Revert "dart2js cps: Remove unneeded bailout on captured loop variables."

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
index fd3695ee1cc3882ffec3af0a59fb7214493eced3..5e224e25438c518d8e2f62451d016941f83e659f 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
@@ -2277,11 +2277,16 @@ abstract class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
 
 final String ABORT_IRNODE_BUILDER = "IrNode builder aborted";
 
-/// Determines which local variables should be boxed in a mutable variable
-/// inside a given try block.
-class TryBoxedVariables extends ast.Visitor {
+/// Classifies local variables and local functions as captured, if they
+/// are accessed from within a nested function.
+///
+/// This class is specific to the [DartIrBuilder], in that it gives up if it
+/// sees a feature that is currently unsupport by that builder. In particular,
+/// loop variables captured in a for-loop initializer, condition, or update
+/// expression are unsupported.
+class DartCapturedVariables extends ast.Visitor {
   final TreeElements elements;
-  TryBoxedVariables(this.elements);
+  DartCapturedVariables(this.elements);
 
   FunctionElement currentFunction;
   bool insideInitializer = false;
@@ -2327,6 +2332,25 @@ class TryBoxedVariables extends ast.Visitor {
     node.visitChildren(this);
   }
 
+  visitFor(ast.For node) {
+    if (node.initializer != null) visit(node.initializer);
+    if (node.condition != null) visit(node.condition);
+    if (node.update != null) visit(node.update);
+
+    // Give up if a variable was captured outside of the loop body.
+    if (node.initializer is ast.VariableDefinitions) {
+      ast.VariableDefinitions definitions = node.initializer;
+      for (ast.Node node in definitions.definitions.nodes) {
+        LocalElement loopVariable = elements[node];
+        if (capturedVariables.contains(loopVariable)) {
+          return giveup(node, 'For-loop variable captured in loop header');
+        }
+      }
+    }
+
+    if (node.body != null) visit(node.body);
+  }
+
   void handleSend(ast.Send node) {
     Element element = elements[node];
     if (Elements.isLocal(element) &&
@@ -2384,14 +2408,18 @@ class TryBoxedVariables extends ast.Visitor {
     if (currentFunction.asyncMarker != AsyncMarker.SYNC &&
         currentFunction.asyncMarker != AsyncMarker.SYNC_STAR &&
         currentFunction.asyncMarker != AsyncMarker.ASYNC) {
-      giveup(node, "cannot handle async* functions");
+      giveup(node, "cannot handle sync*/async* functions");
     }
 
+    bool savedInsideInitializer = insideInitializer;
     if (node.initializers != null) {
+      insideInitializer = true;
       visit(node.initializers);
     }
+    insideInitializer = false;
     visit(node.body);
     currentFunction = savedFunction;
+    insideInitializer = savedInsideInitializer;
   }
 
   visitTryStatement(ast.TryStatement node) {
@@ -3099,8 +3127,8 @@ class JsIrBuilderVisitor extends IrBuilderVisitor {
     return parameters;
   }
 
-  TryBoxedVariables _analyzeTryBoxedVariables(ast.Node node) {
-    TryBoxedVariables variables = new TryBoxedVariables(elements);
+  DartCapturedVariables _analyzeCapturedVariables(ast.Node node) {
+    DartCapturedVariables variables = new DartCapturedVariables(elements);
     try {
       variables.analyze(node);
     } catch (e) {
@@ -3130,7 +3158,7 @@ class JsIrBuilderVisitor extends IrBuilderVisitor {
     // error-prone.
     // TODO(kmillikin): We should combine closure conversion and try/catch
     // variable analysis in some way.
-    TryBoxedVariables variables = _analyzeTryBoxedVariables(node);
+    DartCapturedVariables variables = _analyzeCapturedVariables(node);
     tryStatements = variables.tryStatements;
     IrBuilder builder = getBuilderFor(body);
 
@@ -3155,7 +3183,7 @@ class JsIrBuilderVisitor extends IrBuilderVisitor {
             element,
             node,
             elements);
-    TryBoxedVariables variables = _analyzeTryBoxedVariables(node);
+    DartCapturedVariables variables = _analyzeCapturedVariables(node);
     tryStatements = variables.tryStatements;
     IrBuilder builder = getBuilderFor(element);
     return withBuilder(builder, () => _makeFunctionBody(element, node));