Return an empty string instead of asserting in clang-repl toString

lib/CppInterOp/CppInterOp.td

@@ -275,7 +275,9 @@ calling dlopen.
 }
 
 def ObjToString : CppInterOpAPI {
-  let Doc = "Tries to load provided objects in a string format (prettyprint).";
+  let Doc = [{Tries to load provided objects in a string format (prettyprint).
+Returns an empty string if the object has no string representation. This is
+always the case with clang-repl, which does not implement it yet.}];
 
   let ReturnType = "std::string";
   let Args = [

lib/CppInterOp/CppInterOpInterpreter.h

@@ -749,11 +749,10 @@ class Interpreter {
     }
   }
 
-  std::string toString(const char* type, void* obj) {
-    assert(0 && "toString is not implemented!");
-    std::string ret;
-    return ret; // TODO: Implement
-  }
+  // FIXME: Implement on top of clang-repl's value printer once it supports
+  // user-defined types. Until then report "no representation" with an empty
+  // string, the same way in every build, so callers can fall back.
+  std::string toString(const char* /*type*/, void* /*obj*/) { return {}; }
 
   CompilationResult undo(unsigned N = 1) {
     if (llvm::Error Err = Undo(N)) {

unittests/CppInterOp/InterpreterTest.cpp

@@ -753,6 +753,18 @@ TYPED_TEST(CPPINTEROP_TEST_MODE, Interpreter_DeclareReportsParseErrors) {
                             /*silent=*/false));
 }
 
+TYPED_TEST(CPPINTEROP_TEST_MODE, Interpreter_ObjToString) {
+  TestFixture::CreateInterpreter();
+
+  int Value = 42;
+#ifdef CPPINTEROP_USE_CLING
+  EXPECT_FALSE(Cpp::ObjToString("int", &Value).empty());
+#else
+  // Not implemented for clang-repl: an empty string, not an abort.
+  EXPECT_EQ(Cpp::ObjToString("int", &Value), "");
+#endif
+}
+
 TYPED_TEST(CPPINTEROP_TEST_MODE, Interpreter_EmscriptenExceptionHandling) {
 #ifndef EMSCRIPTEN
   GTEST_SKIP() << "This test is intended to check exception handling for Emscripten builds.";