[CAS][DepScan] Fix depscan by module name using CAS

Fix clang module depscan by module name. The file system in the
SourceManager is already set during initialization with an in-memory
overlay on top of the DependencyScanningCASFileSystem. Do not overwrite
it back to the underlying filesystem that will fail the look up for the
fake module.

(cherry picked from commit 4b015ce)

Author: cachemeifyoucan

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

@@ -401,12 +401,6 @@ class DependencyScanningAction : public tooling::ToolAction {
     }
     // CAS Implementation.
     if (DepCASFS) {
-      // Support for virtual file system overlays on top of the caching
-      // filesystem.
-      FileMgr->setVirtualFileSystem(createVFSFromCompilerInvocation(
-          ScanInstance.getInvocation(), ScanInstance.getDiagnostics(),
-          DepCASFS));
-
       llvm::IntrusiveRefCntPtr<DependencyScanningCASFilesystem> LocalDepCASFS =
           DepCASFS;
       ScanInstance.getPreprocessorOpts().DependencyDirectivesForFile =

clang/test/ClangScanDeps/modules-cas-full-by-mod-name.c

@@ -0,0 +1,90 @@
+// UNSUPPORTED: target=powerpc64-ibm-aix{{.*}}
+// REQUIRES: ondisk_cas
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+//--- module.modulemap
+module root { header "root.h" }
+module direct { header "direct.h" }
+module transitive { header "transitive.h" }
+//--- root.h
+#include "direct.h"
+#include "root/textual.h"
+//--- direct.h
+#include "transitive.h"
+//--- transitive.h
+// empty
+
+//--- root/textual.h
+// This is here to verify that the "root" directory doesn't clash with name of
+// the "root" module.
+
+//--- cdb.json.template
+[{
+  "file": "",
+  "directory": "DIR",
+  "command": "clang -fmodules -fmodules-cache-path=DIR/cache -I DIR -x c"
+}]
+
+// RUN: sed "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
+// RUN: clang-scan-deps -compilation-database %t/cdb.json \
+// RUN:   -cas-path %t/cas -action-cache-path %t/cache \
+// RUN:   -format experimental-full -module-name=root > %t/result.json
+// RUN: cat %t/result.json | sed 's:\\\\\?:/:g' | FileCheck -DPREFIX=%/t %s
+
+// CHECK:      {
+// CHECK-NEXT:   "modules": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "casfs-root-id": "[[LEFT_ROOT_ID:llvmcas://[[:xdigit:]]+]]"
+// CHECK-NEXT:       "clang-module-deps": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "context-hash": "{{.*}}",
+// CHECK-NEXT:           "module-name": "transitive"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/direct.h"
+// CHECK-NEXT:         "[[PREFIX]]/module.modulemap"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "name": "direct"
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "casfs-root-id": "[[LEFT_ROOT_ID:llvmcas://[[:xdigit:]]+]]"
+// CHECK-NEXT:       "clang-module-deps": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "context-hash": "{{.*}}",
+// CHECK-NEXT:           "module-name": "direct"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/module.modulemap"
+// CHECK-NEXT:         "[[PREFIX]]/root.h"
+// CHECK-NEXT:         "[[PREFIX]]/root/textual.h"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "name": "root"
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "casfs-root-id": "[[LEFT_ROOT_ID:llvmcas://[[:xdigit:]]+]]"
+// CHECK-NEXT:       "clang-module-deps": [],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/module.modulemap"
+// CHECK-NEXT:         "[[PREFIX]]/transitive.h"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "name": "transitive"
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ],
+// CHECK-NEXT:   "translation-units": []
+// CHECK-NEXT: }