Bootstrap: ext/mbstring/ module skeleton — register mbstring builtins for self-host (M4)

[PurHur]

Category

bootstrap | stdlib

Problem

Open mbstring parity issues (#4405 mb_strlen, #3239 mb_substr, #3075 mb_convert_encoding, …) assume an ext/mbstring/ entry point like php-src, but this repo only has ext/standard + ext/types. mb_* helpers are absent from ext/standard/Module.php; there is no ext/mbstring/Module.php and no bootstrap inventory path for mbstring.

Self-host (#1492) needs a single module registration surface before individual mb builtins land.

php-src reference

• php/php-src ext/mbstring/mbstring.c — PHP_MINIT, function table
• php/php-src ext/mbstring/php_mbregex.c — optional regex subset

Repro (failure today)

ls -d ext/mbstring 2>&1 || echo "missing ext/mbstring"
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php -r "var_export(function_exists(\"mb_strlen\")); echo PHP_EOL;"'
# Zend: true — VM: false

Runtime	function_exists('mb_strlen')
Zend PHP 8.2 (Docker)	true
bin/vm.php	false

Scope (this repo)

Area	Path
New module	ext/mbstring/Module.php
Loader	Wire next to ext/standard/Module.php in runtime module init
v1	Register stub mb_strlen (or delegate to strlen with documented gap) so function_exists + inventory include the module
Inventory	script/bootstrap-inventory.php lists ext/mbstring/*
Follow-ups	Real algorithms in #4405, #3239, etc. — not this issue

Done when

• ext/mbstring/Module.php loads on VM without Zend PHP
• function_exists('mb_strlen') is true (implementation may be minimal stub documented in issue body)
• php script/bootstrap-inventory.php --check includes mbstring paths
• ./script/ci-fast.sh --filter mbstring green for skeleton registration test

Links

• Bootstrap: ext/spl/ module skeleton — register SPL builtin classes for self-host (M4) #4769 — SPL module skeleton (same pattern)
• Stdlib: mb_strlen() — encoding argument + error behavior parity with php-src ext/mbstring #4405 — first real builtin
• North star Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: worker-lane-b — starting this run

[PurHur]

Merged via #5863

Verification

• function_exists('mb_strlen') → true on VM
• MbstringModuleTest — OK (1 test)
• vendor/bin/phpunit --filter mb_strlen test/compliance/ — OK (6 tests)
• php script/bootstrap-inventory.php --check — OK 1399/1399 (includes ext/mbstring/*)

mb_strlen moved from ext/types/ to new ext/mbstring/Module.php registered in Runtime::loadCoreModules(). Follow-up real mbstring builtins remain in #4405, #3239, etc.

[PurHur]

Expanded spec — parity backlog architect (2026-06-18)

Status: implementation-ready (registration slice for self-host M4).

Maintainer repro (today)

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php -r "
echo function_exists(\"mb_strlen\")?\"yes\":\"no\", PHP_EOL;
echo function_exists(\"mb_convert_encoding\")?\"yes\":\"no\", PHP_EOL;
"'
# Expected today: no / no (or partial stubs)

<?php
// control: after skeleton lands, existence only (behavior → #3075 / #3222)
var_export(function_exists('mb_strlen'));
var_export(function_exists('mb_internal_encoding'));

Check	Zend	VM today
extension_loaded('mbstring') or function_exists('mb_strlen')	true	false
class_exists('mbstring') module registered	n/a	false

php-src reference (registration)

• ext/mbstring/mbstring.c — PHP_MINIT, mbstring_functions[]
• ext/mbstring/php_mbregex.c — defer regex to follow-up

Scope reminder

1. ext/mbstring/Module.php — register no-op or VM-delegate stubs for core symbols in script/bootstrap-inventory.php
2. ext/mbstring/VmMbstring.php — wire existing trim helpers; full convert → Stdlib: mb_convert_encoding / mb_detect_encoding (ext/mbstring parity) #3075 / Stdlib: iconv() / mb_convert_encoding() — charset conversion (ext/iconv + ext/mbstring parity) #3222
3. script/capability-matrix.php — rows marked VM-only until behavior lands
4. No new C in runtime/ — PHP module + JIT lowering only

Done when (this issue only — skeleton)

• function_exists('mb_strlen') true on VM after ext/mbstring/Module.php loads
• php script/bootstrap-inventory.php --check still green (inventory expects module path)
• test/compliance/cases/mbstring/module_registered.phpt — existence smoke
• ./script/ci-fast.sh --filter mbstring_module green

Verification

php script/bootstrap-inventory.php --check
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter mbstring_module'

Behavior parity (encoding conversion) is explicitly out of scope here → #3075, #3222, #3299.