GN: Don't allow nested things inside template invocations.

tools/gn/template.cc

 // Copyright 2014 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/template.h"
 
 #include "tools/gn/err.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
@@ skipping 23 matching lines @@
   if (!EnsureNotProcessingImport(invocation, scope, err))
     return Value();
 
   // First run the invocation's block. Need to allocate the scope on the heap
   // so we can pass ownership to the template.
   scoped_ptr<Scope> invocation_scope(new Scope(scope));
   if (!FillTargetBlockScope(scope, invocation,
                             invocation->function().value().as_string(),
                             block, args, invocation_scope.get(), err))
     return Value();
-  block->Execute(invocation_scope.get(), err);
-  if (err->has_error())
-    return Value();
+
+  {
+    // Don't allow the block of the template invocation to include other
+    // targets configs, or template invocations. This must only be applied
+    // to the invoker's block rather than the whole function because the
+    // template execution itself must be able to define targets, etc.
+    NonNestableBlock non_nestable(scope, invocation, "template invocation");
+    if (!non_nestable.Enter(err))
+      return Value();
+
+    block->Execute(invocation_scope.get(), err);
+    if (err->has_error())
+      return Value();
+  }
 
   // Set up the scope to run the template and set the current directory for the
   // template (which ScopePerFileProvider uses to base the target-related
   // variables target_gen_dir and target_out_dir on) to be that of the invoker.
   // This way, files don't have to be rebased and target_*_dir works the way
   // people expect (otherwise its to easy to be putting generated files in the
   // gen dir corresponding to an imported file).
   Scope template_scope(closure_.get());
   template_scope.set_source_dir(scope->GetSourceDir());
 
@@ skipping 48 matching lines @@
   // Check for unused variables in the template itself.
   if (!template_scope.CheckForUnusedVars(err))
     return Value();
 
   return result;
 }
 
 LocationRange Template::GetDefinitionRange() const {
   return definition_->GetRange();
 }