86 lines
3.3 KiB
Rust
86 lines
3.3 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet_with_applicability;
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::{BindingAnnotation, Mutability, Node, Pat, PatKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for bindings that destructure a reference and borrow the inner
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/// value with `&ref`.
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///
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/// ### Why is this bad?
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/// This pattern has no effect in almost all cases.
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///
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/// ### Known problems
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/// In some cases, `&ref` is needed to avoid a lifetime mismatch error.
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/// Example:
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/// ```rust
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/// fn foo(a: &Option<String>, b: &Option<String>) {
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/// match (a, b) {
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/// (None, &ref c) | (&ref c, None) => (),
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/// (&Some(ref c), _) => (),
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/// };
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/// }
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/// ```
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///
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/// ### Example
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/// Bad:
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/// ```rust
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/// let mut v = Vec::<String>::new();
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/// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
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/// ```
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///
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/// Good:
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/// ```rust
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/// let mut v = Vec::<String>::new();
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/// let _ = v.iter_mut().filter(|a| a.is_empty());
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/// ```
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pub NEEDLESS_BORROWED_REFERENCE,
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complexity,
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"destructuring a reference and borrowing the inner value"
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}
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declare_lint_pass!(NeedlessBorrowedRef => [NEEDLESS_BORROWED_REFERENCE]);
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impl<'tcx> LateLintPass<'tcx> for NeedlessBorrowedRef {
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fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
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if pat.span.from_expansion() {
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// OK, simple enough, lints doesn't check in macro.
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return;
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}
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if_chain! {
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// Only lint immutable refs, because `&mut ref T` may be useful.
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if let PatKind::Ref(sub_pat, Mutability::Not) = pat.kind;
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// Check sub_pat got a `ref` keyword (excluding `ref mut`).
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if let PatKind::Binding(BindingAnnotation::Ref, .., spanned_name, _) = sub_pat.kind;
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let parent_id = cx.tcx.hir().get_parent_node(pat.hir_id);
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if let Some(parent_node) = cx.tcx.hir().find(parent_id);
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then {
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// do not recurse within patterns, as they may have other references
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// XXXManishearth we can relax this constraint if we only check patterns
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// with a single ref pattern inside them
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if let Node::Pat(_) = parent_node {
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return;
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}
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let mut applicability = Applicability::MachineApplicable;
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span_lint_and_then(cx, NEEDLESS_BORROWED_REFERENCE, pat.span,
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"this pattern takes a reference on something that is being de-referenced",
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|diag| {
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let hint = snippet_with_applicability(cx, spanned_name.span, "..", &mut applicability).into_owned();
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diag.span_suggestion(
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pat.span,
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"try removing the `&ref` part and just keep",
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hint,
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applicability,
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);
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});
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}
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}
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}
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}
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