-//! Checks for useless borrowed references.
-//!
-//! This lint is **warn** by default
-
-use crate::utils::{in_macro, snippet, span_lint_and_then};
+use crate::utils::{snippet_with_applicability, span_lint_and_then};
use if_chain::if_chain;
-use rustc::hir::{BindingAnnotation, MutImmutable, Pat, PatKind};
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
-use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
+use rustc_hir::{BindingAnnotation, Mutability, Node, Pat, PatKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
- /// **What it does:** Checks for useless borrowed references.
+ /// **What it does:** Checks for bindings that destructure a reference and borrow the inner
+ /// value with `&ref`.
///
- /// **Why is this bad?** It is mostly useless and make the code look more
- /// complex than it
- /// actually is.
+ /// **Why is this bad?** This pattern has no effect in almost all cases.
///
- /// **Known problems:** It seems that the `&ref` pattern is sometimes useful.
- /// For instance in the following snippet:
+ /// **Known problems:** In some cases, `&ref` is needed to avoid a lifetime mismatch error.
+ /// Example:
/// ```rust
- /// enum Animal {
- /// Cat(u64),
- /// Dog(u64),
- /// }
- ///
- /// fn foo(a: &Animal, b: &Animal) {
+ /// fn foo(a: &Option<String>, b: &Option<String>) {
/// match (a, b) {
- /// (&Animal::Cat(v), k) | (k, &Animal::Cat(v)) => (), // lifetime
- /// mismatch error
- /// (&Animal::Dog(ref c), &Animal::Dog(_)) => ()
- /// }
+ /// (None, &ref c) | (&ref c, None) => (),
+ /// (&Some(ref c), _) => (),
+ /// };
/// }
/// ```
- /// There is a lifetime mismatch error for `k` (indeed a and b have distinct
- /// lifetime).
- /// This can be fixed by using the `&ref` pattern.
- /// However, the code can also be fixed by much cleaner ways
///
/// **Example:**
+ /// Bad:
/// ```rust
/// let mut v = Vec::<String>::new();
/// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
/// ```
- /// This closure takes a reference on something that has been matched as a
- /// reference and
- /// de-referenced.
- /// As such, it could just be |a| a.is_empty()
+ ///
+ /// Good:
+ /// ```rust
+ /// let mut v = Vec::<String>::new();
+ /// let _ = v.iter_mut().filter(|a| a.is_empty());
+ /// ```
pub NEEDLESS_BORROWED_REFERENCE,
complexity,
- "taking a needless borrowed reference"
+ "destructuring a reference and borrowing the inner value"
}
-#[derive(Copy, Clone)]
-pub struct NeedlessBorrowedRef;
-
-impl LintPass for NeedlessBorrowedRef {
- fn get_lints(&self) -> LintArray {
- lint_array!(NEEDLESS_BORROWED_REFERENCE)
- }
-
- fn name(&self) -> &'static str {
- "NeedlessBorrowedRef"
- }
-}
+declare_lint_pass!(NeedlessBorrowedRef => [NEEDLESS_BORROWED_REFERENCE]);
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrowedRef {
- fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
- if in_macro(pat.span) {
+impl<'tcx> LateLintPass<'tcx> for NeedlessBorrowedRef {
+ fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
+ if pat.span.from_expansion() {
// OK, simple enough, lints doesn't check in macro.
return;
}
if_chain! {
// Only lint immutable refs, because `&mut ref T` may be useful.
- if let PatKind::Ref(ref sub_pat, MutImmutable) = pat.node;
+ if let PatKind::Ref(ref sub_pat, Mutability::Not) = pat.kind;
// Check sub_pat got a `ref` keyword (excluding `ref mut`).
- if let PatKind::Binding(BindingAnnotation::Ref, .., spanned_name, _) = sub_pat.node;
+ if let PatKind::Binding(BindingAnnotation::Ref, .., spanned_name, _) = sub_pat.kind;
+ let parent_id = cx.tcx.hir().get_parent_node(pat.hir_id);
+ if let Some(parent_node) = cx.tcx.hir().find(parent_id);
then {
+ // do not recurse within patterns, as they may have other references
+ // XXXManishearth we can relax this constraint if we only check patterns
+ // with a single ref pattern inside them
+ if let Node::Pat(_) = parent_node {
+ return;
+ }
+ let mut applicability = Applicability::MachineApplicable;
span_lint_and_then(cx, NEEDLESS_BORROWED_REFERENCE, pat.span,
"this pattern takes a reference on something that is being de-referenced",
- |db| {
- let hint = snippet(cx, spanned_name.span, "..").into_owned();
- db.span_suggestion(
+ |diag| {
+ let hint = snippet_with_applicability(cx, spanned_name.span, "..", &mut applicability).into_owned();
+ diag.span_suggestion(
pat.span,
"try removing the `&ref` part and just keep",
hint,
- Applicability::MachineApplicable, // snippet
+ applicability,
);
});
}