[Lex] Allow to consume tokens while preprocessing

Summary:
By adding a hook to consume all tokens produced by the preprocessor.
The intention of this change is to make it possible to consume the
expanded tokens without re-runnig the preprocessor with minimal changes
to the preprocessor and minimal performance penalty when preprocessing
without recording the tokens.

The added hook is very low-level and reconstructing the expanded token
stream requires more work in the client code, the actual algorithm to
collect the tokens using this hook can be found in the follow-up change.

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: eraman, nemanjai, kbarton, jsji, riccibruno, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D59885

llvm-svn: 361007

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Frontend/PrintPreprocessedOutput.cpp b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
index 584f94db133..720ed51c5f6 100644
--- a/clang/lib/Frontend/PrintPreprocessedOutput.cpp
+++ b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
@@ -678,7 +678,8 @@ struct UnknownPragmaHandler : public PragmaHandler {
       auto Toks = llvm::make_unique<Token[]>(1);
       Toks[0] = PragmaTok;
       PP.EnterTokenStream(std::move(Toks), /*NumToks=*/1,
-                          /*DisableMacroExpansion=*/false);
+                          /*DisableMacroExpansion=*/false,
+                          /*IsReinject=*/false);
       PP.Lex(PragmaTok);
     }
     Token PrevToken;