ExitDetector: Examine continue when determining a 'do'

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 3481 matching lines @@
  * expression, or simple infinite loop such as `while(true)`.
  */
 class ExitDetector extends GeneralizingAstVisitor<bool> {
   /**
    * Set to `true` when a `break` is encountered, and reset to `false` when a
    * `do`, `while`, `for` or `switch` block is entered.
    */
   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>();
 
   @override
   bool visitArgumentList(ArgumentList node) =>
       _visitExpressions(node.arguments);
 
   @override
   bool visitAsExpression(AsExpression node) => _nodeExits(node.expression);
@@ skipping 87 matching lines @@
     if (_nodeExits(conditionExpression)) {
       return true;
     }
     if (thenStatement == null || elseStatement == null) {
       return false;
     }
     return thenStatement.accept(this) && elseStatement.accept(this);
   }
 
   @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;
       if (_nodeExits(conditionExpression)) {
         return true;
       }
       // TODO(jwren) Do we want to take all constant expressions into account?
       if (conditionExpression is BooleanLiteral) {
         // If do {} while (true), and the body doesn't break, then return true.
         if (conditionExpression.value && !_enclosingBlockContainsBreak) {
           return true;
         }
       }
       return false;
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
+      _enclosingBlockContainsContinue = outerContinueValue;
     }
   }
 
   @override
   bool visitEmptyStatement(EmptyStatement node) => false;
 
   @override
   bool visitExpressionStatement(ExpressionStatement node) =>
       _nodeExits(node.expression);
 
   @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)) {
         return true;
       }
       if (node.initialization != null && _nodeExits(node.initialization)) {
         return true;
       }
       Expression conditionExpression = node.condition;
       if (conditionExpression != null && _nodeExits(conditionExpression)) {
         return true;
       }
       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) {
         if (blockReturns || !_enclosingBlockContainsBreak) {
           return true;
         }
       }
       return false;
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
+      _enclosingBlockContainsContinue = outerContinueValue;
     }
   }
 
   @override
   bool visitFunctionDeclarationStatement(FunctionDeclarationStatement node) =>
       false;
 
   @override
   bool visitFunctionExpression(FunctionExpression node) => false;
 
@@ skipping 205 matching lines @@
       if (variables[i].accept(this)) {
         return true;
       }
     }
     return false;
   }
 
   @override
   bool visitWhileStatement(WhileStatement node) {
     bool outerBreakValue = _enclosingBlockContainsBreak;
+    bool outerContinueValue = _enclosingBlockContainsContinue;
     _enclosingBlockContainsBreak = false;
+    _enclosingBlockContainsContinue = false;
     try {
       Expression conditionExpression = node.condition;
       if (conditionExpression.accept(this)) {
         return true;
       }
       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 have a break, then return true.
         // The body might be found to exit, but if there are any break
         // statements, then it is a faulty finding. In other words:
         //
         // * If the body exits, and does not contain a break statement, then
         //   it exits.
         // * If the body does not exit, and does not contain a break statement,
         //   then it loops infinitely (also an exit).
         //
         // As both conditions forbid any break statements to be found, the logic
         // just boils down to checking [_enclosingBlockContainsBreak].
         if (conditionExpression.value && !_enclosingBlockContainsBreak) {
           return true;
         }
       }
       return false;
     } finally {
       _enclosingBlockContainsBreak = outerBreakValue;
+      _enclosingBlockContainsContinue = outerContinueValue;
     }
   }
 
   @override
   bool visitYieldStatement(YieldStatement node) => _nodeExits(node.expression);
 
   /**
    * Return `true` if the given node exits.
    *
    * @param node the node being tested
@@ skipping 7091 matching lines @@
       return null;
     }
     if (identical(node.staticElement, variable)) {
       if (node.inSetterContext()) {
         result = true;
       }
     }
     return null;
   }
 }