[PATCH] D37474: [PCH] Allow VFS to be used for tests that generate PCH files

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov added a comment.

Could we fix this in tests instead by providing an overlay over `RealFS` there instead of doing that in `ASTUnit`?

If I'm passing `vfs::FileSystem`, I specifically **do not want** any file accesses to silently go through `RealFS`, ignoring the `vfs::FileSystem` that I passed.

We do overlays in `clangd` and we also have a `vfs::FileSystem` implementation that only reads certain `WhitelistedDirs` from `RealFS` to ensure we don't read other files from `RealFS`.
See https://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/unittests/clangd/ClangdTests.cpp;312537$34.


https://reviews.llvm.org/D37474