[Explicit Module Builds] Propagate the C++ Interop mode to interface sub-invocations and dependency scanner

Author: artemcm

include/swift/Serialization/SerializedModuleLoader.h

@@ -171,8 +171,8 @@ class SerializedModuleLoaderBase : public ModuleLoader {
     std::string headerImport;
   };
 
-  static BinaryModuleImports
-  getImportsOfModule(const ModuleFileSharedCore &loadedModule,
+  llvm::ErrorOr<BinaryModuleImports>
+  getImportsOfModule(Twine modulePath,
                      ModuleLoadingBehavior transitiveBehavior,
                      StringRef packageName, bool isTestableImport);
 

lib/Frontend/CompilerInvocation.cpp

@@ -506,6 +506,9 @@ validateCxxInteropCompatibilityMode(StringRef mode) {
   // Swift 5 is the default language version.
   if (mode == "swift-5.9")
     return {CxxCompatMode::enabled, version::Version({5})};
+  // Note: If this is updated, corresponding code in
+  // InterfaceSubContextDelegateImpl::InterfaceSubContextDelegateImpl needs
+  // to be updated also.
   return {CxxCompatMode::invalid, {}};
 }
 

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1971,6 +1971,31 @@ InterfaceSubContextDelegateImpl::InterfaceSubContextDelegateImpl(
     GenericArgs.push_back("-blocklist-file");
     GenericArgs.push_back(blocklist);
   }
+
+  // For now, we only inherit the C++ interoperability mode in
+  // Explicit Module Builds.
+  if (langOpts.EnableCXXInterop &&
+      (frontendOpts.DisableImplicitModules ||
+       LoaderOpts.requestedAction ==
+           FrontendOptions::ActionType::ScanDependencies)) {
+    // Modelled after a reverse of validateCxxInteropCompatibilityMode
+    genericSubInvocation.getLangOptions().EnableCXXInterop = true;
+    genericSubInvocation.getLangOptions().cxxInteropCompatVersion =
+        langOpts.cxxInteropCompatVersion;
+    std::string compatVersion;
+    if (langOpts.cxxInteropCompatVersion.empty())
+      compatVersion = "default";
+    else if (langOpts.cxxInteropCompatVersion[0] == 5)
+      compatVersion = "swift-5.9";
+    else if (langOpts.cxxInteropCompatVersion[0] ==
+             version::getUpcomingCxxInteropCompatVersion())
+      compatVersion = "upcoming-swift";
+    else // TODO: This may need to be updated once more versions are added
+      compatVersion = "default";
+
+    GenericArgs.push_back(
+        ArgSaver.save("-cxx-interoperability-mode=" + compatVersion));
+  }
 }
 
 /// Calculate an output filename in \p genericSubInvocation's cache path that

lib/Serialization/SerializedModuleLoader.cpp

@@ -422,6 +422,13 @@ SerializedModuleLoaderBase::getImportsOfModule(
     if (dotPos != std::string::npos)
       moduleName = moduleName.slice(0, dotPos);
 
+    // Reverse rewrite of user-specified C++ standard
+    // library module name to one used in the modulemap.
+    // TODO: If we are going to do this for more than this module,
+    // we will need a centralized system for doing module import name remap.
+    if (moduleName == Ctx.Id_CxxStdlib.str())
+      moduleName = "std";
+
     importedModuleNames.insert(moduleName);
   }