[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, 5 insertions, 2 deletions

diff --git a/clang/lib/Interpreter/Interpreter.cpp b/clang/lib/Interpreter/Interpreter.cpp
index 07c170a..9cc1c45 100644
--- a/clang/lib/Interpreter/Interpreter.cpp
+++ b/clang/lib/Interpreter/Interpreter.cpp
@@ -107,8 +107,10 @@ CreateCI(const llvm::opt::ArgStringList &Argv) {
     Clang->getHeaderSearchOpts().ResourceDir =
         CompilerInvocation::GetResourcesPath(Argv[0], nullptr);
 
+  Clang->createVirtualFileSystem();
+
   // Create the actual diagnostics engine.
-  Clang->createDiagnostics(*llvm::vfs::getRealFileSystem());
+  Clang->createDiagnostics();
   if (!Clang->hasDiagnostics())
     return llvm::createStringError(llvm::errc::not_supported,
                                    "Initialization failed. "
@@ -475,7 +477,8 @@ Interpreter::createWithCUDA(std::unique_ptr<CompilerInstance> CI,
       std::make_unique<llvm::vfs::OverlayFileSystem>(
           llvm::vfs::getRealFileSystem());
   OverlayVFS->pushOverlay(IMVFS);
-  CI->createFileManager(OverlayVFS);
+  CI->createVirtualFileSystem(OverlayVFS);
+  CI->createFileManager();
 
   llvm::Expected<std::unique_ptr<Interpreter>> InterpOrErr =
       Interpreter::create(std::move(CI));