[Dependency Scanning] Remove 'overlaySharedFilesystemCacheForCompilation' from the scanner. It overlays a non-thread-safe filesystem on shared compilation instances and is no longer valid with parallel scanning.

Author: artemcm

include/swift/AST/ModuleDependencies.h

@@ -915,10 +915,6 @@ class SwiftDependencyScanningService {
     return Mapper->mapToString(Path);
   }
 
-  /// Wrap the filesystem on the specified `CompilerInstance` with a
-  /// caching `DependencyScanningWorkerFilesystem`
-  void overlaySharedFilesystemCacheForCompilation(CompilerInstance &Instance);
-
   /// Setup caching service.
   bool setupCachingDependencyScanningService(CompilerInstance &Instance);
 private:

lib/AST/ModuleDependencies.cpp

@@ -480,17 +480,6 @@ SwiftDependencyTracker::createTreeFromDependencies() {
       });
 }
 
-void SwiftDependencyScanningService::overlaySharedFilesystemCacheForCompilation(
-    CompilerInstance &Instance) {
-  auto existingFS = Instance.getSourceMgr().getFileSystem();
-  llvm::IntrusiveRefCntPtr<
-      clang::tooling::dependencies::DependencyScanningWorkerFilesystem>
-      depFS =
-          new clang::tooling::dependencies::DependencyScanningWorkerFilesystem(
-              getSharedFilesystemCache(), existingFS);
-  Instance.getSourceMgr().setFileSystem(depFS);
-}
-
 bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
     CompilerInstance &Instance) {
   if (!Instance.getInvocation().getFrontendOptions().EnableCaching)

lib/DependencyScan/ScanDependencies.cpp

@@ -1448,8 +1448,6 @@ bool swift::dependencies::scanDependencies(CompilerInstance &instance) {
   if (opts.ReuseDependencyScannerCache)
     deserializeDependencyCache(instance, service);
 
-  // Wrap the filesystem with a caching `DependencyScanningWorkerFilesystem`
-  service.overlaySharedFilesystemCacheForCompilation(instance);
   if (service.setupCachingDependencyScanningService(instance))
     return true;
 
@@ -1520,7 +1518,6 @@ bool swift::dependencies::batchScanDependencies(
   // we have created
 
   SwiftDependencyScanningService singleUseService;
-  singleUseService.overlaySharedFilesystemCacheForCompilation(instance);
   if (singleUseService.setupCachingDependencyScanningService(instance))
     return true;