`-include a.h` probes `a.h.pch` and `a.h.gch`, if not found, falls back to
`a.h`. `.pch` is the preferred extension name. Probing .gch is supposed to
provide compatibility with build systems that do
```
clang -x c-header a.h -o out/a.h.gch
clang -include out/a.h -c a.c # out/a.h.gch is present while out/a.h is absent
```
(not sure what projects actually do this with Clang)
But it can often get in the way [^0][^1][^2] when GCC and Clang are mixed as the file
format is incompatible with GCC's. Let's deprecate .gch probing.
Some tests using `-include` are switched to `.pch`.
`test/PCH/pch-dir.c` shows the -Wdeprecated warning.
[^0]: https://discourse.llvm.org/t/how-to-have-clang-ignore-gch-directories/51835
[^1]: https://bugreports.qt.io/browse/QTCREATORBUG-22427
[^2]: https://gitlab.kitware.com/cmake/cmake/-/issues/22081
reparses an already-parsed translation unit. At the moment it's just a
convenience function, but we hope to use it for performance
optimizations.
llvm-svn: 108756
from a source file.
- This allows CIndex to avoid iterating over all the top-level decls when using
a PCH, which means we deserialize far fewer decls.
llvm-svn: 90559
