fixes #259, clone ast before mutation

lib/src/codegen/reify_coercions.dart

 // Copyright (c) 2015, 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 dev_compiler.src.codegen.reify_coercions;
 
 import 'package:analyzer/analyzer.dart' as analyzer;
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:logging/logging.dart' as logger;
@@ skipping 93 matching lines @@
     var cm = new CoercionManager(vm, tm);
     var inferrer = new _Inference(compiler.rules, tm);
     return new CoercionReifier._(cm, tm, vm, library, inferrer);
   }
 
   // This should be the entry point for this class.  Entering via the
   // visit functions directly may not do the right thing with respect
   // to discharging the collected definitions.
   // Returns the set of new type identifiers added by the reifier
   Map<Identifier, NewTypeIdDesc> reify() {
-    _library.partsThenLibrary.forEach(generateUnit);
+    _library.partsThenLibrary.forEach(visitCompilationUnit);
     return _tm.addedTypes;
   }
 
-  void generateUnit(CompilationUnit unit) {
-    visitCompilationUnit(unit);
-  }
-
   @override
   Object visitExpression(Expression node) {
     var info = CoercionInfo.get(node);
     if (info is InferredTypeBase) {
-      return _visitInferredTypeBase(info);
+      return _visitInferredTypeBase(info, node);
     } else if (info is DownCast) {
-      return _visitDownCast(info);
+      return _visitDownCast(info, node);
     }
     return super.visitExpression(node);
   }
 
   ///////////////// Private //////////////////////////////////
 
-  Object _visitInferredTypeBase(InferredTypeBase node) {
-    var expr = node.node;
+  Object _visitInferredTypeBase(InferredTypeBase node, Expression expr) {
     var success = _inferrer.inferExpression(expr, node.type, <String>[]);
     assert(success);
     expr.visitChildren(this);
     return null;
   }
 
-  Object _visitDownCast(DownCast node) {
-    var expr = node.node;
+  Object _visitDownCast(DownCast node, Expression expr) {
     var parent = expr.parent;
     expr.visitChildren(this);
     Expression newE = _cm.coerceExpression(expr, node.cast);
     if (!identical(expr, newE)) {
       var replaced = parent.accept(new NodeReplacer(expr, newE));
       // It looks like NodeReplacer will always return true.
       // It does throw IllegalArgumentException though, if child is not found.
       assert(replaced);
     }
     return null;
@@ skipping 343 matching lines @@
     var t = _mkNewTypeName(dType, id, args);
     return t;
   }
 
   TypeName _mkNewTypeName(DartType type, Identifier id, List<TypeName> args) {
     var t = AstBuilder.typeName(id, args);
     t.type = type;
     return t;
   }
 }