Stdlib: mb_convert_encoding / mb_detect_encoding (ext/mbstring parity)

[PurHur]

Category

stdlib

Problem

Only mb_strlen() is implemented (ext/types/mb_strlen.php). Web and CLI apps need mb_convert_encoding() and mb_detect_encoding() for charset pipelines (form uploads, legacy ISO-8859-1 sources, UTF-8 normalization).

Both functions are undefined in this compiler today.

php-src reference

• php/php-src ext/mbstring/mbstring.c — php_mb_convert_encoding, php_mb_detect_encoding
• php/php-src ext/mbstring/mbstring.stub.php — signatures and MB_* constants
• php/php-src ext/mbstring/libmbfl — conversion engine (v1 may delegate to host mb_* on Zend harness)

Repro (today)

<?php
$iso = "\xE9"; // é in ISO-8859-1
echo mb_convert_encoding($iso, 'UTF-8', 'ISO-8859-1'), "\n";
echo mb_detect_encoding($iso, ['ISO-8859-1', 'UTF-8'], true), "\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php repro.php'
# Call to undefined function mb_convert_encoding()

./script/docker-exec.sh -- bash -lc 'php repro.php'
# UTF-8 é + ISO-8859-1

Scope (this repo)

Piece	Path
Module	new ext/mbstring/Module.php or extend ext/types/
VM	delegate to host \mb_convert_encoding / \mb_detect_encoding when ext/mbstring loaded; clear error when unavailable
Register	ext/standard/Module.php or dedicated mbstring module loader
v1 surface	mb_convert_encoding, mb_detect_encoding (+ MB_* encoding name constants subset)
JIT	Deferred (VM-first)
Tests	test/compliance/cases/stdlib/mb_convert_encoding.phpt, mb_detect_encoding.phpt

Done when

• Repro output byte-identical to Zend on Docker harness (UTF-8 é + ISO-8859-1)
• Invalid encoding name → false + warning (Zend parity)
• Capability matrix rows added via script/capability-matrix.php
• ./script/ci-fast.sh --filter MbConvert green

Related

• Stdlib: mb_str_pad() — multibyte string padding (ext/mbstring/mbstring.c parity) #4006 / Stdlib: mb_lcfirst() / mb_ucfirst() — multibyte case change (ext/mbstring/mbstring.c parity) #4007 (other mbstring) · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

Spec refresh — implementation-ready (2026-06-20)

Verified on harness host:

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php -r "var_export(function_exists(\"mb_convert_encoding\")); echo PHP_EOL; var_export(function_exists(\"mb_detect_encoding\"));"'
# bool(false) bool(false)

Function	Zend	VM
function_exists('mb_convert_encoding')	true	false
function_exists('mb_detect_encoding')	true	false
mb_convert_encoding("\xE9", 'UTF-8', 'ISO-8859-1')	UTF-8 é	undefined function

Scope (this repo)

Layer	Path
VM	ext/mbstring/VmMbstring.php — add convertEncoding(), detectEncoding()
Builtins	ext/mbstring/mb_convert_encoding.php, mb_detect_encoding.php
Register	ext/mbstring/Module.php
JIT	ext/mbstring/JitMbConvertEncoding.php — defer v1 OK if VM-only noted in matrix
Tests	test/compliance/cases/stdlib/mb_convert_encoding_iso.phpt, mb_detect_encoding.phpt

PHP-in-PHP: v1 may wrap host mb_* on Zend harness for parity proofs; ship pure-PHP tables in ext/mbstring/ for self-host/AOT (no permanent C conversion tables).

Done when

• Repro A/B from issue body pass on VM (php-src-strict)
• Invalid encoding names Warning/false match Zend
• Enum case $str operands TypeError like Zend string builtins
• ./script/ci-fast.sh --filter mb_convert_encoding green
• Close Stdlib: iconv() / mb_convert_encoding() — charset conversion (ext/iconv + ext/mbstring parity) #3222 umbrella slice or note overlap in PR

Worker anchor: implement with #3222 in one PR when practical.

[PurHur]

claim: PHP Compiler Ext — I/O & Crypto — starting this run (mb_detect_encoding — completes #3075 slice)

[PurHur]

Merged via #17848

Fix: mb_detect_encoding() registered in ext/mbstring/ with Zend-aligned detection (UTF-8 preference for valid multibyte UTF-8 vs ISO-8859-1). Completes #3075 alongside existing mb_convert_encoding().

Verification:

source script/php-env.sh
php bin/vm.php test/repro/maintainer_gap_mb_detect_encoding.php
./script/phpunit.sh --filter mb_detect_encoding
php script/check-selfhost-spine-coverage-sync.php

Repro prints ok; PHPUnit OK (2 tests); spine sync OK (4403/4404).