ExitDetector: Examine continue when determining a 'do'

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 33dc56e933bfaa1926d071f466bb3efd263c306d..eb2fb9dc384a67d79f698c150a56134aaf46873d 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -3499,6 +3499,12 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
   bool _enclosingBlockContainsBreak = false;
 
   /**
+   * Set to `true` when a `continue` is encountered, and reset to `false` when a
+   * `do`, `while`, `for` or `switch` block is entered.
+   */
+  bool _enclosingBlockContainsContinue = false;
+
+  /**
    * Add node when a labelled `break` is encountered.
    */
   Set<AstNode> _enclosingBlockBreaksLabel = new Set<AstNode>();
@@ -3606,14 +3612,24 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
   }
 
   @override
-  bool visitContinueStatement(ContinueStatement node) => false;
+  bool visitContinueStatement(ContinueStatement node) {
+    _enclosingBlockContainsContinue = true;

[Brian Wilkerson, 2016/06/28 20:47:33]

This is ignoring the presence or absence of a label. It seems like the condition
should apply to enclosing loops if the label is associated with that loop and
not just be discarded when we exit the current loop, such as:

foo: while (...) {
  while (...) {
    continue foo;
  }
}

but maybe it doesn't matter.

Also, I noticed that you deleted the visitSwitchCase (or Statement) code, but
the spec says:

Let sc be a continue statement. If sc is of the form continue L;, then let sE
be the the innermost labeled do (17.8), for (17.6) or while (17.7) statement or
case clause with label L enclosing sc.

Notice the last line: if the continue has a label it can apply to a case clause.
Not sure how that ought to affect the logic here, but some test cases are in
order.

+    return false;
+  }
 
   @override
   bool visitDoStatement(DoStatement node) {
     bool outerBreakValue = _enclosingBlockContainsBreak;
+    bool outerContinueValue = _enclosingBlockContainsContinue;
     _enclosingBlockContainsBreak = false;
+    _enclosingBlockContainsContinue = false;
     try {
-      if (_nodeExits(node.body) && !_enclosingBlockContainsBreak) {
+      bool bodyExits = _nodeExits(node.body);
+      bool containsBreakOrContinue =
+          _enclosingBlockContainsBreak || _enclosingBlockContainsContinue;
+      // Even if we determine that the body "exits", there might be break or
+      // continue statements that actually mean it _doesn't_ always exit.
+      if (bodyExits && !containsBreakOrContinue) {
         return true;
       }
       Expression conditionExpression = node.condition;
@@ -3630,6 +3646,7 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
       return false;
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
+      _enclosingBlockContainsContinue = outerContinueValue;
     }
   }
 
@@ -3643,18 +3660,23 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
   @override
   bool visitForEachStatement(ForEachStatement node) {
     bool outerBreakValue = _enclosingBlockContainsBreak;
+    bool outerContinueValue = _enclosingBlockContainsContinue;
     _enclosingBlockContainsBreak = false;
+    _enclosingBlockContainsContinue = false;
     try {
       return _nodeExits(node.iterable);
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
+      _enclosingBlockContainsContinue = outerContinueValue;
     }
   }
 
   @override
   bool visitForStatement(ForStatement node) {
     bool outerBreakValue = _enclosingBlockContainsBreak;
+    bool outerContinueValue = _enclosingBlockContainsContinue;
     _enclosingBlockContainsBreak = false;
+    _enclosingBlockContainsContinue = false;
     try {
       if (node.variables != null &&
           _visitVariableDeclarations(node.variables.variables)) {
@@ -3684,6 +3706,7 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
       return false;
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
+      _enclosingBlockContainsContinue = outerContinueValue;
     }
   }
 
@@ -3909,7 +3932,9 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
   @override
   bool visitWhileStatement(WhileStatement node) {
     bool outerBreakValue = _enclosingBlockContainsBreak;
+    bool outerContinueValue = _enclosingBlockContainsContinue;
     _enclosingBlockContainsBreak = false;
+    _enclosingBlockContainsContinue = false;
     try {
       Expression conditionExpression = node.condition;
       if (conditionExpression.accept(this)) {
@@ -3936,6 +3961,7 @@ class ExitDetector extends GeneralizingAstVisitor<bool> {
       return false;
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
+      _enclosingBlockContainsContinue = outerContinueValue;
     }
   }