Allow dependencies of toolchains in GN.

tools/gn/function_toolchain.cc

 // 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/err.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scheduler.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/settings.h"
 #include "tools/gn/toolchain.h"
+#include "tools/gn/value_extractors.h"
 #include "tools/gn/variables.h"
 
 namespace functions {
 
 namespace {
 
 // This is jsut a unique value to take the address of to use as the key for
 // the toolchain property on a scope.
 const int kToolchainPropertyKey = 0;
 
@@ skipping 22 matching lines @@
     "\n"
     "  A toolchain is a set of commands and build flags used to compile the\n"
     "  source code. You can have more than one toolchain in use at once in\n"
     "  a build.\n"
     "\n"
     "  A toolchain specifies the commands to run for various input file\n"
     "  types via the \"tool\" call (see \"gn help tool\") and specifies\n"
     "  arguments to be passed to the toolchain build via the\n"
     "  \"toolchain_args\" call (see \"gn help toolchain_args\").\n"
     "\n"
+    "  In addition, a toolchain can specify dependencies via the \"deps\"\n"
+    "  variable like a target. These dependencies will be resolved before any\n"
+    "  target in the toolchain is compiled. To avoid circular dependencies\n"
+    "  these must be targets defined in another toolchain.\n"
+    "\n"
     "Invoking targets in toolchains:\n"
     "\n"
     "  By default, when a target depends on another, there is an implicit\n"
     "  toolchain label that is inherited, so the dependee has the same one\n"
     "  as the dependent.\n"
     "\n"
     "  You can override this and refer to any other toolchain by explicitly\n"
     "  labeling the toolchain to use. For example:\n"
     "    datadeps = [ \"//plugins:mine(//toolchains:plugin_toolchain)\" ]\n"
     "  The string \"//build/toolchains:plugin_toolchain\" is a label that\n"
@@ skipping 45 matching lines @@
   toolchain->set_defined_from(function);
   toolchain->visibility().SetPublic();
 
   Scope block_scope(scope);
   block_scope.SetProperty(&kToolchainPropertyKey, toolchain.get());
   block->ExecuteBlockInScope(&block_scope, err);
   block_scope.SetProperty(&kToolchainPropertyKey, NULL);
   if (err->has_error())
     return Value();
 
+  // Read deps (if any).
+  const Value* deps_value = block_scope.GetValue(variables::kDeps, true);
+  if (deps_value) {
+    ExtractListOfLabels(
+        *deps_value, block_scope.GetSourceDir(),
+        ToolchainLabelForScope(&block_scope), &toolchain->deps(), err);
+    if (err->has_error())
+      return Value();
+  }
+
+
   if (!block_scope.CheckForUnusedVars(err))
     return Value();
 
-  // Save this target for the file.
+  // Save this toolchain.
   Scope::ItemVector* collector = scope->GetItemCollector();
   if (!collector) {
     *err = Err(function, "Can't define a toolchain in this context.");
     return Value();
   }
   collector->push_back(new scoped_ptr<Item>(toolchain.PassAs<Item>()));
   return Value();
 }
 
 // tool ------------------------------------------------------------------------
@@ skipping 174 matching lines @@
     return Value();
 
   Scope::KeyValueMap values;
   block_scope.GetCurrentScopeValues(&values);
   toolchain->args() = values;
 
   return Value();
 }
 
 }  // namespace functions