Reapply "[NFC] Explicitly pass a VFS when creating DiagnosticsEngine (#115852)"

This reverts commit a1153cd6fedd4c906a9840987934ca4712e34cb2 with fixes
to lldb breakages.

Fixes https://github.com/llvm/llvm-project/issues/117145.

1 files changed, 4 insertions, 1 deletions

diff --git a/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp b/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp
index 638757a..d0b855f 100644
--- a/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp
+++ b/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp
@@ -22,6 +22,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/TargetParser/Host.h"
 using namespace clang;
 using namespace llvm::opt;
@@ -32,7 +33,9 @@ clang::createInvocation(ArrayRef<const char *> ArgList,
   assert(!ArgList.empty());
   auto Diags = Opts.Diags
                    ? std::move(Opts.Diags)
-                   : CompilerInstance::createDiagnostics(new DiagnosticOptions);
+                   : CompilerInstance::createDiagnostics(
+                         Opts.VFS ? *Opts.VFS : *llvm::vfs::getRealFileSystem(),
+                         new DiagnosticOptions);
 
   SmallVector<const char *, 16> Args(ArgList);