Stdlib: PHP 8.4 forward-profile gated builtins — function_exists/extension_loaded true on reference profile (ext/standard)

[PurHur]

Category

stdlib · php-src-strict · forward-profile registration

Problem

With PHP_COMPILER_PROFILE=8.4, builtins and extensions that Zend 8.2 does not expose report as present via function_exists() / extension_loaded(). This breaks parity scripts that gate on reference-profile availability before calling forward-only APIs.

Probe	Zend 8.2 (reference)	VM profile=8.4 (2026-07-04)
function_exists('fpow')	false	true
function_exists('mb_str_pad')	false	true
extension_loaded('bcmath')	false	true

php-src reference

• php/php-src ext/standard/basic_functions.c — php_register_standard_extensions, function_exists registry
• php/php-src ext/bcmath/bcmath.c — optional extension registration

PHP implementation target

• ext/standard / builtin registration tables — withhold forward-profile symbols from function_exists until the active runtime profile matches php-src for that symbol
• lib/ extension probe helpers — align extension_loaded() with Zend reference profile semantics

Repro

./script/docker-exec.sh -- bash -lc '
  export PHP_COMPILER_PROFILE=8.4
  php bin/vm.php test/repro/maintainer_gap_fpow_phantom_registration.php      # exit=1
  php bin/vm.php test/repro/maintainer_gap_mb_str_pad_phantom_function_exists.php  # exit=1
  php bin/vm.php test/repro/maintainer_gap_bcmath_phantom_registration.php    # exit=1
'

Done when

• All three probes print ok (exit 0) on VM with PHP_COMPILER_PROFILE=8.4 against Zend 8.2 reference
• Forward builtins still callable when profile + php-src version both allow them
• Compliance guard for function_exists / extension_loaded gating
• php-src-strict; no php-compiler-strict shortcut

[PurHur]

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

[PurHur]

Merged via #16093.

Fix: Split callable registration (supports*, languageProfileVersion) from introspection advertisement (advertises*, stable VERSION). BuiltinIntrospectionPolicy filters function_exists() / extension_loaded('bcmath') so forward profile keeps fpow/mb_str_pad/bc* callable while matching Zend 8.2 phantom probes.

Verification (PHP_COMPILER_PROFILE=8.4):

• maintainer_gap_fpow_phantom_registration.php → ok
• maintainer_gap_mb_str_pad_phantom_function_exists.php → ok
• maintainer_gap_bcmath_phantom_registration.php → ok
• forward_profile_phantom_introspection.phpt → ok, callable=1