[clang][deps] Track VFS overlay files in file dependencies. (#167824)

rdar://164612831

Author: vsapsai

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

@@ -616,6 +616,9 @@ void ModuleDepCollectorPP::EndOfMainFile() {
   if (!MDC.ScanInstance.getPreprocessorOpts().ImplicitPCHInclude.empty())
     MDC.addFileDep(MDC.ScanInstance.getPreprocessorOpts().ImplicitPCHInclude);
 
+  for (StringRef VFS : MDC.ScanInstance.getHeaderSearchOpts().VFSOverlayFiles)
+    MDC.addFileDep(VFS);
+
   for (const Module *M :
        MDC.ScanInstance.getPreprocessor().getAffectingClangModules())
     if (!MDC.isPrebuiltModule(M))

clang/test/ClangScanDeps/modules-header-sharing.m

@@ -79,7 +79,8 @@
 // CHECK:                ],
 // CHECK:                "file-deps": [
 // CHECK-NEXT:             "[[PREFIX]]/tu.m",
-// CHECK-NEXT:             "[[PREFIX]]/shared/H.h"
+// CHECK-NEXT:             "[[PREFIX]]/shared/H.h",
+// CHECK-NEXT:             "[[PREFIX]]/overlay.json"
 // CHECK-NEXT:           ],
 // CHECK-NEXT:           "input-file": "[[PREFIX]]/tu.m"
 // CHECK-NEXT:         }