modify code

[rust.git] / clippy_lints / src / needless_borrowed_ref.rs

diff --git a/clippy_lints/src/needless_borrowed_ref.rs b/clippy_lints/src/needless_borrowed_ref.rs
index 497ce3c292714675f26bbf9d428e3299b92d6e8c..0fcc419e722272b3afccf433f60f3afb07974436 100644 (file)
--- a/clippy_lints/src/needless_borrowed_ref.rs
+++ b/clippy_lints/src/needless_borrowed_ref.rs
@@ -1,59 +1,53 @@
-//! Checks for useless borrowed references.
-//!
-//! This lint is **warn** by default
-
-use crate::utils::{snippet_with_applicability, span_lint_and_then};
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::source::snippet_with_applicability;
 use if_chain::if_chain;
-use rustc::lint::{LateContext, LateLintPass};
 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.
-    ///
-    /// **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:**
+    /// ### 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());
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
     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;
@@ -61,7 +55,7 @@ fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat<'_>) {
 
         if_chain! {
             // Only lint immutable refs, because `&mut ref T` may be useful.
-            if let PatKind::Ref(ref sub_pat, Mutability::Not) = pat.kind;
+            if let PatKind::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.kind;
@@ -77,9 +71,9 @@ fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat<'_>) {
                 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,