Core: Improve vformat error reporting on sprintf failure

And fix a few occurrences of formatting errors that led me to this.

core/variant/array.cpp

@@ -235,7 +235,7 @@ void Array::assign(const Array &p_array) {
 		for (int i = 0; i < size; i++) {
 			const Variant &element = source[i];
 			if (element.get_type() != Variant::NIL && (element.get_type() != Variant::OBJECT || !typed.validate_object(element, "assign"))) {
-				ERR_FAIL_MSG(vformat(R"(Unable to convert array index %i from "%s" to "%s".)", i, Variant::get_type_name(element.get_type()), Variant::get_type_name(typed.type)));
+				ERR_FAIL_MSG(vformat(R"(Unable to convert array index %d from "%s" to "%s".)", i, Variant::get_type_name(element.get_type()), Variant::get_type_name(typed.type)));
 			}
 		}
 		_p->array = p_array._p->array;
@@ -258,11 +258,11 @@ void Array::assign(const Array &p_array) {
 				continue;
 			}
 			if (!Variant::can_convert_strict(value->get_type(), typed.type)) {
-				ERR_FAIL_MSG("Unable to convert array index " + itos(i) + " from '" + Variant::get_type_name(value->get_type()) + "' to '" + Variant::get_type_name(typed.type) + "'.");
+				ERR_FAIL_MSG(vformat(R"(Unable to convert array index %d from "%s" to "%s".)", i, Variant::get_type_name(value->get_type()), Variant::get_type_name(typed.type)));
 			}
 			Callable::CallError ce;
 			Variant::construct(typed.type, data[i], &value, 1, ce);
-			ERR_FAIL_COND_MSG(ce.error, vformat(R"(Unable to convert array index %i from "%s" to "%s".)", i, Variant::get_type_name(value->get_type()), Variant::get_type_name(typed.type)));
+			ERR_FAIL_COND_MSG(ce.error, vformat(R"(Unable to convert array index %d from "%s" to "%s".)", i, Variant::get_type_name(value->get_type()), Variant::get_type_name(typed.type)));
 		}
 	} else if (Variant::can_convert_strict(source_typed.type, typed.type)) {
 		// from primitives to different convertible primitives
@@ -270,7 +270,7 @@ void Array::assign(const Array &p_array) {
 			const Variant *value = source + i;
 			Callable::CallError ce;
 			Variant::construct(typed.type, data[i], &value, 1, ce);
-			ERR_FAIL_COND_MSG(ce.error, vformat(R"(Unable to convert array index %i from "%s" to "%s".)", i, Variant::get_type_name(value->get_type()), Variant::get_type_name(typed.type)));
+			ERR_FAIL_COND_MSG(ce.error, vformat(R"(Unable to convert array index %d from "%s" to "%s".)", i, Variant::get_type_name(value->get_type()), Variant::get_type_name(typed.type)));
 		}
 	} else {
 		ERR_FAIL_MSG(vformat(R"(Cannot assign contents of "Array[%s]" to "Array[%s]".)", Variant::get_type_name(source_typed.type), Variant::get_type_name(typed.type)));

core/variant/variant.h

@@ -857,7 +857,7 @@ String vformat(const String &p_text, const VarArgs... p_args) {
 	bool error = false;
 	String fmt = p_text.sprintf(args_array, &error);
 
-	ERR_FAIL_COND_V_MSG(error, String(), fmt);
+	ERR_FAIL_COND_V_MSG(error, String(), String("Formatting error in string \"") + p_text + "\": " + fmt + ".");
 
 	return fmt;
 }

modules/gdscript/tests/scripts/runtime/errors/typed_array_assign_wrong_to_typed.out

@@ -1,4 +1,5 @@
 GDTEST_RUNTIME_ERROR
 >> ERROR
 >> Method/function failed.
+>> Unable to convert array index 0 from "Object" to "Object".
 not ok