Allow manifest handlers to declare keys they depend on that must be parsed before them.

chrome/common/extensions/manifest_handler.cc

Index: chrome/common/extensions/manifest_handler.cc
diff --git a/chrome/common/extensions/manifest_handler.cc b/chrome/common/extensions/manifest_handler.cc
index c1c76131850c12c038ddacfe4f5c84fb759b191b..bbf17be40d75ba4ef8b964bddfe4679e6d448114 100644
--- a/chrome/common/extensions/manifest_handler.cc
+++ b/chrome/common/extensions/manifest_handler.cc
@@ -7,7 +7,7 @@
 #include <map>
 
 #include "base/lazy_instance.h"
-#include "base/memory/linked_ptr.h"
+#include "base/stl_util.h"
 #include "chrome/common/extensions/manifest.h"
 
 namespace extensions {
@@ -16,48 +16,139 @@ namespace {
 
 class ManifestHandlerRegistry {
  public:
+  ManifestHandlerRegistry() : is_sorted_(false) {
+  }
+
   void RegisterManifestHandler(const std::string& key,
-                               ManifestHandler* handler);
+                               linked_ptr<ManifestHandler> handler);
   bool ParseExtension(Extension* extension, string16* error);
+  void ClearForTesting();
 
  private:
   friend struct base::DefaultLazyInstanceTraits<ManifestHandlerRegistry>;
   typedef std::map<std::string, linked_ptr<ManifestHandler> >
       ManifestHandlerMap;
+  typedef std::map<ManifestHandler*, int> ManifestHandlerPriorityMap;
+
+  // Puts the manifest handlers in order such that each handler comes after
+  // any handlers for their PrerequisiteKeys. If there is no handler for
+  // a prerequisite key, that dependency is simply ignored.
+  // Manifest handlers with circular dependencies are unregistered.
+  void SortManifestHandlers();
 
+  // All registered manifest handlers.
   ManifestHandlerMap handlers_;
+
+  // The priority for each manifest handler. Handlers with lower priority
+  // values are evaluated first.
+  ManifestHandlerPriorityMap priority_map_;
+  bool is_sorted_;
 };
 
 void ManifestHandlerRegistry::RegisterManifestHandler(
-    const std::string& key, ManifestHandler* handler) {
-  handlers_[key] = make_linked_ptr(handler);
+    const std::string& key, linked_ptr<ManifestHandler> handler) {
+  handlers_[key] = handler;
+  is_sorted_ = false;
 }
 
 bool ManifestHandlerRegistry::ParseExtension(Extension* extension,
                                              string16* error) {
-  std::set<ManifestHandler*> handler_set;
+  SortManifestHandlers();
+  std::map<int, ManifestHandler*> handlers_by_priority;
   for (ManifestHandlerMap::iterator iter = handlers_.begin();
        iter != handlers_.end(); ++iter) {
     ManifestHandler* handler = iter->second.get();
     if (extension->manifest()->HasPath(iter->first) ||
-        handler->AlwaysParseForType(extension->GetType()))
-      handler_set.insert(handler);
+        handler->AlwaysParseForType(extension->GetType())) {
+      handlers_by_priority[priority_map_[handler]] = handler;
+    }
   }
-
-  // TODO(yoz): Some handlers may depend on other handlers having already
-  // parsed their keys. Reorder the handlers so that handlers needed earlier
-  // come first in the returned container.
-  for (std::set<ManifestHandler*>::iterator iter = handler_set.begin();
-       iter != handler_set.end(); ++iter) {
-    if (!(*iter)->Parse(extension, error))
+  for (std::map<int, ManifestHandler*>::iterator iter =
+           handlers_by_priority.begin();
+       iter != handlers_by_priority.end(); ++iter) {
+    if (!(iter->second)->Parse(extension, error))
       return false;
   }
   return true;
 }
 
