Implement tracking of BUILD.gn files used to define target, toolchain or

tools/gn/import_manager.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/import_manager.h"
 
 #include "tools/gn/err.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scheduler.h"
 #include "tools/gn/scope_per_file_provider.h"
 #include "tools/gn/trace.h"
 
 namespace {
 
 // Returns a newly-allocated scope on success, null on failure.
 std::unique_ptr<Scope> UncachedImport(const Settings* settings,
                                       const SourceFile& file,
                                       const ParseNode* node_for_err,
                                       Err* err) {
   ScopedTrace load_trace(TraceItem::TRACE_IMPORT_LOAD, file.value());
 
   const ParseNode* node = g_scheduler->input_file_manager()->SyncLoadFile(
       node_for_err->GetRange(), settings->build_settings(), file, err);
   if (!node)
     return nullptr;
 
   std::unique_ptr<Scope> scope(new Scope(settings->base_config()));
   scope->set_source_dir(file.GetDir());
 
+  const Location& location = node->GetRange().begin();
+  if (!location.is_null())
+    scope->AddInputFile(location.file());
+
   // Don't allow ScopePerFileProvider to provide target-related variables.
   // These will be relative to the imported file, which is probably not what
   // people mean when they use these.
   ScopePerFileProvider per_file_provider(scope.get(), false);
 
   scope->SetProcessingImport();
   node->Execute(scope.get(), err);
   if (err->has_error()) {
     // If there was an error, append the caller location so the error message
     // displays a why the file was imported (esp. useful for failed asserts).
@@ skipping 91 matching lines @@
                                            "import", err);
 }
 
 std::vector<SourceFile> ImportManager::GetImportedFiles() const {
   std::vector<SourceFile> imported_files;
   imported_files.resize(imports_.size());
   std::transform(imports_.begin(), imports_.end(), imported_files.begin(),
                  [](const ImportMap::value_type& val) { return val.first; });
   return imported_files;
 }