Test2

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -620,6 +620,23 @@ ModuleDependencyScanner::getMainModuleDependencyInfo(ModuleDecl *mainModule) {
       break;
     }
 
+    if (ScanASTContext.LangOpts.EnableCXXInterop) {
+      StringRef mainModuleName = mainModule->getName().str();
+      if (mainModuleName != CXX_MODULE_NAME)
+        mainDependencies.addModuleImport(CXX_MODULE_NAME, /* isExported */ false,
+                                         AccessLevel::Public,
+                                         &alreadyAddedModules);
+      if (llvm::none_of(llvm::ArrayRef<StringRef>{CXX_MODULE_NAME,
+                            ScanASTContext.Id_CxxStdlib.str(), "std"},
+                        [mainModuleName](StringRef Name) {
+                          return mainModuleName == Name;
+                        }))
+          mainDependencies.addModuleImport(ScanASTContext.Id_CxxStdlib.str(),
+                                           /* isExported */ false,
+                                           AccessLevel::Public,
+                                           &alreadyAddedModules);
+    }
+
     // Add any implicit module names.
     for (const auto &import : importInfo.AdditionalUnloadedImports) {
       mainDependencies.addModuleImport(

test/ScanDependencies/win-explicit-cxx-interop-cxxstdlib.swift

@@ -0,0 +1,43 @@
+// REQUIRES: OS=windows-msvc
+
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+// RUN: %target-swift-frontend -scan-dependencies -module-name NoCpp \
+// RUN:   -module-cache-path %t/clang-module-cache -disable-objc-interop \
+// RUN:   -cxx-interoperability-mode=default \
+// RUN:   %t/NoCpp.swift -o %t/NoCpp-deps.json -I %t 2>&1
+// RUN: %target-swift-frontend -scan-dependencies -module-name Cpp \
+// RUN:   -module-cache-path %t/clang-module-cache -disable-objc-interop \
+// RUN:   -cxx-interoperability-mode=default \
+// RUN:   %t/Cpp.swift -o %t/Cpp-deps.json -I %t 2>&1
+// RUN: %target-swift-frontend -scan-dependencies -module-name Crt \
+// RUN:   -module-cache-path %t/clang-module-cache -disable-objc-interop \
+// RUN:   -cxx-interoperability-mode=default \
+// RUN:   %t/Crt.swift -o %t/Crt-deps.json -I %t 2>&1
+// RUN: %FileCheck %s --check-prefix=NOCPP < %t/NoCpp-deps.json
+// RUN: %FileCheck %s --check-prefix=CPP < %t/Cpp-deps.json
+// RUN: %FileCheck %s --check-prefix=CRT < %t/Crt-deps.json
+
+// NOCPP:      "mainModuleName": "NoCpp"
+// NOCPP:      "linkName": "swiftCxxStdlib",
+// NOCPP-NEXT: "isStatic": true,
+
+// CPP:        "mainModuleName": "Cpp"
+// CPP:        "linkName": "swiftCxxStdlib",
+// CPP-NEXT:   "isStatic": true,
+
+// CRT:        "mainModuleName": "Crt"
+// CRT:        "linkName": "swiftCxxStdlib",
+// CRT-NEXT:   "isStatic": true,
+
+//--- NoCpp.swift
+// Empty
+
+//--- Cpp.swift
+import CxxStdlib
+
+//--- Crt.swift
+import CRT
+
+
+