[Review] Disable macro expansion in BeginSourceFileAction

Author: jmmartinez

clang/include/clang/Frontend/FrontendAction.h

@@ -84,6 +84,8 @@ class FrontendAction {
   /// \return True on success; on failure ExecutionAction() and
   /// EndSourceFileAction() will not be called.
   virtual bool BeginSourceFileAction(CompilerInstance &CI) {
+    if (CurrentInput.isPreprocessed())
+      CI.getPreprocessor().SetDisableMacroExpansion();
     return true;
   }
 

clang/lib/Frontend/InitPreprocessor.cpp

@@ -1559,12 +1559,6 @@ void clang::InitializePreprocessor(Preprocessor &PP,
                                    const FrontendOptions &FEOpts,
                                    const CodeGenOptions &CodeGenOpts) {
 
-  if (all_of(FEOpts.Inputs,
-             [](const FrontendInputFile &FI) { return FI.isPreprocessed(); })) {
-    PP.SetDisableMacroExpansion();
-    return;
-  }
-
   const LangOptions &LangOpts = PP.getLangOpts();
   std::string PredefineBuffer;
   PredefineBuffer.reserve(4080);