Merge pull request #2056 from topecongiro/issue-1851

Add suggestion to needless_borrow

Author: llogiq

clippy_lints/src/needless_borrow.rs

@@ -6,7 +6,7 @@ use rustc::lint::*;
 use rustc::hir::{BindingAnnotation, Expr, ExprAddrOf, MutImmutable, Pat, PatKind};
 use rustc::ty;
 use rustc::ty::adjustment::{Adjust, Adjustment};
-use utils::{in_macro, span_lint};
+use utils::{in_macro, snippet_opt, span_lint_and_then};
 
 /// **What it does:** Checks for address of operations (`&`) that are going to
 /// be dereferenced immediately by the compiler.
@@ -54,12 +54,17 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrow {
                         ..
                     }] = *adj3
                     {
-                        span_lint(
+                        span_lint_and_then(
                             cx,
                             NEEDLESS_BORROW,
                             e.span,
-                            "this expression borrows a reference that is immediately dereferenced by the \
-                             compiler",
+                            "this expression borrows a reference that is immediately dereferenced \
+                             by the compiler",
+                            |db| {
+                                if let Some(snippet) = snippet_opt(cx, inner.span) {
+                                    db.span_suggestion(e.span, "change this to", snippet);
+                                }
+                            }
                         );
                     }
                 }
@@ -71,14 +76,24 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrow {
             return;
         }
         if_let_chain! {[
-            let PatKind::Binding(BindingAnnotation::Ref, _, _, _) = pat.node,
+            let PatKind::Binding(BindingAnnotation::Ref, _, name, _) = pat.node,
             let ty::TyRef(_, ref tam) = cx.tables.pat_ty(pat).sty,
             tam.mutbl == MutImmutable,
             let ty::TyRef(_, ref tam) = tam.ty.sty,
             // only lint immutable refs, because borrowed `&mut T` cannot be moved out
             tam.mutbl == MutImmutable,
         ], {
-            span_lint(cx, NEEDLESS_BORROW, pat.span, "this pattern creates a reference to a reference")
+            span_lint_and_then(
+                cx,
+                NEEDLESS_BORROW,
+                pat.span,
+                "this pattern creates a reference to a reference",
+                |db| {
+                    if let Some(snippet) = snippet_opt(cx, name.span) {
+                        db.span_suggestion(pat.span, "change this to", snippet);
+                    }
+                }
+            )
         }}
     }
 }

tests/ui/eta.stderr

@@ -22,7 +22,7 @@ error: this expression borrows a reference that is immediately dereferenced by t
   --> $DIR/eta.rs:11:21
    |
 11 |     all(&[1, 2, 3], &&2, |x, y| below(x, y)); //is adjusted
-   |                     ^^^
+   |                     ^^^ help: change this to: `&2`
    |
    = note: `-D needless-borrow` implied by `-D warnings`
 

tests/ui/needless_borrow.stderr

@@ -2,21 +2,21 @@ error: this expression borrows a reference that is immediately dereferenced by t
   --> $DIR/needless_borrow.rs:13:15
    |
 13 |     let c = x(&&a);
-   |               ^^^
+   |               ^^^ help: change this to: `&a`
    |
    = note: `-D needless-borrow` implied by `-D warnings`
 
 error: this pattern creates a reference to a reference
   --> $DIR/needless_borrow.rs:20:17
    |
 20 |     if let Some(ref cake) = Some(&5) {}
-   |                 ^^^^^^^^
+   |                 ^^^^^^^^ help: change this to: `cake`
 
 error: this expression borrows a reference that is immediately dereferenced by the compiler
   --> $DIR/needless_borrow.rs:27:15
    |
 27 |         46 => &&a,
-   |               ^^^
+   |               ^^^ help: change this to: `&a`
 
 error: this pattern takes a reference on something that is being de-referenced
   --> $DIR/needless_borrow.rs:49:34
@@ -36,7 +36,7 @@ error: this pattern creates a reference to a reference
   --> $DIR/needless_borrow.rs:50:31
    |
 50 |     let _ = v.iter().filter(|&ref a| a.is_empty());
-   |                               ^^^^^
+   |                               ^^^^^ help: change this to: `a`
 
 error: aborting due to 6 previous errors