[Dependency Scanning] Revert Swift overlay lookup using "visible" Clang modules only

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -609,6 +609,25 @@ ModuleDependencyScanner::ModuleDependencyScanner(
         DependencyTracker, CAS, ActionCache, PrefixMapper.get(), Diagnostics));
 }
 
+/// Find all of the imported Clang modules starting with the given module name.
+static void findAllImportedClangModules(StringRef moduleName,
+                                        const ModuleDependenciesCache &cache,
+                                        std::vector<std::string> &allModules,
+                                        llvm::StringSet<> &knownModules) {
+  if (!knownModules.insert(moduleName).second)
+    return;
+  allModules.push_back(moduleName.str());
+  auto moduleID =
+      ModuleDependencyID{moduleName.str(), ModuleDependencyKind::Clang};
+  auto optionalDependencies = cache.findDependency(moduleID);
+  if (!optionalDependencies.has_value())
+    return;
+
+  for (const auto &dep : cache.getClangDependencies(moduleID))
+    findAllImportedClangModules(dep.ModuleName, cache, allModules,
+                                knownModules);
+}
+
 static std::set<ModuleDependencyID>
 collectBinarySwiftDeps(const ModuleDependenciesCache &cache) {
   std::set<ModuleDependencyID> binarySwiftModuleDepIDs;
@@ -1462,7 +1481,14 @@ void ModuleDependencyScanner::resolveSwiftOverlayDependenciesForModule(
     ModuleDependencyIDSetVector &swiftOverlayDependencies) {
   PrettyStackTraceStringAction trace(
       "Resolving Swift Overlay dependencies of module", moduleID.ModuleName);
-  auto visibleClangDependencies = cache.getVisibleClangModules(moduleID);
+  std::vector<std::string> allClangDependencies;
+  llvm::StringSet<> knownModules;
+
+  // Find all of the discovered Clang modules that this module depends on.
+  for (const auto &dep : cache.getClangDependencies(moduleID))
+    findAllImportedClangModules(dep.ModuleName, cache, allClangDependencies,
+                                knownModules);
+
   llvm::StringMap<SwiftModuleScannerQueryResult> swiftOverlayLookupResult;
   std::mutex lookupResultLock;
 
@@ -1492,9 +1518,9 @@ void ModuleDependencyScanner::resolveSwiftOverlayDependenciesForModule(
   };
 
   // Enque asynchronous lookup tasks
-  for (const auto &clangDep : visibleClangDependencies)
+  for (const auto &clangDep : allClangDependencies)
     ScanningThreadPool.async(scanForSwiftDependency,
-                             getModuleImportIdentifier(clangDep.getKey()));
+                             getModuleImportIdentifier(clangDep));
   ScanningThreadPool.wait();
 
   // Aggregate both previously-cached and freshly-scanned module results
@@ -1521,8 +1547,8 @@ void ModuleDependencyScanner::resolveSwiftOverlayDependenciesForModule(
             lookupResult.incompatibleCandidates, cache, std::nullopt);
     }
   };
-  for (const auto &clangDep : visibleClangDependencies)
-    recordResult(clangDep.getKey().str());
+  for (const auto &clangDep : allClangDependencies)
+    recordResult(clangDep);
 
   // C++ Interop requires additional handling
   bool lookupCxxStdLibOverlay = ScanCompilerInvocation.getLangOptions().EnableCXXInterop;
@@ -1543,8 +1569,8 @@ void ModuleDependencyScanner::resolveSwiftOverlayDependenciesForModule(
   }
 
   if (lookupCxxStdLibOverlay) {
-    for (const auto &clangDepNameEntry : visibleClangDependencies) {
-      auto clangDepName = clangDepNameEntry.getKey().str();
+    for (const auto &clangDepNameEntry : allClangDependencies) {
+      auto clangDepName = clangDepNameEntry;
       // If this Clang module is a part of the C++ stdlib, and we haven't
       // loaded the overlay for it so far, it is a split libc++ module (e.g.
       // std_vector). Load the CxxStdlib overlay explicitly.

test/ScanDependencies/module_deps_swift_overlay_only_visible.swift

@@ -1,3 +1,4 @@
+// REQUIRES: rdar157603647
 // RUN: %empty-directory(%t)
 // RUN: %empty-directory(%t/clang-module-cache)
 // RUN: %empty-directory(%t/swiftDeps)