[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.

Author: cachemeifyoucan

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

@@ -402,12 +402,6 @@ 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: }