+void ManifestHandlerRegistry::ClearForTesting() {
+  priority_map_.clear();
+  handlers_.clear();
+  is_sorted_ = false;
+}
+
+void ManifestHandlerRegistry::SortManifestHandlers() {
+  if (is_sorted_)
+    return;
+
+  // Forget our existing sort order.
+  priority_map_.clear();
+  std::set<ManifestHandler*> unsorted_handlers;
+  for (ManifestHandlerMap::const_iterator iter = handlers_.begin();
+       iter != handlers_.end(); ++iter) {
+    unsorted_handlers.insert(iter->second.get());
+  }
+
+  int priority = 0;
+  while (true) {
+    std::set<ManifestHandler*> next_unsorted_handlers;
+    for (std::set<ManifestHandler*>::const_iterator iter =
+             unsorted_handlers.begin();
+         iter != unsorted_handlers.end(); ++iter) {
+      ManifestHandler* handler = *iter;
+      const std::vector<std::string>& prerequisites =
+          handler->PrerequisiteKeys();
+      int unsatisfied = prerequisites.size();
+      for (size_t i = 0; i < prerequisites.size(); ++i) {
+        ManifestHandlerMap::const_iterator prereq_iter =
+            handlers_.find(prerequisites[i]);
+        if (prereq_iter == handlers_.end()) {
+          // Nonexistent prerequisite; ignore it.
+          unsatisfied--;
+        } else if (ContainsKey(priority_map_,
+                               prereq_iter->second.get())) {
+          // Prerequisite is in our map.
+          unsatisfied--;
+        }
+      }
+      if (unsatisfied == 0) {
+        priority_map_[handler] = priority;
+        priority++;
+      } else {
+        // Put in the list for next time.
+        next_unsorted_handlers.insert(handler);
+      }
+    }
+    if (next_unsorted_handlers.size() == unsorted_handlers.size())
+      break;
+    unsorted_handlers.swap(next_unsorted_handlers);
+  }
+
+  // If there are any leftover unsorted handlers, they must have had
+  // circular dependencies. Drop them, and log a warning.

[Yoyo Zhou, 2013/02/01 22:16:42]

I'm not sure this is the best way to deal with this. Here are some possible
alternatives:

(0) Log the error message in some less ugly way.
(1) NOTREACHED. Not sure this is worth crashing the browser over, but
profile_dependency_manager does take this approach. Hard to unit test.
(2) Reject a manifest handler when it Registers if it tries to create a circular
dependency. This forces us to SortManifestHandlers at every registration (though
some heuristics could reduce this).

+  if (unsorted_handlers.size() > 0) {
+    LOG(WARNING) << "Ignoring extension manifest handlers with "
+                 << "circular dependencies:";
+    for (ManifestHandlerMap::iterator iter = handlers_.begin();
+         iter != handlers_.end();) {
+      ManifestHandlerMap::iterator current = iter++;
+      if (ContainsKey(unsorted_handlers, current->second.get())) {
+        LOG(WARNING) << "key: " << current->first;
+        handlers_.erase(current);
+      }
+    }
+  }
+
+  is_sorted_ = true;
+}
+
 static base::LazyInstance<ManifestHandlerRegistry> g_registry =
     LAZY_INSTANCE_INITIALIZER;
 
+static base::LazyInstance<std::vector<std::string> > g_empty_string_vector =
+    LAZY_INSTANCE_INITIALIZER;
+
 }  // namespace
 
 ManifestHandler::ManifestHandler() {
@@ -70,9 +161,13 @@ bool ManifestHandler::AlwaysParseForType(Manifest::Type type) {
   return false;
 }
 
+const std::vector<std::string>& ManifestHandler::PrerequisiteKeys() {
+  return g_empty_string_vector.Get();
+}
+
 // static
 void ManifestHandler::Register(const std::string& key,
-                               ManifestHandler* handler) {
+                               linked_ptr<ManifestHandler> handler) {
   g_registry.Get().RegisterManifestHandler(key, handler);
 }
 
@@ -81,4 +176,9 @@ bool ManifestHandler::ParseExtension(Extension* extension, string16* error) {
   return g_registry.Get().ParseExtension(extension, error);
 }
 
+// static
+void ManifestHandler::ClearRegistryForTesting() {
+  g_registry.Get().ClearForTesting();
+}
+
 }  // namespace extensions