Regression: json_encode(unit enum) json_last_error_msg wrong — Zend Non-backed enums… (ext/json/php_json.c)

[PurHur]

Category

stdlib · php-src-strict · JSON enum encoding (pillar 4)

Problem

json_encode on a unit (non-backed) enum case returns false on both engines, but json_last_error_msg() diverges:

• Zend: Non-backed enums have no default serialization
• VM: Type is not supported

Backed enums already encode to their scalar (OK). Respin surface of closed #6130 / #5683 — encoding result is false, but the error string must match php-src for debuggers and JSON_THROW_ON_ERROR message text.

Probed 2026-07-23 on master VM vs host Zend 8.2.32.

Repro	Zend 8.2+	VM (2026-07-23)
json_encode(U::X) (unit enum)	false	false
json_last_error_msg() after	Non-backed enums have no default serialization	Type is not supported

php-src reference

• php/php-src ext/json/json_encoder.c — unit enum reject path / error message
• php/php-src Zend/zend_enum.c — backed vs unit distinction

PHP implementation target

• ext/json/ or JSON encode helper — special-case unit enum before generic unsupported-type path; set last-error string to Zend wording
• JSON_THROW_ON_ERROR must surface the same message
• PHP-in-PHP only

Repro

./script/docker-exec.sh -- bash -lc 'php bin/vm.php -r '\"'\"'
enum U { case X; }
var_export(json_encode(U::X)); echo \"\n\";
echo json_last_error_msg(), \"\n\";
'\"'\"''

Expected (Zend): false then Non-backed enums have no default serialization
Actual (VM): false then Type is not supported

Done when

• Unit-enum json_encode last-error / throw message matches Zend on VM/JIT/AOT
• Compliance .phpt under test/compliance/cases/json/
• php-src-strict; no php-compiler-strict shortcut

[PurHur]

claim: PHP Compiler STD Lib — starting this run

Focus: json_encode(unit enum) last-error message vs Zend (Non-backed enums have no default serialization). Will also check #22688 (PROFILE=8.4 ValueError) on the same encode path.

[PurHur]

Merged via #22726

Fix: VmJson::exportEnumCase → JSON_ERROR_NON_BACKED_ENUM (11) + Zend message; retired forward-profile ValueError gate (#22688).

Verified:

• Zend / bin/vm.php / bin/jit.php repro identical (false / 11:Non-backed… / JsonException)
• PHP_COMPILER_PROFILE=8.4 no longer ValueError
• compliance json_encode_unit_enum_non_backed*.phpt OK

AOT enum encode still segfaults at runtime (pre-existing); JIT shares the fixed helper.