Add initial prototype for the GN meta-buildsystem.

tools/gn/config.cc

Index: tools/gn/config.cc
diff --git a/tools/gn/config.cc b/tools/gn/config.cc
new file mode 100644
index 0000000000000000000000000000000000000000..1175d7f3c8bf66e528969893e45e9a07850b8a53
--- /dev/null
+++ b/tools/gn/config.cc
@@ -0,0 +1,78 @@
+// 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.
+
+#include "tools/gn/config.h"
+
+#include "tools/gn/err.h"
+#include "tools/gn/input_file_manager.h"
+#include "tools/gn/item_node.h"
+#include "tools/gn/item_tree.h"
+#include "tools/gn/scheduler.h"
+
+Config::Config(const Label& label) : Item(label) {
+}
+
+Config::~Config() {
+}
+
+Config* Config::AsConfig() {
+  return this;
+}
+
+const Config* Config::AsConfig() const {
+  return this;
+}
+
+// static
+Config* Config::GetConfig(const Settings* settings,
+                          const LocationRange& specified_from_here,
+                          const Label& label,
+                          Item* dep_from,
+                          Err* err) {
+  DCHECK(!label.is_null());
+
+  ItemTree* tree = &settings->build_settings()->item_tree();
+  base::AutoLock lock(tree->lock());
+
+  ItemNode* node = tree->GetExistingNodeLocked(label);
+  Config* config = NULL;
+  if (!node) {
+    config = new Config(label);
+    node = new ItemNode(config);
+    tree->AddNodeLocked(node);
+
+    // Only schedule loading the given target if somebody is depending on it
+    // (and we optimize by not re-asking it to run the current file).
+    // Otherwise, we're probably generating it right now.
+    if (dep_from && dep_from->label().dir() != label.dir()) {
+      settings->build_settings()->toolchain_manager().ScheduleInvocationLocked(
+          specified_from_here, label.GetToolchainLabel(), label.dir(),
+          err);
+    }
+  } else if ((config = node->item()->AsConfig())) {
+    // Previously saw this item as a config.
+
+    // If we have no dep_from, we're generating it. In this case, it had better
+    // not already be generated.
+    if (!dep_from && node->state() != ItemNode::REFERENCED) {
+      *err = Err(specified_from_here, "Duplicate config definition.",
+          "You already told me about a config with this name.");
+      return NULL;
+    }
+  } else {
+    // Previously saw this thing as a non-config.
+    *err = Err(specified_from_here,
+               "Config name already used.",
+               "Previously you specified a " +
+               node->item()->GetItemTypeName() + " with this name instead.");
+    return NULL;
+  }
+
+  // Keep a record of the guy asking us for this dependency. We know if
+  // somebody is adding a dependency, that guy it himself not resolved.
+  if (dep_from && node->state() != ItemNode::RESOLVED)
+    tree->GetExistingNodeLocked(dep_from->label())->AddDependency(node);
+
+  return config;
+}