I’m working on an application that requires the use of
a pre compiled header (PCH) but we don’t want the header to be
distributed as a separate file. I want to discuss my approach for suggestions and
the solution I found as I believe it uncovered a corner case in the PCH
The chosen approach is to include the header as an app
resource and load it when compiling a file. One problem is that the location of
the header file used to generate the PCH is stored in the PCH and used to
validate the PCH. The PCH file won’t be present on disk causing a
compilation error if it’s used. I read the PHC documentation and neither
PCH flavor (standard or relocatable) helps in this case. To go around the file
check I generated the PCH by streaming the header file to clang. This adds the
content in the PCH as a buffer blob instead of a file. The command line I used
to build the PCH is something like this: clang -cc1 -x some_language -triple=some_target
-emit-pch -o $myHeader.pch < myHeader.h. The x and triple switches need to
match whatever is used by clang during actual source code compilation.
When using the PCH to compile a file I found a problem with ReadPredefinesBuffer()
(PCHReader.cpp/ASTReader.cpp). This function performs some validation on the
PCH and sets the preprocessor (PP) predefines to what’s in the PCH. The
problem is that the function assumes that the PCH was created from a file. For PCHs
from streamed sources the OriginalFileName string is empty causing problems in NormalizeDashIncludePath()
and the assert/check following that call. I placed a check around the top block
of code in ReadPredefinesBuffer() where if OriginalFileName is not empty the
original code is executed but it is then the ‘Left’ string is set
to the PP predefines from the PCH.
My questions are:
1) Is there a better approach I can follow?
2) Is generating a PCH from an streamed file a valid usage
3) If so, is it correct for ReadPredefinesBuffer() to assume
that OriginalFileName is never empty?
4) If not then is anyone interested in checking-in the fix I
made to allow compilation from PCH generated from a streamed file? I can also update
the documentation to include this usage model.