Support more configurability in GN toolchains

tools/gn/builder.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/builder.h"
 
 #include "tools/gn/config.h"
 #include "tools/gn/err.h"
 #include "tools/gn/loader.h"
 #include "tools/gn/scheduler.h"
@@ skipping 390 matching lines @@
 bool Builder::ResolveItem(BuilderRecord* record, Err* err) {
   DCHECK(record->can_resolve() && !record->resolved());
 
   if (record->type() == BuilderRecord::ITEM_TARGET) {
     Target* target = record->item()->AsTarget();
     if (!ResolveDeps(&target->deps(), err) ||
         !ResolveDeps(&target->datadeps(), err) ||
         !ResolveConfigs(&target->configs(), err) ||
         !ResolveConfigs(&target->all_dependent_configs(), err) ||
         !ResolveConfigs(&target->direct_dependent_configs(), err) ||
-        !ResolveForwardDependentConfigs(target, err))
+        !ResolveForwardDependentConfigs(target, err) ||
+        !ResolveToolchain(target, err))
       return false;
   } else if (record->type() == BuilderRecord::ITEM_TOOLCHAIN) {
     Toolchain* toolchain = record->item()->AsToolchain();
     if (!ResolveDeps(&toolchain->deps(), err))
       return false;
   }
 
   record->set_resolved(true);
   record->item()->OnResolved();
   if (!resolved_callback_.is_null())
@@ skipping 70 matching lines @@
           "This target has a forward_dependent_configs_from entry that was "
           "not present in\nthe deps. A target can only forward things it "
           "depends on. It was forwarding:\n  " +
           configs[config_i].label.GetUserVisibleName(false));
       return false;
     }
   }
   return true;
 }
 
+bool Builder::ResolveToolchain(Target* target, Err* err) {
+  BuilderRecord* record = GetResolvedRecordOfType(
+      target->settings()->toolchain_label(), target->defined_from(),
+      BuilderRecord::ITEM_TOOLCHAIN, err);
+  if (!record) {
+    *err = Err(target->defined_from(),
+        "Toolchain for target not defined.",
+        "I was hoping to find a toolchain " +
+        target->settings()->toolchain_label().GetUserVisibleName(false));
+    return false;
+  }
+
+  if (!target->SetToolchain(record->item()->AsToolchain(), err))
+    return false;
+
+  return true;
+}
+
 std::string Builder::CheckForCircularDependencies(
     const std::vector<const BuilderRecord*>& bad_records) const {
   std::vector<const BuilderRecord*> cycle;
   if (!RecursiveFindCycle(bad_records[0], &cycle))
     return std::string();  // Didn't find a cycle, something else is wrong.
 
   // Walk backwards since the dependency arrows point in the reverse direction.
   std::string ret;
   for (int i = static_cast<int>(cycle.size()) - 1; i >= 0; i--) {
     ret += "  " + cycle[i]->label().GetUserVisibleName(false);
     if (i != 0)
       ret += " ->\n";
   }
 
   return ret;
 }