[clang][DependencyScanning] Add API to expose module CompilerInvocation

Add a new API that returns underlying CompilerInvocation from ModuleDep.
This allows clients to inspect and modify the state inside
CompilerInvocation before turning that into build arguments.

Author: cachemeifyoucan

clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h

@@ -183,6 +183,11 @@ struct ModuleDeps {
   /// module. Does not include argv[0].
   const std::vector<std::string> &getBuildArguments() const;
 
+  /// Experimental: get the underlying CompilerInvocation before calling
+  /// `getBuildArguments`. This provides a short cut to inspect/modify the
+  /// compiler invocation state before turning into build command.
+  CowCompilerInvocation &getUnderlyingCompilerInvocation() const;
+
 private:
   friend class ModuleDepCollector;
   friend class ModuleDepCollectorPP;

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

@@ -46,6 +46,12 @@ const std::vector<std::string> &ModuleDeps::getBuildArguments() const {
   return std::get<std::vector<std::string>>(BuildInfo);
 }
 
+CowCompilerInvocation &ModuleDeps::getUnderlyingCompilerInvocation() const {
+  assert(std::holds_alternative<CowCompilerInvocation>(BuildInfo) &&
+         "ModuleDeps doesn't hold compiler invocation");
+  return *std::get_if<CowCompilerInvocation>(&BuildInfo);
+}
+
 static void
 optimizeHeaderSearchOpts(HeaderSearchOptions &Opts, ASTReader &Reader,
                          const serialization::ModuleFile &MF,