[clang] Don't silently inherit the VFS from FileManager (#164323)

Since #158381 the
`CompilerInstance` is aware of the VFS and co-owns it. To reduce scope
of that PR, the VFS was being inherited from the `FileManager` during
`setFileManager()` if it wasn't configured before. However, the
implementation of that setter was buggy. This PR fixes the bug, and
moves us closer to the long-term goal of `CompilerInstance` requiring
the VFS to be configured explicitly and owned by the instance.

Author: jansvoboda11

clang-tools-extra/clang-include-fixer/IncludeFixer.cpp

@@ -90,6 +90,7 @@ bool IncludeFixerActionFactory::runInvocation(
 
   // Set up Clang.
   CompilerInstance Compiler(std::move(Invocation), std::move(PCHContainerOps));
+  Compiler.setVirtualFileSystem(Files->getVirtualFileSystemPtr());
   Compiler.setFileManager(Files);
 
   // Create the compiler's actual diagnostics engine. We want to drop all

clang/include/clang/Frontend/ASTUnit.h

@@ -499,6 +499,11 @@ class ASTUnit {
     return *PPOpts;
   }
 
+  IntrusiveRefCntPtr<llvm::vfs::FileSystem> getVirtualFileSystemPtr() {
+    // FIXME: Don't defer VFS ownership to the FileManager.
+    return FileMgr->getVirtualFileSystemPtr();
+  }
+
   const FileManager &getFileManager() const { return *FileMgr; }
   FileManager &getFileManager() { return *FileMgr; }
   IntrusiveRefCntPtr<FileManager> getFileManagerPtr() { return FileMgr; }

clang/include/clang/Frontend/CompilerInstance.h

@@ -460,7 +460,7 @@ class CompilerInstance : public ModuleLoader {
     FileMgr.resetWithoutRelease();
   }
 
-  /// Replace the current file manager and virtual file system.
+  /// Replace the current file manager.
   void setFileManager(IntrusiveRefCntPtr<FileManager> Value);
 
   /// @}

clang/lib/Frontend/ASTUnit.cpp

@@ -1651,6 +1651,7 @@ ASTUnit *ASTUnit::LoadFromCompilerInvocationAction(
   AST->Reader = nullptr;
 
   // Create a file manager object to provide access to and cache the filesystem.
+  Clang->setVirtualFileSystem(AST->getVirtualFileSystemPtr());
   Clang->setFileManager(AST->getFileManagerPtr());
 
   // Create the source manager.
@@ -2290,6 +2291,7 @@ void ASTUnit::CodeComplete(
          "IR inputs not support here!");
 
   // Use the source and file managers that we were given.
+  Clang->setVirtualFileSystem(FileMgr->getVirtualFileSystemPtr());
   Clang->setFileManager(FileMgr);
   Clang->setSourceManager(SourceMgr);
 

clang/lib/Frontend/CompilerInstance.cpp

@@ -160,8 +160,6 @@ bool CompilerInstance::createTarget() {
 }
 
 void CompilerInstance::setFileManager(IntrusiveRefCntPtr<FileManager> Value) {
-  if (!hasVirtualFileSystem())
-    setVirtualFileSystem(Value->getVirtualFileSystemPtr());
   assert(Value == nullptr ||
          getVirtualFileSystemPtr() == Value->getVirtualFileSystemPtr());
   FileMgr = std::move(Value);

clang/lib/Frontend/FrontendAction.cpp

@@ -945,6 +945,7 @@ 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->getVirtualFileSystemPtr());
     CI.setFileManager(AST->getFileManagerPtr());
     CI.setSourceManager(AST->getSourceManagerPtr());
     CI.setPreprocessor(AST->getPreprocessorPtr());

clang/lib/Frontend/PrecompiledPreamble.cpp

@@ -479,16 +479,12 @@ llvm::ErrorOr<PrecompiledPreamble> PrecompiledPreamble::Build(
   Diagnostics->Reset();
   ProcessWarningOptions(*Diagnostics, Clang->getDiagnosticOpts(), *VFS);
 
-  VFS = createVFSFromCompilerInvocation(Clang->getInvocation(), *Diagnostics,
-                                        VFS);
-
   // Create a file manager object to provide access to and cache the filesystem.
-  Clang->setFileManager(
-      llvm::makeIntrusiveRefCnt<FileManager>(Clang->getFileSystemOpts(), VFS));
+  Clang->createVirtualFileSystem(VFS);
+  Clang->createFileManager();
 
   // Create the source manager.
-  Clang->setSourceManager(llvm::makeIntrusiveRefCnt<SourceManager>(
-      *Diagnostics, Clang->getFileManager()));
+  Clang->createSourceManager();
 
   auto PreambleDepCollector = std::make_shared<PreambleDependencyCollector>();
   Clang->addDependencyCollector(PreambleDepCollector);

clang/lib/StaticAnalyzer/Frontend/ModelInjector.cpp

@@ -93,6 +93,7 @@ void ModelInjector::onBodySynthesis(const NamedDecl *D) {
 
   // The instance wants to take ownership, however DisableFree frontend option
   // is set to true to avoid double free issues
+  Instance.setVirtualFileSystem(CI.getVirtualFileSystemPtr());
   Instance.setFileManager(CI.getFileManagerPtr());
   Instance.setSourceManager(SM);
   Instance.setPreprocessor(CI.getPreprocessorPtr());

clang/lib/Tooling/Tooling.cpp

@@ -446,6 +446,7 @@ bool FrontendActionFactory::runInvocation(
     DiagnosticConsumer *DiagConsumer) {
   // Create a compiler instance to handle the actual work.
   CompilerInstance Compiler(std::move(Invocation), std::move(PCHContainerOps));
+  Compiler.setVirtualFileSystem(Files->getVirtualFileSystemPtr());
   Compiler.setFileManager(Files);
 
   // The FrontendAction can have lifetime requirements for Compiler or its

clang/tools/clang-installapi/ClangInstallAPI.cpp

@@ -114,6 +114,7 @@ static bool run(ArrayRef<const char *> Args, const char *ProgName) {
 
   // Set up compilation.
   std::unique_ptr<CompilerInstance> CI(new CompilerInstance());
+  CI->setVirtualFileSystem(FM->getVirtualFileSystemPtr());
   CI->setFileManager(FM);
   CI->createDiagnostics();
   if (!CI->hasDiagnostics())