ExitDetector: Don't short-circuit return on non-exiting case statements

pkg/analyzer/lib/src/generated/resolver.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.generated.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 3737 matching lines @@
   @override
   bool visitSwitchDefault(SwitchDefault node) =>
       _visitStatements(node.statements);
 
   @override
   bool visitSwitchStatement(SwitchStatement node) {
     bool outerBreakValue = _enclosingBlockContainsBreak;
     _enclosingBlockContainsBreak = false;
     try {
       bool hasDefault = false;
+      bool hasNonExitingCase = false;
       List<SwitchMember> members = node.members;
       for (int i = 0; i < members.length; i++) {
         SwitchMember switchMember = members[i];
         if (switchMember is SwitchDefault) {
           hasDefault = true;
-          // If this is the last member and there are no statements, return
-          // false
+          // If this is the last member and there are no statements, then it
+          // does not exit.
           if (switchMember.statements.isEmpty && i + 1 == members.length) {
-            return false;
+            hasNonExitingCase = true;
+            continue;
           }
         }
-        // For switch members with no statements, don't visit the children,
-        // otherwise, return false if no return is found in the children
-        // statements.
+        // For switch members with no statements, don't visit the children.
+        // Otherwise, if there children statements don't exit, mark this as a
+        // non-exiting case.
         if (!switchMember.statements.isEmpty && !switchMember.accept(this)) {
-          return false;
+          hasNonExitingCase = true;
         }
       }
+      if (hasNonExitingCase) {
+        return false;
+      }
       // As all cases exit, return whether that list includes `default`.
       return hasDefault;
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
     }
   }
 
   @override
   bool visitThisExpression(ThisExpression node) => false;
 
@@ skipping 7156 matching lines @@
       return null;
     }
     if (identical(node.staticElement, variable)) {
       if (node.inSetterContext()) {
         result = true;
       }
     }
     return null;
   }
 }