-//! Checks for useless borrowed references.
-//!
-//! This lint is **warn** by default
-
use crate::utils::{snippet_with_applicability, span_lint_and_then};
use if_chain::if_chain;
-use rustc::declare_lint_pass;
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc_errors::Applicability;
use rustc_hir::{BindingAnnotation, Mutability, Node, Pat, PatKind};
-use rustc_session::declare_tool_lint;
+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.
- ///
- /// **Why is this bad?** It is mostly useless and make the code look more
- /// complex than it
- /// actually is.
+ /// **What it does:** Checks for bindings that destructure a reference and borrow the inner
+ /// value with `&ref`.
///
- /// **Known problems:** It seems that the `&ref` pattern is sometimes useful.
- /// For instance in the following snippet:
- /// ```rust,ignore
- /// enum Animal {
- /// Cat(u64),
- /// Dog(u64),
- /// }
+ /// **Why is this bad?** This pattern has no effect in almost all cases.
///
- /// fn foo(a: &Animal, b: &Animal) {
+ /// **Known problems:** In some cases, `&ref` is needed to avoid a lifetime mismatch error.
+ /// Example:
+ /// ```rust
+ /// 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"
}
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<'_>) {
+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;
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| {
+ |diag| {
let hint = snippet_with_applicability(cx, spanned_name.span, "..", &mut applicability).into_owned();
- db.span_suggestion(
+ diag.span_suggestion(
pat.span,
"try removing the `&ref` part and just keep",
hint,