `&ref` part and just keep",