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

tools/gn/analyzer.cc

Index: tools/gn/analyzer.cc
diff --git a/tools/gn/analyzer.cc b/tools/gn/analyzer.cc
index aa0eca4d1c1c882fe8ede2bb00b81ef7cf8ebce9..7ed6871a2b6e3926156c458a89ae7d6063285dc7 100644
--- a/tools/gn/analyzer.cc
+++ b/tools/gn/analyzer.cc
@@ -56,12 +56,9 @@ LabelSet LabelsFor(const TargetSet& targets) {
   return labels;
 }
 
-bool AnyBuildFilesWereModified(const SourceFileSet& source_files) {
+bool DotGNFileWasModified(const SourceFileSet& source_files) {
   for (auto* file : source_files) {
-    if (base::EndsWith(file->value(), ".gn", base::CompareCase::SENSITIVE) ||
-        base::EndsWith(file->value(), ".gni", base::CompareCase::SENSITIVE) ||
-        base::EndsWith(file->value(), "build/vs_toolchain.py",
-                       base::CompareCase::SENSITIVE))
+    if (file->value() == "//.gn")
       return true;
   }
   return false;
@@ -262,12 +259,7 @@ std::string Analyzer::Analyze(const std::string& input, Err* err) const {
     return OutputsToJSON(outputs, default_toolchain_, err);
   }
 
-  // TODO(crbug.com/555273): We can do smarter things when we detect changes
-  // to build files. For example, if all of the ninja files are unchanged,
-  // we know that we can ignore changes to .gn* files. Also, for most .gn
-  // files, we can treat a change as simply affecting every target, config,
-  // or toolchain defined in that file.
-  if (AnyBuildFilesWereModified(inputs.source_files)) {
+  if (DotGNFileWasModified(inputs.source_files)) {
     outputs.status = "Found dependency (all)";
     if (inputs.compile_included_all) {
       outputs.compile_includes_all = true;
@@ -360,6 +352,10 @@ void Analyzer::FilterTarget(const Target* target,
 
 bool Analyzer::TargetRefersToFile(const Target* target,
                                   const SourceFile* file) const {
+  const auto& source_files_hashes = target->source_files_hashes();
+  if (source_files_hashes.find(base::Hash(file->value())) !=
+      source_files_hashes.end())
+    return true;
   for (const auto& cur_file : target->sources()) {
     if (cur_file == *file)
       return true;