Merge pull request #77966 from cachemeifyoucan/eng/PR-139233781

[ScanDependency] Fix a regression caused by rewrite in #76700

Author: cachemeifyoucan

lib/DependencyScan/ScanDependencies.cpp

@@ -451,6 +451,11 @@ class ExplicitModuleDependencyResolver {
   }
 
   void pruneUnusedVFSOverlay() {
+    // Pruning of unused VFS overlay options for Clang dependencies is performed
+    // by the Clang dependency scanner.
+    if (moduleID.Kind == ModuleDependencyKind::Clang)
+      return;
+
     std::vector<std::string> resolvedCommandLine;
     size_t skip = 0;
     for (auto it = commandline.begin(), end = commandline.end();

test/ScanDependencies/preserve_used_vfs.swift

@@ -65,3 +65,10 @@ import F
 
 /// --------Clang module F
 // CHECK-LABEL: "modulePath": "{{.*}}{{/|\\}}F-{{.*}}.pcm",
+// CHECK: "commandLine": [
+// CHECK: "-vfsoverlay",
+// CHECK-NEXT: "{{.*}}{{/|\\}}preserve_used_vfs.swift.tmp{{/|\\}}overlay.yaml",
+// CHECK: "-ivfsoverlay",
+// CHECK-NEXT: "-Xcc",
+// CHECK-NEXT: "{{.*}}{{/|\\}}preserve_used_vfs.swift.tmp{{/|\\}}overlay.yaml",
+// CHECK: ],