Add label support to ExitDetector

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

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index 7dbf6e42c99492dbe9054a776fd77d0869c52b5e..f1fb45e006db2ecb53a565d47a312a0f6fdb6b50 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -3470,6 +3470,11 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
    */
   bool _enclosingBlockContainsBreak = false;
 
+  /**
+   * Add node when a labelled `break` is encountered.
+   */
+  Set<AstNode> _enclosingBlockBreaksLabel = new Set<AstNode>();
+
   @override
   bool visitArgumentList(ArgumentList node) =>
       _visitExpressions(node.arguments);
@@ -3545,6 +3550,9 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
   @override
   bool visitBreakStatement(BreakStatement node) {
     _enclosingBlockContainsBreak = true;
+    if (node.label != null) {
+      _enclosingBlockBreaksLabel.add(node.target);
+    }
     return false;
   }
 
@@ -3634,13 +3642,13 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
       if (_visitExpressions(node.updaters)) {
         return true;
       }
+      bool blockReturns = _nodeExits(node.body);
       // TODO(jwren) Do we want to take all constant expressions into account?
       // If for(; true; ) (or for(;;)), and the body doesn't return or the body
       // doesn't have a break, then return true.
       bool implicitOrExplictTrue = conditionExpression == null ||
           (conditionExpression is BooleanLiteral && conditionExpression.value);
       if (implicitOrExplictTrue) {
-        bool blockReturns = _nodeExits(node.body);
         if (blockReturns || !_enclosingBlockContainsBreak) {
           return true;
         }
@@ -3680,18 +3688,18 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
     // TODO(jwren) Do we want to take all constant expressions into account?
     if (conditionExpression is BooleanLiteral) {
       if (conditionExpression.value) {
-        // if(true) ...
+        // if (true) ...
         return _nodeExits(thenStatement);
       } else if (elseStatement != null) {
         // if (false) ...
         return _nodeExits(elseStatement);
       }
     }
-    if (thenStatement == null || elseStatement == null) {
-      return false;
-    }
     bool thenExits = _nodeExits(thenStatement);
     bool elseExits = _nodeExits(elseStatement);
+    if (thenStatement == null || elseStatement == null) {
+      return false;
+    }
     return thenExits && elseExits;
   }
 
@@ -3718,8 +3726,16 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
   bool visitLabel(Label node) => false;
 
   @override
-  bool visitLabeledStatement(LabeledStatement node) =>
-      node.statement.accept(this);
+  bool visitLabeledStatement(LabeledStatement node) {
+    try {
+      bool statementExits = _nodeExits(node.statement);
+      bool neverBrokeFromLabel =
+          !_enclosingBlockBreaksLabel.contains(node.statement);
+      return statementExits && neverBrokeFromLabel;
+    } finally {
+      _enclosingBlockBreaksLabel.remove(node.statement);
+    }
+  }
 
   @override
   bool visitLiteral(Literal node) => false;
@@ -3873,11 +3889,11 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
       if (conditionExpression.accept(this)) {
         return true;
       }
+      bool blockReturns = node.body.accept(this);
       // TODO(jwren) Do we want to take all constant expressions into account?
       if (conditionExpression is BooleanLiteral) {
         // If while(true), and the body doesn't return or the body doesn't have
         // a break, then return true.
-        bool blockReturns = node.body.accept(this);
         if (conditionExpression.value &&
             (blockReturns || !_enclosingBlockContainsBreak)) {
           return true;
@@ -3912,7 +3928,7 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
   }
 
   bool _visitStatements(NodeList<Statement> statements) {
-    for (int i = statements.length - 1; i >= 0; i--) {
+    for (int i = 0; i < statements.length; i++) {
       if (statements[i].accept(this)) {
         return true;
       }