[clang] Initialize the file system explicitly (#158381)

This PR is a part of the effort to make the VFS used in the compiler
more explicit and consistent.

Instead of creating the VFS deep within the compiler (in
`CompilerInstance::createFileManager()`), clients are now required to
explicitly call `CompilerInstance::createVirtualFileSystem()` and
provide the base VFS from the outside.

This PR also helps in breaking up the dependency cycle where creating a
properly configured `DiagnosticsEngine` requires a properly configured
VFS, but creating properly configuring a VFS requires the
`DiagnosticsEngine`.

Both `CompilerInstance::create{FileManager,Diagnostics}()` now just use
the VFS already in `CompilerInstance` instead of taking one as a
parameter, making the VFS consistent across the instance sub-object.

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/Frontend/ChainedIncludesSource.cpp b/clang/lib/Frontend/ChainedIncludesSource.cpp
index 013814a7..82249f8 100644
--- a/clang/lib/Frontend/ChainedIncludesSource.cpp
+++ b/clang/lib/Frontend/ChainedIncludesSource.cpp
@@ -124,6 +124,7 @@ clang::createChainedIncludesSource(CompilerInstance &CI,
 
     auto Clang = std::make_unique<CompilerInstance>(
         std::move(CInvok), CI.getPCHContainerOperations());
+    Clang->createVirtualFileSystem();
     Clang->setDiagnostics(Diags);
     Clang->setTarget(TargetInfo::CreateTargetInfo(
         Clang->getDiagnostics(), Clang->getInvocation().getTargetOpts()));