Support applying macros to imported-as-member declarations

lib/ClangImporter/ImportDecl.cpp

@@ -9669,6 +9669,13 @@ bool ClangImporter::Implementation::addMemberAndAlternatesToExtension(
       if (!isa<AccessorDecl>(alternate))
         ext->addMember(alternate);
   }
+
+  member->visitAuxiliaryDecls([&](Decl *aux) {
+    if (auto auxValue = dyn_cast<ValueDecl>(aux)) {
+      ext->addMember(auxValue);
+    }
+  });
+
   return true;
 }
 
@@ -9741,6 +9748,16 @@ void ClangImporter::Implementation::insertMembersAndAlternates(
       }
     }
 
+    // If there are auxiliary declarations (e.g., produced by macros), load
+    // those.
+    member->visitAuxiliaryDecls([&](Decl *aux) {
+      if (auto auxValue = dyn_cast<ValueDecl>(aux)) {
+        if (auxValue->getDeclContext() == expectedDC &&
+            knownAlternateMembers.insert(auxValue).second)
+          members.push_back(auxValue);
+      }
+    });
+
     // If this declaration shouldn't be visible, don't add it to
     // the list.
     if (shouldSuppressDeclImport(nd))

test/Inputs/clang-importer-sdk/usr/include/completion_handler_globals.h

@@ -1,2 +1,9 @@
 void async_divide(double x, double y, void (* _Nonnull completionHandler)(double x))
   __attribute__((swift_attr("@macro_library.AddAsync")));
+
+typedef struct SlowComputer {
+} SlowComputer;
+
+void computer_divide(const SlowComputer *computer, double x, double y, void (* _Nonnull completionHandler)(double x))
+  __attribute__((swift_attr("@macro_library.AddAsync")))
+  __attribute__((swift_name("SlowComputer.divide(self:_:_:completionHandler:)")));

test/Macros/expand_on_imported.swift

@@ -20,8 +20,9 @@ func asyncTest(_ value: Int, completionHandler: @escaping (String) -> Void) {
 }
 
 @available(SwiftStdlib 5.1, *)
-func testAll(x: Double, y: Double) async {
+func testAll(x: Double, y: Double, computer: SlowComputer) async {
   _ = await asyncTest(17)
 
   let _: Double = await async_divide(1.0, 2.0)
+  let _: Double = await computer.divide(x, y)
 }

test/Macros/print_clang_expand_on_imported.swift

@@ -12,5 +12,9 @@
 import CompletionHandlerGlobals
 
 // CHECK: func async_divide(_ x: Double, _ y: Double, _ completionHandler: @convention(c) (Double) -> Void)
+
+// CHECK: extension SlowComputer
+// CHECK: public func divide(_ x: Double, _ y: Double) async -> Double
+
 // CHECK: func async_divide(_ x: Double, _ y: Double) async -> Double