Stdlib: json_encode() — enum case operands must match Zend JSON output (ext/json/php_json.c)

[PurHur]

Summary

json_encode() on enum case operands must match Zend/php-src JSON serialization rules. Today the VM path fails in VmJson::export() with a generic LogicException before JSON is produced.

Strictness: php-src-strict — match ext/json/php_json.c enum handling.

php-src reference

• ext/json/php_json.c — php_json_encode() / enum case handling
• Zend/zend_enum.c — backed vs unit enum JSON representation

Repro

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php test/repro-maintainer/parity_json_encode_enum.php'

Compare with Zend in the same container:

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php test/repro-maintainer/parity_json_encode_enum.php'

Zend PHP 8.2 (expected):

unit: 
backed_string: "x"
backed_int: 1

php-compiler VM (actual):

unit: json_encode() value type not supported in this compiler build

Expected behavior

Operand	Zend JSON
unit enum case	"" (empty JSON string)
backed string case	quoted backing value, e.g. "x"
backed int case	numeric backing value, e.g. 1

Implementation hints (PHP-in-PHP)

• Extend ext/standard/VmJson.php::export() for Variable::TYPE_ENUM_CASE.
• Wire the same rules in ext/standard/json_encode.php JIT lowering.
• Add compliance .phpt under test/compliance/cases/stdlib/ + JIT/AOT fixtures.
• Do not add C runtime logic in runtime/.

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter json_encode_enum test/compliance/'

Maintainer repro: test/repro-maintainer/parity_json_encode_enum.php

Category

php-in-php | stdlib

Done when

• Repro test/repro-maintainer/parity_json_encode_enum.php prints unit "", backed string "x", backed int 1 on VM — matching Zend side-by-side in Docker
• VmJson::export() handles TYPE_ENUM_CASE; no LogicException abort on enum operands
• json_encode() JIT lowering mirrors VM rules (or documents VM-only v1 in capability matrix)
• Compliance json_encode_enum filter green; enum-case TypeError cases where php-src rejects operands
• Pairs bootstrap issue php-in-php: VmJson::export() — enum case JSON must not abort with LogicException (ext/json/php_json.c, bootstrap) #6598 for self-host JSON paths without Zend

[PurHur]

Implementation-ready expansion (parity backlog architect, 2026-06-05)

Done when

• test/repro-maintainer/parity_json_encode_enum.php passes on php bin/vm.php with Zend-matching output for unit + backed cases
• json_encode() JIT/AOT lowering applies the same VmJson::export() enum rules (no host \json_encode() on enum operands)
• test/compliance/cases/stdlib/json_encode_enum.phpt green under VM + JIT filter
• test/fixtures/aot/cases/json_encode_enum.phpt green when AOT user-script gate applies
• No new logic in lib/AOT/runtime/phpc_json_decode.c / JSON C helpers — behavior stays in ext/standard/VmJson*.php per #6202

Verification commands

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php test/repro-maintainer/parity_json_encode_enum.php'
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./script/ci-fast.sh --filter json_encode_enum'

php-src-strict note

Unit enum cases encode as JSON "" (empty string), not case name. Backed cases encode backing scalar only — never "name" object shapes.

[PurHur]

claim: PHP Runtime → PHP — starting this run (#6130: fix json_encode enum repro/compliance — VmJson already handles TYPE_ENUM_CASE).

[PurHur]

Merged via #7801.

Root cause: repro/compliance used enum UnitEnum which conflicts with PHP's built-in UnitEnum interface — scripts exited 255 before json_encode() ran. VmJson::exportEnumCase() and JIT StringJsonEncode enum branch were already correct on master.

Fix: rename unit enum to UE; add json_encode_enum_case_jit.phpt.

Verification (green):

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter json_encode_enum'
# OK (2 tests, 2 assertions)