clang PCH problems

[TTimo]

I am using a clang based project on Linux that uses PCH and I see a variety of errors:

Error while processing [.cpp] 
error: exception handling was disabled in PCH file but is currently enabled
error: PCH file was compiled for the target 'x86_64-pc-linux-gnu' but the current translation unit is being compiled for target 'x86_64-unknown-linux-gnu'

And this also:

error: PCH file uses an older PCH format that is no longer supported

(this one happens on an older version of the source that requires clang 3.5)

[pron]

See similar issue and solution in another tool: facebook/infer#96

[mlangkabel]

Thank you for the pointer!

[pron]

I'm afraid this has now become a blocking bug for me, and I can no longer use SourceTrail (not conveniently, at least).

[egraether]

@pron Thanks, we will look into it!

How did you work around this issue so far? And why did it become blocking now?

[pron]

I've used another configuration of the build without precompiled headers, and it's becoming inconvenient, as now it exists only to satisfy Sourcetrail. I can probably hang on to it for a while more.

[mlangkabel]

Quick update: We are currently looking into making PCH support available for the "empty c/c++" Source Groups.

Getting PCH support ready for Source Groups that are based on a compilation database will be tricky, because the flags used for generating the PCH file need to match the flags used for the actual translation units (as @TTimo pointed out in the original submission) and in theory every translation unit of a compilation database can have a different set of arguments.

[mlangkabel]

Implemented PCH support for Empty C Source Group and Empty C++ Source Group with Sourcetrail 2019.3.6. Enabling PCH support for Source Groups that depend on a Compilation Database will be a different story, but sill may be part of the next release.

[egraether]

Added PCH support to CDB Source Groups with 2019.3.18