Merge pull request swiftlang#69309 from artemcm/DepScanOverlaysDirectOnly

[Dependency Scanning] On discovering cross-import overlays, do not add their discovered dependencies to the main module's direct dependencies

Author: artemcm

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -854,12 +854,22 @@ void ModuleDependencyScanner::discoverCrossImportOverlayDependencies(
   }
 
   // Update main module's dependencies to include these new overlays.
+  auto resolvedDummyDep =
+      *(cache.findDependency(dummyMainName, ModuleDependencyKind::SwiftSource)
+            .value());
   auto mainDep =
       *(cache.findDependency(mainModuleName, ModuleDependencyKind::SwiftSource)
             .value());
-  std::for_each(/* +1 to exclude dummy main*/ allModules.begin() + 1,
-                allModules.end(), [&](ModuleDependencyID dependencyID) {
-                  mainDep.addModuleDependency(dependencyID);
+  auto newOverlayDeps = resolvedDummyDep.getDirectModuleDependencies();
+  auto existingMainDeps = mainDep.getDirectModuleDependencies();
+  ModuleDependencyIDSet existingMainDepsSet(existingMainDeps.begin(),
+                                            existingMainDeps.end());
+  // Ensure we do not add cross-import overlay dependencies in case they
+  // were already explicitly imported
+  std::for_each(newOverlayDeps.begin(), newOverlayDeps.end(),
+                [&](ModuleDependencyID crossImportOverlayModID) {
+                  if (!existingMainDepsSet.count(crossImportOverlayModID))
+                    mainDep.addModuleDependency(crossImportOverlayModID);
                 });
   cache.updateDependency(
       {mainModuleName.str(), ModuleDependencyKind::SwiftSource}, mainDep);

test/ScanDependencies/Inputs/Swift/_cross_import_E.swiftinterface

@@ -3,4 +3,5 @@
 import Swift
 import E
 import SubE
+import X
 public func funcCrossImportE() {}

test/ScanDependencies/module_deps_cross_import_overlay.swift

@@ -24,4 +24,9 @@ import SubEWrapper
 // CHECK-DAG:   "swift": "_StringProcessing"
 // CHECK-DAG:   "swift": "_cross_import_E"
 // CHECK-DAG:   "clang": "_SwiftConcurrencyShims"
+// Ensure a transitive dependency via "_cross_import_E" is not a direct dep of main module
+// CHECK-NOT:   "clang": "X"
 // CHECK: ],
+
+// Ensure a transitive dependency via "_cross_import_E" is recorded in the graph still
+// CHECK:   "clang": "X"