[Clang importer] Report auxiliary decls from C++ member lookup

When performing name lookup into a C++ record type, make sure that we
also walk through auxiliary declarations (i.e., declarations that can
come from peer macro expansions) to find results.

Fixes rdar://146833294.

lib/ClangImporter/ClangImporter.cpp

@@ -6200,8 +6200,32 @@ TinyPtrVector<ValueDecl *> ClangRecordMemberLookup::evaluate(
       ClangDirectLookupRequest({recordDecl, recordDecl->getClangDecl(), name}),
       {});
 
-  // Find the results that are actually a member of "recordDecl".
+  // The set of declarations we found.
   TinyPtrVector<ValueDecl *> result;
+  auto addResult = [&result, name](ValueDecl *imported) {
+    result.push_back(imported);
+
+    // Expand any macros introduced by the Clang importer.
+    imported->visitAuxiliaryDecls([&](Decl *decl) {
+      auto valueDecl = dyn_cast<ValueDecl>(decl);
+      if (!valueDecl)
+        return;
+
+      // Bail out if the auxiliary decl was not produced by a macro.
+      auto module = decl->getDeclContext()->getParentModule();
+      auto *sf = module->getSourceFileContainingLocation(decl->getLoc());
+      if (!sf || sf->Kind != SourceFileKind::MacroExpansion)
+        return;
+
+      // Only produce results that match the requested name.
+      if (!valueDecl->getName().matchesRef(name))
+        return;
+
+      result.push_back(valueDecl);
+    });
+  };
+
+  // Find the results that are actually a member of "recordDecl".
   ClangModuleLoader *clangModuleLoader = ctx.getClangModuleLoader();
   for (auto foundEntry : directResults) {
     auto found = foundEntry.get<clang::NamedDecl *>();
@@ -6236,7 +6260,8 @@ TinyPtrVector<ValueDecl *> ClangRecordMemberLookup::evaluate(
       if (!imported)
         continue;
     }
-    result.push_back(cast<ValueDecl>(imported));
+
+    addResult(cast<ValueDecl>(imported));
   }
 
   if (inheritance) {
@@ -6255,7 +6280,7 @@ TinyPtrVector<ValueDecl *> ClangRecordMemberLookup::evaluate(
       if (!imported)
         continue;
 
-      result.push_back(cast<ValueDecl>(imported));
+      addResult(imported);
     }
   }
 
@@ -6304,7 +6329,7 @@ TinyPtrVector<ValueDecl *> ClangRecordMemberLookup::evaluate(
           if (foundNameArities.count(getArity(foundInBase)))
             continue;
 
-          result.push_back(foundInBase);
+          addResult(foundInBase);
         }
       }
     }

test/Interop/Cxx/swiftify-import/counted-by-method.swift

@@ -0,0 +1,30 @@
+// REQUIRES: swift_feature_SafeInteropWrappers
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUNx: %target-swift-ide-test -plugin-path %swift-plugin-dir -I %t/Inputs -cxx-interoperability-mode=upcoming-swift -enable-experimental-feature SafeInteropWrappers -print-module -module-to-print=Method -source-filename=x | %FileCheck %s
+// RUN: %target-swift-frontend -plugin-path %swift-plugin-dir -I %t/Inputs -cxx-interoperability-mode=default -enable-experimental-feature SafeInteropWrappers %t/method.swift -dump-macro-expansions -typecheck -verify
+
+// CHECK: @_alwaysEmitIntoClient 
+// CHECK:  public mutating func bar(_ p: UnsafeMutableBufferPointer<Int32>)
+
+//--- Inputs/module.modulemap
+module Method {
+    header "method.h"
+    requires cplusplus
+}
+
+//--- Inputs/method.h
+
+class Foo {
+public:
+   __attribute__((swift_attr("@_SwiftifyImport(.countedBy(pointer: .param(1), count: \"len\"))"))) void bar(float *p, int len);
+};
+
+//--- method.swift
+import Method
+  
+func test(s: UnsafeMutableBufferPointer<Float>) {
+  var foo = Foo()
+  foo.bar(s)
+}