[backported/clang-9][Preamble] Stop circular inclusion of main file when building preamblerelease_80-based

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https://reviews.llvm.org/D53866
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If a header file was processed for the second time, we could end up with
a wrong conditional stack and skipped ranges:

In the particular example, if the header guard is evaluated the second
time and it is decided to skip the conditional block, the corresponding
"#endif" is never seen since the preamble does not include it and we end
up in the Tok.is(tok::eof) case with a wrong conditional stack.

Detect the circular inclusion, emit a diagnostic and stop processing the
inclusion.

Fixes: QTCREATORBUG-20883
Change-Id: I02644ddb507db4033dd5c69920c8e10500f0121c
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/Lex/PPDirectives.cpp b/lib/Lex/PPDirectives.cpp
index d62a3513c7..b3cc9df60c 100644
--- a/lib/Lex/PPDirectives.cpp
+++ b/lib/Lex/PPDirectives.cpp
@@ -1855,6 +1855,18 @@ void Preprocessor::HandleIncludeDirective(SourceLocation HashLoc,
     return;
   }
 
+  // Check for circular inclusion of the main file.
+  // We can't generate a consistent preamble with regard to the conditional
+  // stack if the main file is included again as due to the preamble bounds
+  // some directives (e.g. #endif of a header guard) will never be seen.
+  // Since this will lead to confusing errors, avoid the inclusion.
+  if (File && PreambleConditionalStack.isRecording() &&
+      SourceMgr.translateFile(File) == SourceMgr.getMainFileID()) {
+    Diag(FilenameTok.getLocation(),
+         diag::err_pp_including_mainfile_in_preamble);
+    return;
+  }
+
   // Should we enter the source file? Set to false if either the source file is
   // known to have no effect beyond its effect on module visibility -- that is,
   // if it's got an include guard that is already defined or is a modular header