[Extension API Extern Generation] Fix a few bugs in extern generation

tools/json_schema_compiler/js_externs_generator.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 """
 Generator that produces an externs file for the Closure Compiler.
 Note: This is a work in progress, and generated externs may require tweaking.
 
 See https://developers.google.com/closure/compiler/docs/api-tutorial3#externs
 """
 
@@ skipping 16 matching lines @@
 class _Generator(object):
   def __init__(self, namespace):
     self._namespace = namespace
 
   def Generate(self):
     """Generates a Code object with the schema for the entire namespace.
     """
     c = Code()
     (c.Append(LICENSE)
         .Append()
         .Append('/** @fileoverview Externs generated from namespace: %s */' %

[Tyler Breisacher (Chromium), 2015/04/22 19:50:58]

Can we add some text here explaining HOW it was generated?

"Externs generated from tools/json_schema_compiler/js_externs_generator.py, from
namespace <namespace>"

or something. Bonus points if it tells you exactly how to run the thing to
regenerate it from the latest IDL.

                 self._namespace.name)
         .Append())
 
     c.Cblock(self._GenerateNamespaceObject())
 
     for js_type in self._namespace.types.values():
       c.Cblock(self._GenerateType(js_type))
 
     for function in self._namespace.functions.values():
       c.Cblock(self._GenerateFunction(function))
@@ skipping 71 matching lines @@
     c = Code()
     c.Append('@typedef {')
     c.Concat(self._GenerateObjectDefinition(properties), new_line=False)
     c.Append('}', new_line=False)
     return c
 
   def _GenerateObjectDefinition(self, properties):
     """Given an OrderedDict of properties, returns a Code containing the
        description of an object.
     """
-    if not properties: return ''
+    if not properties: return Code()
 
     c = Code()
     c.Sblock('{')
     first = True
     for field, prop in properties.items():
       # Avoid trailing comma.
       # TODO(devlin): This will be unneeded, if/when
       # https://github.com/google/closure-compiler/issues/796 is fixed.
       if not first:
         c.Append(',', new_line=False)
@@ skipping 65 matching lines @@
 
     if function.returns:
       c.Concat(self._TypeToJsType(function.returns), new_line=False)
     else:
       c.Append('void', new_line=False)
 
     return c
 
   def _TypeToJsType(self, js_type):
     """Converts a model.Type to a JS type (number, Array, etc.)"""
-    c = Code()
     if js_type.property_type in (PropertyType.INTEGER, PropertyType.DOUBLE):
-      c.Append('number')
-    elif js_type.property_type is PropertyType.OBJECT:
-      c = self._GenerateObjectDefinition(js_type.properties)
-    elif js_type.property_type is PropertyType.ARRAY:
-      (c.Append('!Array<').
+      return Code().Append('number')
+    if js_type.property_type is PropertyType.OBJECT:
+      if js_type.properties:
+        return self._GenerateObjectDefinition(js_type.properties)
+      return Code().Append('Object')
+    if js_type.property_type is PropertyType.ARRAY:
+      return (Code().Append('!Array<').
            Concat(self._TypeToJsType(js_type.item_type), new_line=False).
            Append('>', new_line=False))
-    elif js_type.property_type is PropertyType.REF:
+    if js_type.property_type is PropertyType.REF:
       ref_type = js_type.ref_type
       # Enums are defined as chrome.fooAPI.MyEnum, but types are defined simply
       # as MyType.
       if self._namespace.types[ref_type].property_type is PropertyType.ENUM:
         ref_type = '!chrome.%s.%s' % (self._namespace.name, ref_type)
-      c.Append(ref_type)
-    elif js_type.property_type is PropertyType.CHOICES:
+      return Code().Append(ref_type)
+    if js_type.property_type is PropertyType.CHOICES:
+      c = Code()
       c.Append('(')
       for i, choice in enumerate(js_type.choices):
         c.Concat(self._TypeToJsType(choice), new_line=False)
         if i is not len(js_type.choices) - 1:
           c.Append('|', new_line=False)
       c.Append(')', new_line=False)
-    elif js_type.property_type is PropertyType.FUNCTION:
-      c = self._FunctionToJsFunction(js_type.function)
-    elif js_type.property_type is PropertyType.ANY:
-      c.Append('*')
-    elif js_type.property_type.is_fundamental:
-      c.Append(js_type.property_type.name)
-    else:
-      c.Append('?') # TODO(tbreisacher): Make this more specific.
-    return c
+      return c
+    if js_type.property_type is PropertyType.FUNCTION:
+      return self._FunctionToJsFunction(js_type.function)
+    if js_type.property_type is PropertyType.ANY:
+      return Code().Append('*')
+    if js_type.property_type.is_fundamental:
+      return Code().Append(js_type.property_type.name)
+    return Code().Append('?') # TODO(tbreisacher): Make this more specific.
 
   def _GenerateFunction(self, function):
     """Generates the code representing a function, including its documentation.
        For example:
 
        /**
         * @param {string} title The new title.
         */
        chrome.window.setTitle = function(title) {};
     """
@@ skipping 49 matching lines @@
     """Generates a @see link for a given API 'object' (type, method, or event).
     """
 
     # NOTE(devlin): This is kind of a hack. Some APIs will be hosted on
     # developer.chrome.com/apps/ instead of /extensions/, and some APIs have
     # '.'s in them (like app.window), which should resolve to 'app_window'.
     # Luckily, the doc server has excellent url resolution, and knows exactly
     # what we mean. This saves us from needing any complicated logic here.
     return ('@see https://developer.chrome.com/extensions/%s#%s-%s' %
                 (self._namespace.name, object_type, object_name))