[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, 2 insertions, 1 deletions

diff --git a/clang/unittests/Driver/ToolChainTest.cpp b/clang/unittests/Driver/ToolChainTest.cpp
index 4fa2729..c1c5c96 100644
--- a/clang/unittests/Driver/ToolChainTest.cpp
+++ b/clang/unittests/Driver/ToolChainTest.cpp
@@ -579,7 +579,8 @@ TEST(CompilerInvocation, SplitSwarfSingleCrash) {
 
 TEST(ToolChainTest, UEFICallingConventionTest) {
   clang::CompilerInstance compiler;
-  compiler.createDiagnostics(*llvm::vfs::getRealFileSystem());
+  compiler.setVirtualFileSystem(llvm::vfs::getRealFileSystem());
+  compiler.createDiagnostics();
 
   std::string TrStr = "x86_64-unknown-uefi";
   llvm::Triple Tr(TrStr);