[clang] Fix CAS initialization after upstream llvm#158381

With the early initialization of the VFS, the CAS is now being initialized too late. This PR initializes CAS along with the VFS so that the CAS filesystem can sit at the bottom.

Author: jansvoboda11

clang/include/clang/Frontend/CompilerInstance.h

@@ -530,6 +530,12 @@ class CompilerInstance : public ModuleLoader {
   /// Get the CAS, or create it using the configuration in CompilerInvocation.
   llvm::cas::ObjectStore &getOrCreateObjectStore();
   llvm::cas::ActionCache &getOrCreateActionCache();
+  std::shared_ptr<llvm::cas::ObjectStore> getObjectStorePtr() const {
+    return CAS;
+  }
+  std::shared_ptr<llvm::cas::ActionCache> getActionCachePtr() const {
+    return ActionCache;
+  }
 
   /// @}
   /// @name Source Manager

clang/lib/Frontend/CompileJobCache.cpp

@@ -296,7 +296,8 @@ std::optional<int> CompileJobCache::initialize(CompilerInstance &Clang) {
   if (!CacheCompileJob)
     return std::nullopt;
 
-  std::tie(CAS, Cache) = Clang.createCASDatabases();
+  CAS = Clang.getObjectStorePtr();
+  Cache = Clang.getActionCachePtr();
   if (!CAS || !Cache)
     return 1; // Exit with error!
 

clang/lib/Frontend/CompilerInstance.cpp

@@ -296,6 +296,10 @@ void CompilerInstance::createVirtualFileSystem(
   DiagnosticsEngine Diags(DiagnosticIDs::create(), DiagOpts, DC,
                           /*ShouldOwnClient=*/false);
 
+  std::tie(CAS, ActionCache) =
+      getInvocation().getCASOpts().getOrCreateDatabases(
+          Diags, /*CreateEmptyCASOnFailure=*/false);
+
   VFS = createVFSFromCompilerInvocation(getInvocation(), Diags,
                                         std::move(BaseFS), CAS);
   // FIXME: Should this go into createVFSFromCompilerInvocation?

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1536,9 +1536,6 @@ createBaseFS(const FileSystemOptions &FSOpts, const FrontendOptions &FEOpts,
              const CASOptions &CASOpts, DiagnosticsEngine &Diags,
              IntrusiveRefCntPtr<llvm::vfs::FileSystem> BaseFS,
              std::shared_ptr<llvm::cas::ObjectStore> OverrideCAS) {
-  if (!OverrideCAS)
-    return BaseFS;
-
   if (FSOpts.CASFileSystemRootID.empty() && FEOpts.CASIncludeTreeID.empty())
     return BaseFS;
 

clang/lib/Tooling/DependencyScanning/IncludeTreeActionController.cpp

@@ -282,10 +282,11 @@ void dependencies::addReversePrefixMappingFileSystem(
   llvm::PrefixMapper ReverseMapper;
   ReverseMapper.addInverseRange(PrefixMapper.getMappings());
   ReverseMapper.sort();
-  std::unique_ptr<llvm::vfs::FileSystem> FS =
+  IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS =
       llvm::vfs::createPrefixMappingFileSystem(
           std::move(ReverseMapper), &ScanInstance.getVirtualFileSystem());
 
+  ScanInstance.setVirtualFileSystem(FS);
   ScanInstance.getFileManager().setVirtualFileSystem(std::move(FS));
 }
 

clang/test/CAS/output-path-error.c

@@ -19,4 +19,4 @@
 // RUN: cat %t/output.txt | FileCheck %s --check-prefix=ERROR
 
 // CACHE-MISS: remark: compile job cache miss
-// ERROR: fatal error: CAS missing expected root-id
+// ERROR: fatal error: CAS filesystem cannot be initialized from root-id 'llvmcas://{{.*}}': cannot get reference to root FS