Merge pull request #40418 from plotfi/main-extern-c

[cxx-interop] Fixing usage of ObjC Categories in C++-Interop mode.

Author: zoecarver

lib/ClangImporter/ImportDecl.cpp

@@ -9331,6 +9331,13 @@ ClangImporter::Implementation::importDeclContextOf(
   switch (context.getKind()) {
   case EffectiveClangContext::DeclContext: {
     auto dc = context.getAsDeclContext();
+
+    // For C++-Interop in cases where #ifdef __cplusplus surround an extern "C"
+    // you want to first check if the TU decl is the parent of this extern "C"
+    // decl (aka LinkageSpecDecl) and then proceed.
+    if (dc->getDeclKind() == clang::Decl::LinkageSpec)
+      dc = dc->getParent();
+
     if (dc->isTranslationUnit()) {
       if (auto *module = getClangModuleForDecl(decl))
         return module;

test/Interop/Cxx/extern-c/Inputs/extern-c.h

@@ -0,0 +1,11 @@
+@interface A
+@end
+
+extern "C"
+@interface A (CAT1)
+- (int)foo;
+@end
+
+@interface A (CAT2)
+- (int)bar;
+@end

test/Interop/Cxx/extern-c/Inputs/module.modulemap

@@ -0,0 +1,4 @@
+module ExternC {
+  header "extern-c.h"
+  requires cplusplus
+}

test/Interop/Cxx/extern-c/extern-c-objcxx-category.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-ide-test -print-module -module-to-print=ExternC -I %S/Inputs -source-filename=x -enable-cxx-interop -enable-objc-interop | %FileCheck %s
+
+// CHECK: class A {
+// CHECK-NEXT: }
+
+// CHECK: extension A {
+// CHECK-NEXT:   class func foo() -> Int32
+// CHECK-NEXT:   func foo() -> Int32
+// CHECK-NEXT: }
+
+// CHECK: extension A {
+// CHECK-NEXT:   class func bar() -> Int32
+// CHECK-NEXT:   func bar() -> Int32
+// CHECK-NEXT: }