[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, 4 insertions, 1 deletions

diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
index 6b1fcac..ca37e06 100644
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -876,6 +876,7 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
 
     // Set the shared objects, these are reset when we finish processing the
     // file, otherwise the CompilerInstance will happily destroy them.
+    CI.setVirtualFileSystem(AST->getFileManager().getVirtualFileSystemPtr());
     CI.setFileManager(AST->getFileManagerPtr());
     CI.createSourceManager(CI.getFileManager());
     CI.getSourceManager().initializeForReplay(AST->getSourceManager());
@@ -966,7 +967,9 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
     return true;
   }
 
-  // Set up the file and source managers, if needed.
+  // Set up the file system, file and source managers, if needed.
+  if (!CI.hasVirtualFileSystem())
+    CI.createVirtualFileSystem();
   if (!CI.hasFileManager()) {
     if (!CI.createFileManager()) {
       return false;