From 06c55d0463021f1a4ab2ce64e0b0bf2cf0f46c38 Mon Sep 17 00:00:00 2001
From: Artem Chikin <achikin@apple.com>
Date: Tue, 5 Aug 2025 15:24:06 -0700
Subject: [PATCH] [Dependency Scanning] Revert Swift overlay lookup using
 "visible" Clang modules only

We have identified scenarios where this is insufficient and compilation still relies on the presence of certain overlay modules this excludes. Reverting to prior lookup logic while we investigate.

Resolves rdar://157519278
---
 .../ModuleDependencyScanner.cpp               | 40 +++++++++++++++----
 ...dule_deps_swift_overlay_only_visible.swift |  1 +
 2 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/lib/DependencyScan/ModuleDependencyScanner.cpp b/lib/DependencyScan/ModuleDependencyScanner.cpp
index 3617a73294e18..858281081b0e3 100644
--- a/lib/DependencyScan/ModuleDependencyScanner.cpp
+++ b/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.
diff --git a/test/ScanDependencies/module_deps_swift_overlay_only_visible.swift b/test/ScanDependencies/module_deps_swift_overlay_only_visible.swift
index eff4edf747f5a..0d0c775c72aa4 100644
--- a/test/ScanDependencies/module_deps_swift_overlay_only_visible.swift
+++ b/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)