dart2js: Make .runtimeType work for tear-off closures

sdk/lib/_internal/js_runtime/lib/js_rti.dart

Index: sdk/lib/_internal/js_runtime/lib/js_rti.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_rti.dart b/sdk/lib/_internal/js_runtime/lib/js_rti.dart
index f9cd6985f06bedc837c40f3ac4961bf4b436992b..2ba517c334044a9ad4cbd6254e05a4821e0ebcf8 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_rti.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_rti.dart
@@ -159,22 +159,95 @@ String getRuntimeTypeAsString(var rti, {String onTypeVariable(int i)}) {
 String runtimeTypeToString(var rti, {String onTypeVariable(int i)}) {
   if (rti == null) {
     return 'dynamic';
-  } else if (isJsArray(rti)) {
+  }
+  if (isJsArray(rti)) {
     // A list representing a type with arguments.
     return getRuntimeTypeAsString(rti, onTypeVariable: onTypeVariable);
-  } else if (isJsFunction(rti)) {
+  }
+  if (isJsFunction(rti)) {
     // A reference to the constructor.
     return rawRtiToJsConstructorName(rti);
-  } else if (rti is int) {
+  }
+  if (rti is int) {
     if (onTypeVariable == null) {
       return rti.toString();
     } else {
       return onTypeVariable(rti);
     }
+  }
+  if (JS('bool', 'typeof #.func != "undefined"', rti)) {
+    // If the RTI has typedef equivalence info (via mirrors), use that since the
+    // mirrors helpers will re-parse the generated string.
+
+    String typedefPropertyName = JS_GET_NAME(JsGetName.TYPEDEF_TAG);
+    var typedefInfo = JS('', '#[#]', rti, typedefPropertyName);
+    if (typedefInfo != null) {
+      return runtimeTypeToString(typedefInfo, onTypeVariable: onTypeVariable);
+    }
+    return _functionRtiToString(rti, onTypeVariable);
+  }
+  // We should not get here.
+  return 'unknown-reified-type';
+}
+
+String _functionRtiToString(var rti, String onTypeVariable(int i)) {
+  String returnTypeText;
+  if (JS('bool', '!!#.v', rti)) {
+    returnTypeText = 'void';
   } else {
-    // TODO(ahe): Handle function types, and be sure to always return a string.
-    return null;
+    var returnRti = JS('', '#.ret', rti);
+    returnTypeText =
+        runtimeTypeToString(returnRti, onTypeVariable: onTypeVariable);
+  }
+
+  String argumentsText = '';
+  String sep = '';
+
+  bool hasArguments = JS('bool', '"args" in #', rti);
+  if (hasArguments) {
+    List arguments = JS('JSFixedArray', '#.args', rti);
+    for (var argument in arguments) {
+      argumentsText += sep;
+      argumentsText +=
+          runtimeTypeToString(argument, onTypeVariable: onTypeVariable);
+      sep = ', ';
+    }
+  }
+
+  bool hasOptionalArguments = JS('bool', '"opt" in #', rti);
+  if (hasOptionalArguments) {
+    List optionalArguments = JS('JSFixedArray', '#.opt', rti);
+    argumentsText += '$sep[';
+    sep = '';
+    for (var argument in optionalArguments) {
+      argumentsText += sep;
+      argumentsText +=
+          runtimeTypeToString(argument, onTypeVariable: onTypeVariable);
+      sep = ', ';
+    }
+    argumentsText += ']';
   }
+
+  bool hasNamedArguments = JS('bool', '"named" in #', rti);
+  if (hasNamedArguments) {
+    var namedArguments = JS('', '#.named', rti);
+    argumentsText += '$sep{';
+    sep = '';
+    for (String name in extractKeys(namedArguments)) {
+      argumentsText += sep;
+      argumentsText += runtimeTypeToString(JS('', '#[#]', namedArguments, name),
+                                           onTypeVariable: onTypeVariable);
+      argumentsText += ' $name';
+      sep = ', ';
+    }
+    argumentsText += '}';
+  }
+
+  // TODO(sra): Below is the same format as the VM. Change to:
+  //
+  //     '${returnTypeText} Function(${argumentsText})';
+  //
+  return '(${argumentsText}) => ${returnTypeText}';
 }
 
 /**
@@ -210,6 +283,10 @@ String joinArguments(var types, int startIndex,
  * In minified mode does *not* use unminified identifiers (even when present).
  */
 String getRuntimeTypeString(var object) {
+  // Check for function type first, since non-tearoff closures look like classes
+  // due to closure conversion.
+  var functionRti = extractFunctionTypeObjectFrom(object);
+  if (functionRti != null) return runtimeTypeToString(functionRti);
   String className = getClassName(object);
   if (object == null) return className;
   var rti = JS('var', r'#.$ti', object);