Add inherited member lookup test case

Author: j-hui

test/Interop/Cxx/class/inheritance/Inputs/inherited-lookup.h

@@ -0,0 +1,9 @@
+#pragma once
+
+struct Base1 {
+  int method(void) const { return 1; }
+};
+
+struct IBase1 : Base1 { };
+
+struct IIBase1 : IBase1 { };

test/Interop/Cxx/class/inheritance/Inputs/module.modulemap

@@ -43,3 +43,8 @@ module FunctionsObjC {
   requires cplusplus
   requires objc
 }
+
+module InheritedLookup {
+  header "inherited-lookup.h"
+  requires cplusplus
+}

test/Interop/Cxx/class/inheritance/inherited-lookup-executable.swift

@@ -0,0 +1,14 @@
+// RUN: %target-run-simple-swift(-I %S/Inputs/ -Xfrontend -cxx-interoperability-mode=default)
+//
+// REQUIRES: executable_test
+import InheritedLookup
+import StdlibUnittest
+
+var InheritedMemberTestSuite = TestSuite("Test if inherited lookup works")
+
+InheritedMemberTestSuite.test("IIBase1::method() resolves to grandparent") {
+  let iibase1 = IIBase1()
+  expectEqual(iibase1.method(), 1)
+}
+
+runAllTests()

test/Interop/Cxx/class/inheritance/inherited-lookup-typechecker.swift

@@ -0,0 +1,20 @@
+// RUN: %target-typecheck-verify-swift -verify-ignore-unknown -I %S/Inputs -cxx-interoperability-mode=default
+import InheritedLookup
+
+extension IIBase1 {
+    func ext() {
+        // NOTE: we deliberately look up a missing member above because doing so
+        // forces multiple ClangRecordMemberLookup requests, which should be
+        // idempotent (though this hasn't always been the case, because bugs).
+        missing() // expected-error {{cannot find 'missing' in scope}}
+
+        // For instance, a non-idempotent ClangRecordMemberLookup would cause
+        // the following to appear ambiguous:
+        method()
+    }
+}
+
+func f(v: IIBase1) {
+    v.missing() // expected-error {{'IIBase1' has no member 'missing'}}
+    v.method()
+}