Add initial prototype for the GN meta-buildsystem.

tools/gn/item_tree.h

Index: tools/gn/item_tree.h
diff --git a/tools/gn/item_tree.h b/tools/gn/item_tree.h
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+++ b/tools/gn/item_tree.h
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+// Copyright (c) 2013 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 TOOLS_GN_ITEM_TREE_H_
+#define TOOLS_GN_ITEM_TREE_H_
+
+#include "base/containers/hash_tables.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
+#include "tools/gn/label.h"
+
+class Err;
+class Item;
+class ItemNode;
+
+// Represents the full dependency tree if labeled items in the system.
+// Generally you will interact with this through the target manager, etc.
+class ItemTree {
+ public:
+  ItemTree();
+  ~ItemTree();
+
+  // This lock must be held when calling the "Locked" functions below.
+  base::Lock& lock() { return lock_; }
+
+  // Returns NULL if the item is not found.
+  //
+  // The lock must be held.
+  ItemNode* GetExistingNodeLocked(const Label& label);
+
+  // There must not be an item with this label in the tree already. Takes
+  // ownership of the pointer.
+  //
+  // The lock must be held.
+  void AddNodeLocked(ItemNode* node);
+
+  // Mark the given item as being generated. If it has no unresolved
+  // dependencies, it will be marked resolved, and the resolved state will be
+  // recursively pushed into the dependency tree. Returns an error if there was
+  // an error.
+  Err MarkItemGeneratedLocked(const Label& label);
+
+  // Fills the given vector with all known items.
+  void GetAllItemsLocked(std::vector<const Item*>* dest) const;
+
+  // Returns an error if there are unresolved dependencies, or no error if
+  // there aren't.
+  //
+  // The lock should not be held.
+  Err CheckForBadItems() const;
+
+ private:
+  Err MarkItemResolvedLocked(ItemNode* node);
+
+  // Given a set of unresolved nodes, looks for cycles and returns the error
+  // message describing any cycles it found.
+  std::string CheckForCircularDependenciesLocked(
+      const std::vector<const ItemNode*>& bad_nodes) const;
+
+  mutable base::Lock lock_;
+
+  typedef base::hash_map<Label, ItemNode*> StringToNodeHash;
+  StringToNodeHash items_;  // Owning pointer.
+
+  DISALLOW_COPY_AND_ASSIGN(ItemTree);
+};
+
+#endif  // TOOLS_GN_ITEM_TREE_H_