Survive #pragma once from virtual file.

[tapaswenipathak]

Summary

Add check before marking file as a once-only file.

Ref: https://github.com/vgvassilev/clang/commit/728e1b3286.

Authored-by: Vassil Vassilev <[e-mail]>
Submitted-by: Tapasweni Pathak <[e-mail]>

[v.g.vassilev]

Can we write a test for this?

[aaron.ballman]

+1, this needs some test coverage for the changes. It should also have a release note to notify users of the fix.

clang/lib/Lex/Pragma.cpp

415–419

if (const auto *FE = getCurrentFileLexer()->getFileEntry())
  HeaderInfo.MarkFileIncludedOnce(FE);

[v.g.vassilev]

Historically, the patch was developed before the extended support of virtual files in Clang. Given that this is very hard to test and it looks like this is not needed on our end anymore. I'd propose to pause this for now.

[aaron.ballman]

In D128319#3615779, @v.g.vassilev wrote:

Historically, the patch was developed before the extended support of virtual files in Clang. Given that this is very hard to test and it looks like this is not needed on our end anymore. I'd propose to pause this for now.

That'd be fine by me -- I'd recommend explicitly abandoning the revision in Phabricator if you don't intend to work on it (that gets it off everyone's review plate).

clang/lib/Lex/Pragma.cpp

     return;
   }
 
-  // Get the current file lexer we're looking at.  Ignore _Pragma 'files' etc.
-  // Mark the file as a once-only file now.
-  HeaderInfo.MarkFileIncludeOnce(getCurrentFileLexer()->getFileEntry());
+  if (getCurrentFileLexer()->getFileEntry()) {
+    // Get the current file lexer we're looking at.  Ignore _Pragma 'files' etc.
+    // Mark the file as a once-only file now.
+    HeaderInfo.MarkFileIncludeOnce(getCurrentFileLexer()->getFileEntry());
+  }
 }
 
 void Preprocessor::HandlePragmaMark(Token &MarkTok) {