Stdlib: json_encode and json_decode for API endpoints

[PurHur]

Problem

No JSON builtins in ext/standard/. Small web apps serving APIs need JSON responses. Blocks #270 (004-ApiJson example) and #67 /api/status route.

Goal

json_encode / json_decode for arrays and strings (VM + JIT + AOT when other stdlib builtins do).

Implementation hints

v1 scope (arrays only)

• VM: ext/standard/json_encode.php — delegate to PHP's json_encode/json_decode via existing builtin wrapper pattern (see htmlspecialchars, header).
• JIT: start with FFI/callout to libc is unnecessary; use Jit* helper calling PHP runtime or embed minimal encoder for array<string|int|bool|null> + string values only.
• AOT: same module registration as JIT once VM path exists.
• Register in ext/standard/Module.php; run script/capability-matrix.php and commit docs/capabilities.md diff.

Suggested files

Area	Path
VM builtin	ext/standard/json_encode.php, json_decode.php
JIT	ext/standard/JitJsonEncode.php (new, mirror JitHeader.php)
Tests	test/real/cases/json_encode_api.phpt, compliance mirror
Lint registry	lib/Lint/UnsupportedRegistry.php — remove if mapped

PHPT sketch

--FILE--
<?php
header('Content-Type: application/json');
echo json_encode(['ok' => true, 'n' => 1]);
--EXPECT--
{"ok":true,"n":1}

Tasks

• VM: encode assoc array, decode to array (objects → array for v1)
• JIT: at least json_encode for literal/array builds used by Examples: 004-ApiJson — minimal JSON API endpoint (lint-first) #270
• PHPT in test/real/cases/
• Capability matrix row

Scope v1

• Flags: defer JSON_THROW_ON_ERROR / JSON_INVALID_UTF8_*
• No JsonSerializable objects initially
• json_decode second; ship json_encode first for Examples: 004-ApiJson — minimal JSON API endpoint (lint-first) #270

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  ./phpc run -r "header('Content-Type: application/json'); echo json_encode(['ok'=>true]);"

Output matches PHP 8. VM + JIT; AOT when bin/compile.php supports the builtin.

Dependencies

• Stdlib: http_response_code() for 404/500 and API status #252 http_response_code() optional for status JSON APIs
• Language: JIT support for non-void function return types #55 non-void returns if handlers return encoded strings from functions

Verification (local only)

./script/ci-local.sh --filter json

Related

• Examples: 004-ApiJson — minimal JSON API endpoint (lint-first) #270 Example 004-ApiJson
• Stdlib: json_encode and json_decode for API endpoints #61 parent: 🗺️ ROADMAP: Compile a small PHP web application (living document) #78 Phase 4 stdlib

[PurHur]

Merged in #389: json_encode VM + JIT/AOT for assoc scalar arrays.