From 7580da306e338089b1cffedb09a71cb11debddf5 Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Fri, 21 Aug 2015 20:49:59 +0200
Subject: [PATCH] matches: special message for this case

match &e { &Pat1 => {}, &Pat2 => {}, ... }

(inspired by dogfood fixes)
---
 src/matches.rs                | 27 ++++++++++++++-------------
 tests/compile-fail/matches.rs |  6 ++++++
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/src/matches.rs b/src/matches.rs
index b704a2b47bbc..002da07f50b7 100644
--- a/src/matches.rs
+++ b/src/matches.rs
@@ -55,9 +55,15 @@ impl LintPass for MatchPass {
 
             // check preconditions for MATCH_REF_PATS
             if has_only_ref_pats(arms) {
-                span_lint(cx, MATCH_REF_PATS, expr.span, &format!(
-                    "instead of prefixing all patterns with `&`, you can dereference the \
-                     expression to match: `match *{} {{ ...`", snippet(cx, ex.span, "..")));
+                if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
+                    span_lint(cx, MATCH_REF_PATS, expr.span, &format!(
+                        "you don't need to add `&` to both the expression to match \
+                         and the patterns: use `match {} {{ ...`", snippet(cx, inner.span, "..")));
+                } else {
+                    span_lint(cx, MATCH_REF_PATS, expr.span, &format!(
+                        "instead of prefixing all patterns with `&`, you can dereference the \
+                         expression to match: `match *{} {{ ...`", snippet(cx, ex.span, "..")));
+                }
             }
         }
     }
@@ -72,14 +78,9 @@ fn is_unit_expr(expr: &Expr) -> bool {
 }
 
 fn has_only_ref_pats(arms: &[Arm]) -> bool {
-    for arm in arms {
-        for pat in &arm.pats {
-            match pat.node {
-                PatRegion(..) => (),  // &-patterns
-                PatWild(..) => (),    // an "anything" wildcard is also fine
-                _ => return false,
-            }
-        }
-    }
-    true
+    arms.iter().flat_map(|a| &a.pats).all(|p| match p.node {
+        PatRegion(..) => true,  // &-patterns
+        PatWild(..) => true,    // an "anything" wildcard is also fine
+        _ => false,
+    })
 }
diff --git a/tests/compile-fail/matches.rs b/tests/compile-fail/matches.rs
index 43cf43b68df5..3cc540992c99 100755
--- a/tests/compile-fail/matches.rs
+++ b/tests/compile-fail/matches.rs
@@ -53,6 +53,12 @@ fn ref_pats() {
         &(v, 1) => println!("{}", v),
         _ => println!("none"),
     }
+    // special case: using & both in expr and pats
+    let w = Some(0);
+    match &w {  //~ERROR you don't need to add `&` to both
+        &Some(v) => println!("{:?}", v),
+        &None => println!("none"),
+    }
 }
 
 fn main() {