Test C++ out-of-line operator functions (swiftlang#32081)

Add tests to verify that C++ out-of-line operator functions are
imported correctly.

Author: MForster

test/Interop/Cxx/operators/Inputs/module.modulemap

@@ -1,3 +1,7 @@
 module NonMemberInline {
   header "non-member-inline.h"
 }
+
+module NonMemberOutOfLine {
+  header "non-member-out-of-line.h"
+}

test/Interop/Cxx/operators/Inputs/non-member-out-of-line.cpp

@@ -0,0 +1,5 @@
+#include "non-member-out-of-line.h"
+
+IntBox operator+(IntBox lhs, IntBox rhs) {
+  return IntBox{.value = lhs.value + rhs.value};
+}

test/Interop/Cxx/operators/Inputs/non-member-out-of-line.h

@@ -0,0 +1,10 @@
+#ifndef TEST_INTEROP_CXX_OPERATORS_INPUTS_NON_MEMBER_OUT_OF_LINE_H
+#define TEST_INTEROP_CXX_OPERATORS_INPUTS_NON_MEMBER_OUT_OF_LINE_H
+
+struct IntBox {
+  int value;
+};
+
+IntBox operator+(IntBox lhs, IntBox rhs);
+
+#endif

test/Interop/Cxx/operators/non-member-out-of-line-irgen.swift

@@ -0,0 +1,8 @@
+// RUN: %target-swift-emit-ir %s -I %S/Inputs -enable-cxx-interop | %FileCheck %s
+
+import NonMemberOutOfLine
+
+public func add(_ lhs: IntBox, _ rhs: IntBox) -> IntBox { lhs + rhs }
+
+// CHECK: call i32 [[NAME:@(_Zpl6IntBoxS_|"\?\?H@YA\?AUIntBox@@U0@0@Z")]](i32 %{{[0-9]+}}, i32 %{{[0-9]+}})
+// CHECK: declare {{(dso_local )?}}i32 [[NAME]](i32, i32)

test/Interop/Cxx/operators/non-member-out-of-line-silgen.swift

@@ -0,0 +1,10 @@
+// RUN: %target-swift-emit-sil %s -I %S/Inputs -enable-cxx-interop | %FileCheck %s
+
+import NonMemberOutOfLine
+
+public func add(_ lhs: IntBox, _ rhs: IntBox) -> IntBox { lhs + rhs }
+
+// CHECK: [[COUNTER:%.*]] = function_ref [[NAME:@(_Zpl6IntBoxS_|\?\?H@YA\?AUIntBox@@U0@0@Z)]] : $@convention(c) (IntBox, IntBox) -> IntBox
+// CHECK: apply [[COUNTER]](%0, %1) : $@convention(c) (IntBox, IntBox) -> IntBox
+
+// CHECK: sil [serializable] [clang "+"] [[NAME]] : $@convention(c) (IntBox, IntBox) -> IntBox

test/Interop/Cxx/operators/non-member-out-of-line.swift

@@ -0,0 +1,23 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-clang -c %S/Inputs/non-member-out-of-line.cpp -I %S/Inputs -o %t/non-member-out-of-line.o -std=c++17
+// RUN: %target-build-swift %s -I %S/Inputs -o %t/non-member-out-of-line %t/non-member-out-of-line.o -Xfrontend -enable-cxx-interop
+// RUN: %target-codesign %t/non-member-out-of-line
+// RUN: %target-run %t/non-member-out-of-line
+//
+// REQUIRES: executable_test
+
+import NonMemberOutOfLine
+import StdlibUnittest
+
+var OperatorsTestSuite = TestSuite("Operators")
+
+OperatorsTestSuite.test("plus") {
+  let lhs = IntBox(value: 42)
+  let rhs = IntBox(value: 23)
+
+  let result = lhs + rhs
+
+  expectEqual(65, result.value)
+}
+
+runAllTests()