[PATCH] D123398: [VFS] RedirectingFileSystem only replace path if not already mapped

[Ben Barham via Phabricator via cfe-commits]

bnbarham created this revision.
bnbarham added reviewers: dexonsmith, keith, JDevlieghere, vsapsai, sammccall.
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bnbarham requested review of this revision.
Herald added projects: clang, LLVM.
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If the `ExternalFS` has already remapped to an external path then
`RedirectingFileSystem` should not change it to the originally provided
path. This fixes the original path always being used if multiple VFS
overlays were provided and the path wasn't found in the highest (ie.
first in the chain).

For now this is accomplished through the use of a new
`ExposesExternalVFSPath` field on `vfs::Status`. This flag is true when
the `Status` has an external path that's different from its virtual
path, ie. the contained path is the external path. See the plan in
`FileManager::getFileRef` for where this is going - eventually we won't
need `IsVFSMapped` any more and all returned paths should be virtual.

Resolves rdar://90578880 and llvm-project#53306.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D123398

Files:
  clang/lib/Basic/FileManager.cpp
  clang/test/VFS/external-names-multi-overlay.c
  llvm/include/llvm/Support/VirtualFileSystem.h
  llvm/lib/Support/VirtualFileSystem.cpp
  llvm/unittests/Support/VirtualFileSystemTest.cpp

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