[WIP] Disable and Restore the Preprocessor's macro expansion in

FrontendAction's BeginSourceFileAction and EndSourceFileAction

Author: jmmartinez

clang/include/clang/Frontend/FrontendAction.h

@@ -85,7 +85,7 @@ class FrontendAction {
   /// EndSourceFileAction() will not be called.
   virtual bool BeginSourceFileAction(CompilerInstance &CI) {
     if (CurrentInput.isPreprocessed())
-      CI.getPreprocessor().SetDisableMacroExpansion();
+      CI.getPreprocessor().SetEnableMacroExpansion(false);
     return true;
   }
 
@@ -100,7 +100,11 @@ class FrontendAction {
   ///
   /// This is guaranteed to only be called following a successful call to
   /// BeginSourceFileAction (and BeginSourceFile).
-  virtual void EndSourceFileAction() {}
+  virtual void EndSourceFileAction() {
+    if (CurrentInput.isPreprocessed())
+      // reset the preprocessor macro expansion to the default
+      getCompilerInstance().getPreprocessor().SetEnableMacroExpansion(true);
+  }
 
   /// Callback at the end of processing a single input, to determine
   /// if the output files should be erased or not.

clang/include/clang/Lex/Preprocessor.h

@@ -1831,10 +1831,7 @@ class Preprocessor {
     MacroExpansionInDirectivesOverride = true;
   }
 
-  void SetDisableMacroExpansion() {
-    DisableMacroExpansion = true;
-    MacroExpansionInDirectivesOverride = false;
-  }
+  void SetEnableMacroExpansion(bool Enable) { DisableMacroExpansion = !Enable; }
 
   /// Peeks ahead N tokens and returns that token without consuming any
   /// tokens.