Disable closures in initializers and fail instead of crashing.

frog/leg/ssa/builder.dart

 // Copyright (c) 2012, 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.
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
   SourceString mapOperatorToMethodName(Operator op) {
     String name = op.source.stringValue;
@@ skipping 1221 matching lines @@
 
     conditionBlock.addSuccessor(loopEntryBlock);  // The back-edge.
     loopEntryBlock.postProcessLoopHeader();
 
     endLoop(loopEntryBlock, conditionBlock, jumpHandler, localsHandler);
     jumpHandler.close();
   }
 
   visitFunctionExpression(FunctionExpression node) {
     ClosureData nestedClosureData = closureDataCache[node];
+    if (nestedClosureData === null) {
+      // TODO(floitsch): we can only assume that the reason for not having a
+      // closure data here is, because the function is inside an initializer.
+      compiler.unimplemented("Closures inside initializers", node: node);
+    }
     assert(nestedClosureData !== null);
     assert(nestedClosureData.closureClassElement !== null);
     ClassElement closureClassElement =
         nestedClosureData.closureClassElement;
     FunctionElement callElement = nestedClosureData.callElement;
     compiler.enqueue(new WorkItem.toCodegen(callElement, elements));
     compiler.registerInstantiatedClass(closureClassElement);
     assert(closureClassElement.members.isEmpty());
 
     List<HInstruction> capturedVariables = <HInstruction>[];
@@ skipping 1553 matching lines @@
     HInstruction concat = new HAdd(target, left, right);
     builder.add(concat);
     return concat;
   }
 
   HInstruction result() {
     flushAccumulator();
     return prefix;
   }
 }