Fix match_same_arms to fail late

Changes:
- Add a function search_same_list which return a list of matched expressions
- Change the match_same_arms implementation behaviour. It will lint each same arms found.

clippy_lints/src/copies.rs

@@ -185,7 +185,10 @@ fn lint_match_arms(cx: &LateContext<'_, '_>, expr: &Expr) {
         };
 
         let indexed_arms: Vec<(usize, &Arm)> = arms.iter().enumerate().collect();
-        if let Some((&(_, i), &(_, j))) = search_same(&indexed_arms, hash, eq) {
+        search_same_list(&indexed_arms, hash, eq).map(|item| {
+            for match_expr in item {
+                let (&(_, i), &(_, j)) = match_expr;
+
                 span_lint_and_then(
                     cx,
                     MATCH_SAME_ARMS,
@@ -223,6 +226,7 @@ fn lint_match_arms(cx: &LateContext<'_, '_>, expr: &Expr) {
                     },
                 );
             }
+        });
     }
 }
 
@@ -360,3 +364,36 @@ where
 
     None
 }
+
+fn search_same_list<T, Hash, Eq>(exprs: &[T], hash: Hash, eq: Eq) -> Option<Vec<(&T, &T)>>
+where
+    Hash: Fn(&T) -> u64,
+    Eq: Fn(&T, &T) -> bool,
+{
+    let mut match_expr_list: Vec<(&T, &T)> = Vec::new();
+
+    let mut map: FxHashMap<_, Vec<&_>> =
+        FxHashMap::with_capacity_and_hasher(exprs.len(), BuildHasherDefault::default());
+
+    for expr in exprs {
+        match map.entry(hash(expr)) {
+            Entry::Occupied(mut o) => {
+                for o in o.get() {
+                    if eq(o, expr) {
+                        match_expr_list.push((o, expr));
+                    }
+                }
+                o.get_mut().push(expr);
+            },
+            Entry::Vacant(v) => {
+                v.insert(vec![expr]);
+            },
+        }
+    }
+
+    if match_expr_list.is_empty() {
+        None
+    } else {
+        Some(match_expr_list)
+    }
+}