Throw errors for nested targets in GN.

tools/gn/functions_target.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/functions.h"
 
 #include "tools/gn/config_values_generator.h"
 #include "tools/gn/err.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
@@ skipping 13 matching lines @@
 namespace functions {
 
 namespace {
 
 Value ExecuteGenericTarget(const char* target_type,
                            Scope* scope,
                            const FunctionCallNode* function,
                            const std::vector<Value>& args,
                            BlockNode* block,
                            Err* err) {
+  NonNestableBlock non_nestable(scope, function, "target");
+  if (!non_nestable.Enter(err))
+    return Value();
+
   if (!EnsureNotProcessingImport(function, scope, err) ||
       !EnsureNotProcessingBuildConfig(function, scope, err))
     return Value();
   Scope block_scope(scope);
   if (!FillTargetBlockScope(scope, function, target_type, block,
                             args, &block_scope, err))
     return Value();
 
   block->Execute(&block_scope, err);
   if (err->has_error())
@@ skipping 472 matching lines @@
   const Template* templ = scope->GetTemplate(target_type);
   if (templ)
     return templ->Invoke(scope, function, sub_args, block, err);
 
   // Otherwise, assume the target is a built-in target type.
   return ExecuteGenericTarget(target_type.c_str(), scope, function, sub_args,
                               block, err);
 }
 
 }  // namespace functions