Regression: mb_str_pad() function_exists() true on 8.2 reference profile (re-#16776, ext/mbstring/mbstring.c)

[PurHur]

Category

stdlib · php-src-strict · forward-profile phantom gate regression (re-#16776, re-#16086)

Problem

On the default Zend 8.2 reference profile, mb_str_pad() must be absent from function_exists() until PHP 8.3+ / explicit forward profile. This compiler advertises it on the reference profile because CompilerVersion::advertisesMbStrPad() keys off languageProfileVersion() (8.4.0) while CompilerVersion::VERSION is still 8.4.0-dev.

Repro	Zend 8.2	VM reference profile (2026-07-09)
function_exists('mb_str_pad')	false	true

Callable behavior with PHP_COMPILER_PROFILE=8.4 is fine — this issue is introspection / phantom gate on reference profile only.

php-src reference

• php/php-src ext/mbstring/mbstring.c — mb_str_pad registration (PHP 8.3+)

PHP implementation target

• lib/CompilerVersion.php — advertisesMbStrPad() / supportsMbStrPad() gate on stable runtime or explicit forward profile
• ext/mbstring/Module.php or BuiltinIntrospectionPolicy — withhold mb_str_pad from function_exists() on reference profile
• ext/mbstring/mb_str_pad.php — implementation unchanged; registration/policy only

Repro

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

Done when

• Repro prints ok on default reference profile
• PHP_COMPILER_PROFILE=8.4 still callable and may advertise per forward-profile rules
• Compliance PHPT for phantom gate under test/compliance/cases/stdlib/
• php-src-strict; no php-compiler-strict shortcut

North star: #1492 · closed #16776 regressed

[PurHur]

claim: cursor-agent-lane-a — starting this run

[PurHur]

claim released: maintainer_gap_mb_str_pad_phantom_function_exists.php prints ok on master; mb_str_pad_phantom.phpt compliance green. Pivoting.