Re-land 125247: Better error messages when using unsupported manifest features.

chrome/common/extensions/feature.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_COMMON_EXTENSIONS_FEATURE_H_
 #define CHROME_COMMON_EXTENSIONS_FEATURE_H_
 #pragma once
 
 #include <set>
 #include <string>
@@ skipping 23 matching lines @@
     UNSPECIFIED_LOCATION,
     COMPONENT_LOCATION
   };
 
   // The platforms the feature is supported in.
   enum Platform {
     UNSPECIFIED_PLATFORM,
     CHROMEOS_PLATFORM
   };
 
+  // Whether a feature is available in a given situation or not, and if not,
+  // why not.
+  enum Availability {
+    IS_AVAILABLE,
+    NOT_FOUND_IN_WHITELIST,
+    INVALID_TYPE,
+    INVALID_CONTEXT,
+    INVALID_LOCATION,
+    INVALID_PLATFORM,
+    INVALID_MIN_MANIFEST_VERSION,
+    INVALID_MAX_MANIFEST_VERSION
+  };
+
   Feature();
   ~Feature();
 
   // Parses a feature from its JSON representation.
   static scoped_ptr<Feature> Parse(const DictionaryValue* value);
 
   // Gets the platform the code is currently running on.
   static Platform GetCurrentPlatform();
 
   // Gets the Feature::Location value for the specified Extension::Location.
@@ skipping 14 matching lines @@
     min_manifest_version_ = min_manifest_version;
   }
 
   int max_manifest_version() const { return max_manifest_version_; }
   void set_max_manifest_version(int max_manifest_version) {
     max_manifest_version_ = max_manifest_version;
   }
 
   // Returns true if the feature is available to the specified extension. Use
   // this overload for features that are not associated with a specific context.
-  bool IsAvailable(const Extension* extension) {
+  Availability IsAvailable(const Extension* extension) {
     return IsAvailable(extension, UNSPECIFIED_CONTEXT);
   }
 
   // Returns true if the feature is available to the specified extension, in the
   // specified context type.
-  bool IsAvailable(const Extension* extension, Context context) {
+  Availability IsAvailable(const Extension* extension, Context context) {
     return IsAvailable(extension->id(), extension->GetType(),
                        ConvertLocation(extension->location()), context,
                        GetCurrentPlatform(),
                        extension->manifest_version());
   }
 
   // Returns true if the feature is available to extensions with the specified
   // properties. Use this overload for features that are not associated with a
   // specific context, and when a full Extension object is not available.
-  bool IsAvailable(const std::string& extension_id, Extension::Type type,
-                   Location location, int manifest_version) {
+  Availability IsAvailable(const std::string& extension_id,
+                           Extension::Type type, Location location,
+                           int manifest_version) {
     return IsAvailable(extension_id, type, location, UNSPECIFIED_CONTEXT,
                        GetCurrentPlatform(), manifest_version);
   }
 
   // Returns true if the feature is available to extensions with the specified
   // properties, in the specified context type, and on the specified platform.
   // This overload is mainly used for testing.
-  bool IsAvailable(const std::string& extension_id, Extension::Type type,
-                   Location location, Context context,
-                   Platform platform, int manifest_version);
+  Availability IsAvailable(const std::string& extension_id,
+                           Extension::Type type, Location location,
+                           Context context, Platform platform,
+                           int manifest_version);
+
+  // Returns an error message for an Availability code.
+  std::string GetErrorMessage(Availability result);
 
  private:
   // For clarify and consistency, we handle the default value of each of these
   // members the same way: it matches everything. It is up to the higher level
   // code that reads Features out of static data to validate that data and set
   // sensible defaults.
   std::set<std::string> whitelist_;
   std::set<Extension::Type> extension_types_;
   std::set<Context> contexts_;
   Location location_;  // we only care about component/not-component now
   Platform platform_;  // we only care about chromeos/not-chromeos now
   int min_manifest_version_;
   int max_manifest_version_;
 
   DISALLOW_COPY_AND_ASSIGN(Feature);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_FEATURE_H_