[clang][deps] Respect VFS overlays in canonical preprocessing mode

[jansvoboda11]

Summary

The -ivfsoverlay flag was only being respected when the scanner was instructed to minimize the inputs. This patch respects that flag even in canonical preprocessing mode.

Depends on D135414.

[jansvoboda11]

Add forgotten hunk.

[Bigcheese]

Ah, I hit the same thing recently, thanks.

lgtm.

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

bool runInvocation(std::shared_ptr<CompilerInvocation> Invocation,
     ScanInstance.getPreprocessorOpts().AllowPCHWithDifferentModulesCachePath =
         true;
 
     ScanInstance.getFrontendOpts().GenerateGlobalModuleIndex = false;
     ScanInstance.getFrontendOpts().UseGlobalModuleIndex = false;
     ScanInstance.getFrontendOpts().ModulesShareFileManager = false;
 
     ScanInstance.setFileManager(FileMgr);
+    // Support for virtual file system overlays.
+    FileMgr->setVirtualFileSystem(createVFSFromCompilerInvocation(
+        ScanInstance.getInvocation(), ScanInstance.getDiagnostics(),
+        FileMgr->getVirtualFileSystemPtr()));
+
     ScanInstance.createSourceManager(*FileMgr);
 
     llvm::StringSet<> PrebuiltModulesInputFiles;
     // Store the list of prebuilt module files into header search options. This
     // will prevent the implicit build to create duplicate modules and will
     // force reuse of the existing prebuilt module files instead.
     if (!ScanInstance.getPreprocessorOpts().ImplicitPCHInclude.empty())
       visitPrebuiltModule(
           ScanInstance.getPreprocessorOpts().ImplicitPCHInclude, ScanInstance,
           ScanInstance.getHeaderSearchOpts().PrebuiltModuleFiles,
           PrebuiltModulesInputFiles, /*VisitInputFiles=*/DepFS != nullptr);
 
     // Use the dependency scanning optimized file system if requested to do so.
     if (DepFS) {
-      // Support for virtual file system overlays on top of the caching
-      // filesystem.
-      FileMgr->setVirtualFileSystem(createVFSFromCompilerInvocation(
-          ScanInstance.getInvocation(), ScanInstance.getDiagnostics(),
-          FileMgr->getVirtualFileSystemPtr()));
-
       llvm::IntrusiveRefCntPtr<DependencyScanningWorkerFilesystem> LocalDepFS =
           DepFS;
       ScanInstance.getPreprocessorOpts().DependencyDirectivesForFile =
           [LocalDepFS = std::move(LocalDepFS)](FileEntryRef File)
           -> Optional<ArrayRef<dependency_directives_scan::Directive>> {
         if (llvm::ErrorOr<EntryRef> Entry =
                 LocalDepFS->getOrCreateFileSystemEntry(File.getName()))
           return Entry->getDirectiveTokens();

clang/test/ClangScanDeps/vfsoverlay.cpp

 // RUN: rm -rf %t.dir
 // RUN: rm -rf %t.cdb
 // RUN: mkdir -p %t.dir
 // RUN: cp %s %t.dir/vfsoverlay_input.cpp
 // RUN: cp %s %t.dir/vfsoverlay_input_clangcl.cpp
 // RUN: sed -e "s|DIR|%/t.dir|g" %S/Inputs/vfsoverlay.yaml > %t.dir/vfsoverlay.yaml
 // RUN: mkdir %t.dir/Inputs
 // RUN: cp %S/Inputs/header.h %t.dir/Inputs/header.h
 // RUN: sed -e "s|DIR|%/t.dir|g" %S/Inputs/vfsoverlay_cdb.json > %t.cdb
 //
-// RUN: clang-scan-deps -compilation-database %t.cdb -j 1 | \
-// RUN:   FileCheck %s
+// RUN: clang-scan-deps -compilation-database %t.cdb -mode preprocess-dependency-directives -j 1 | FileCheck %s
+// RUN: clang-scan-deps -compilation-database %t.cdb -mode preprocess                       -j 1 | FileCheck %s
 
 #include "not_real.h"
 
 // CHECK: vfsoverlay_input.o
 // CHECK-NEXT: vfsoverlay_input.cpp
 // CHECK-NEXT: Inputs{{/|\\}}header.h
 
 // CHECK: vfsoverlay_input_clangcl.o
 // CHECK-NEXT: vfsoverlay_input_clangcl.cpp
 // CHECK-NEXT: Inputs{{/|\\}}header.h