support the JS builtin

lib/src/checker/resolver.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.
 
 /// Encapsulates how to invoke the analyzer resolver and overrides how it
 /// computes types on expressions to use our restricted set of types.
 library ddc.src.checker.resolver;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 345 matching lines @@
     // otherLib.visibleLibraries.contains(thisLib), however because we are not
     // inferring type on any library that belongs to a cycle or that contains
     // parts, we know that this cannot be true.
     return thisLib == otherLib;
   }
 
   @override // to propagate types to identifiers
   visitMethodInvocation(MethodInvocation node) {
     // TODO(sigmund): follow up with analyzer team - why is this needed?
     visitSimpleIdentifier(node.methodName);
-    return super.visitMethodInvocation(node);
+    super.visitMethodInvocation(node);
+
+    var e = node.methodName.staticElement;
+    if (e is FunctionElement &&
+        e.library.name == '_foreign_helper' &&
+        e.name == 'JS') {
+      // Fix types for JS builtin calls.
+      //
+      // This code was taken from analyzer. It's not super sophisticated:
+      // only looks for the type name in dart:core, so we just copy it here.
+      //
+      // TODO(jmesserly): we'll likely need something that can handle a wider
+      // variety of types, especially when we get to JS interop.
+      var args = node.argumentList.arguments;
+      if (args.isNotEmpty && args.first is SimpleStringLiteral) {
+        var coreLib = _typeProvider.objectType.element.library;
+        var classElem = coreLib.getType(args.first.stringValue);
+        if (classElem != null) node.staticType = classElem.type;
+      }
+    }
   }
 
   // Review note: no longer need to override visitFunctionExpression, this is
   // handled by the analyzer internally.
   // TODO(vsm): in visitbinaryExpression: check computeStaticReturnType result?
   // TODO(vsm): in visitConditionalExpression: check... LUB in rules?
   // TODO(vsm): in visitFunctionDeclaration: Should we ever use the expression
   // type in a (...) => expr or just the written type?
 
 }
@@ skipping 42 matching lines @@
         element.returnType.isDynamic &&
         node.returnType == null) {
       var type = searchTypeFor(element.enclosingElement.type, element);
       if (type != null && !type.returnType.isDynamic) {
         element.returnType = type.returnType;
       }
     }
     return res;
   }
 }