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Fix discarded nodiscard results across the test suite for GCC's warn_unused_result

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A plain (void) cast on a call expression suppresses the C++17 [[nodiscard]]
warning but not GCC's warning for functions annotated via the GNU
__attribute__((warn_unused_result)) form -- which is what
JSON_HEDLEY_WARN_UNUSED_RESULT expands to on GCC. Several existing tests
that call a newly-annotated function (dump(), empty()) purely to check
that it throws/does not throw, discarding the result via (void), newly
warned (and failed -Werror builds) once the annotation was broadened.
Route those discards through a small ignore_return_value() helper
instead, which actually consumes the value and suppresses the warning
on both attribute forms.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-06 12:18:38 +02:00
parent 354d5fa723
commit 7cb4d3284e
11 changed files with 63 additions and 22 deletions
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tests/src/unit-serialization.cpp
+11 -6
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@@ -15,6 +15,8 @@ using nlohmann::json;
#include <sstream>
#include <iomanip>
#include "test_utils.hpp"
TEST_CASE("serialization")
{
SECTION("operator<<")
@@ -84,8 +86,9 @@ TEST_CASE("serialization")
{
const json j = "ä\xA9ü";
CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
CHECK_THROWS_WITH_AS(j.dump(1, ' ', false, json::error_handler_t::strict), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
// dump() is nodiscard; the exception is thrown by dump() itself before it would return
CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump(1, ' ', false, json::error_handler_t::strict)), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"äü\"");
CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"ä\xEF\xBF\xBDü\"");
CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"\\u00e4\\ufffd\\u00fc\"");
@@ -95,8 +98,9 @@ TEST_CASE("serialization")
{
const json j = "123\xC2";
CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0xC2", json::type_error&);
CHECK_THROWS_AS(j.dump(1, ' ', false, json::error_handler_t::strict), json::type_error&);
// dump() is nodiscard; the exception is thrown by dump() itself before it would return
CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0xC2", json::type_error&);
CHECK_THROWS_AS(utils::ignore_return_value(j.dump(1, ' ', false, json::error_handler_t::strict)), json::type_error&);
CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"123\"");
CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"123\xEF\xBF\xBD\"");
CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"123\\ufffd\"");
@@ -106,8 +110,9 @@ TEST_CASE("serialization")
{
const json j = "123\xF1\xB0\x34\x35\x36";
CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 5: 0x34", json::type_error&);
CHECK_THROWS_AS(j.dump(1, ' ', false, json::error_handler_t::strict), json::type_error&);
// dump() is nodiscard; the exception is thrown by dump() itself before it would return
CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] invalid UTF-8 byte at index 5: 0x34", json::type_error&);
CHECK_THROWS_AS(utils::ignore_return_value(j.dump(1, ' ', false, json::error_handler_t::strict)), json::type_error&);
CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"123456\"");
CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"123\xEF\xBF\xBD\x34\x35\x36\"");
CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"123\\ufffd456\"");