ASTReader: Bypass overridden files when reading PCHs

If contents of a file that is part of a PCM are overridden when reading
it, but weren't overridden when the PCM was being built, the ASTReader
will emit an error.  Now it creates a separate FileEntry for recovery,
bypassing the overridden content instead of discarding it.  The
pre-existing testcase clang/test/PCH/remap-file-from-pch.cpp confirms
that the new recovery method works correctly.

This resolves a long-standing FIXME to avoid hypothetically invalidating
another precompiled module that's already using the overridden contents.

This also removes ContentCache-related API that would be unsafe to use
across `CompilerInstance`s in an implicit modules build.  This helps to
unblock us sinking it from SourceManager into FileManager in the future,
which would allow us to delete `InMemoryModuleCache`.

https://reviews.llvm.org/D66710

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@370546 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 3 deletions

diff --git a/include/clang/Basic/SourceManager.h b/include/clang/Basic/SourceManager.h
index 3176f44b2b..3185ca0f4a 100644
--- a/include/clang/Basic/SourceManager.h
+++ b/include/clang/Basic/SourceManager.h
@@ -952,11 +952,12 @@ public:
     return false;
   }
 
-  /// Disable overridding the contents of a file, previously enabled
-  /// with #overrideFileContents.
+  /// Bypass the overridden contents of a file.  This creates a new FileEntry
+  /// and initializes the content cache for it.  Returns nullptr if there is no
+  /// such file in the filesystem.
   ///
   /// This should be called before parsing has begun.
-  void disableFileContentsOverride(const FileEntry *File);
+  const FileEntry *bypassFileContentsOverride(const FileEntry &File);
 
   /// Specify that a file is transient.
   void setFileIsTransient(const FileEntry *SourceFile);