Support Clang Module

Author: CodaFi

lib/AST/Module.cpp

@@ -3448,8 +3448,7 @@ bool SourceFile::importsModuleAsWeakLinked(const ModuleDecl *module) const {
     importedModule->getImportedModules(reexportedModules,
                                        ModuleDecl::ImportFilterKind::Exported);
     for (const ImportedModule &reexportedModule : reexportedModules) {
-      if (!module->isNonSwiftModule() &&
-          module == reexportedModule.importedModule)
+      if (module == reexportedModule.importedModule)
         return true;
     }
   }

test/IRGen/Inputs/weaklinked_import_helper_clang.h

@@ -0,0 +1 @@
+extern void clang_fn(void);

test/IRGen/Inputs/weaklinked_import_helper_clang.modulemap

@@ -0,0 +1,4 @@
+module weaklinked_import_helper_clang {
+  header "weaklinked_import_helper_clang.h"
+  export *
+}

test/IRGen/weaklinked_import_peer_transitive.swift

@@ -5,11 +5,17 @@
 // RUN: echo '@_exported import weaklinked_import_helper' > %t/intermediate.swift
 // RUN: %target-swift-frontend -emit-module -emit-module-path %t/intermediate.swiftmodule -parse-as-library %t/intermediate.swift -I %t -enable-library-evolution
 //
-// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir | %FileCheck %s
+// RUN: echo '@_exported import weaklinked_import_helper_clang' > %t/intermediate_clang.swift
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/intermediate_clang.swiftmodule -parse-as-library %t/intermediate_clang.swift -I %t -enable-library-evolution -Xcc -fmodule-map-file=%S/Inputs/weaklinked_import_helper_clang.modulemap
+//
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -Xcc -fmodule-map-file=%S/Inputs/weaklinked_import_helper_clang.modulemap | %FileCheck %s
 
 // UNSUPPORTED: OS=windows-msvc
 
 @_weakLinked import intermediate
+@_weakLinked import intermediate_clang
 
 // CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper2fnyyF"()
 fn()
+// CHECK-DAG: declare extern_weak void @clang_fn()
+clang_fn()