Implement new flatten specification.

pkg/compiler/lib/src/typechecker.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.
 
 part of dart2js;
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name => "Type checker";
 
@@ skipping 1572 matching lines @@
 
     // Executing a return statement return e; [...] It is a static type warning
     // if the type of e may not be assigned to the declared return type of the
     // immediately enclosing function.
     if (expression != null) {
       DartType expressionType = analyze(expression);
       if (executableContext.isGenerativeConstructor) {
         // The resolver already emitted an error for this expression.
       } else {
         if (currentAsyncMarker == AsyncMarker.ASYNC) {
-          expressionType = coreTypes.futureType(flatten(expressionType));
+          expressionType = coreTypes.futureType(types.flatten(expressionType));
         }
         if (expectedReturnType.isVoid &&
             !types.isAssignable(expressionType, const VoidType())) {
           reportTypeWarning(expression, MessageKind.RETURN_VALUE_IN_VOID);
         } else {
           checkAssignable(expression, expressionType, expectedReturnType);
         }
       }
 
     } else if (!types.isAssignable(expectedReturnType, const VoidType())) {
       // Let f be the function immediately enclosing a return statement of the
       // form 'return;' It is a static warning if both of the following
       // conditions hold:
       // - f is not a generative constructor.
       // - The return type of f may not be assigned to void.
       reportTypeWarning(node, MessageKind.RETURN_NOTHING,
                         {'returnType': expectedReturnType});
     }
     return const StatementType();
   }
 
   DartType visitThrow(Throw node) {
     // TODO(johnniwinther): Handle reachability.
     analyze(node.expression);
     return const DynamicType();
   }
 
-  /// Flatten [type] by recursively removing enclosing `Future` annotations.
-  ///
-  /// For instance:
-  ///     flatten(T) = T
-  ///     flatten(Future<T>) = T
-  ///     flatten(Future<Future<T>>) = T
-  ///
-  /// This method is used in the static typing of await and type checking of
-  /// return.
-  DartType flatten(DartType type) {
-    if (type is InterfaceType) {
-      InterfaceType futureType = type.asInstanceOf(compiler.futureClass);
-      if (futureType != null) {
-        return flatten(futureType.typeArguments.first);
-      }
-    }
-    return type;
-  }
-
   DartType visitAwait(Await node) {
     DartType expressionType = analyze(node.expression);
-    return flatten(expressionType);
+    return types.flatten(expressionType);
   }
 
   DartType visitYield(Yield node) {
     DartType resultType = analyze(node.expression);
     if (!node.hasStar) {
       if (currentAsyncMarker.isAsync) {
         resultType = coreTypes.streamType(resultType);
       } else {
         resultType = coreTypes.iterableType(resultType);
       }
@@ skipping 207 matching lines @@
 
   visitTypedef(Typedef node) {
     // Do not typecheck [Typedef] nodes.
   }
 
   visitNode(Node node) {
     compiler.internalError(node,
         'Unexpected node ${node.getObjectDescription()} in the type checker.');
   }
 }