Language: $false[] = $v fatals — Zend promotes false to array like null (Zend/zend_execute.c)

[PurHur]

Category

Language: · php-src-strict · auto-array promotion on append

Problem

Appending with [] = to null correctly promotes to an array. Appending to false must do the same (legacy Zend auto-conversion). The VM throws Error: Cannot use a scalar value as an array instead.

true correctly fatals on both engines; only false (and historically null) promote.

Repro	Zend 8.2+ (2026-07-23)	VM (2026-07-23)
$f=false; $f[]=1;	array(0=>1) type array	fatal scalar-as-array
$n=null; $n[]=1;	array(0=>1)	array(0=>1) ✅
$t=true; $t[]=1;	fatal scalar-as-array	fatal scalar-as-array ✅

php-src reference

• php/php-src Zend/zend_execute.c — zend_assign_to_variable / dim write; false/null → empty array before append
• php/php-src Zend/zend_operators.c — scalar→array conversion rules for []

PHP implementation target

• lib/VM.php (and shared dim-write / append lowering) — treat false like null when the write is [] = append
• Mirror in lib/JIT/ dim-write if AOT/JIT diverge
• Prefer PHP lowering; no new C runtime logic

Repro

./script/docker-exec.sh -- bash -lc 'php test/repro/maintainer_gap_false_append_promotes_array.php; php bin/vm.php test/repro/maintainer_gap_false_append_promotes_array.php'
# Zend: array ( 0 => 1, ) / array
# VM: Fatal Error Cannot use a scalar value as an array

Done when

• $f=false; $f[]=1; yields [1] matching Zend on VM (and JIT/AOT when in scope)
• true / int / float still Error
• Compliance .phpt under test/compliance/cases/language/
• php-src-strict; no php-compiler-strict shortcut

[PurHur]

claim: worker-lane-A — starting this run

Gate snapshot (before implement):

• docker info: ok
• php script/bootstrap-inventory.php --check: partial/red — file-list drift (JIT StringOffset / Variable / GcToggleRuntime construct counts); regenerate path noted
• release-readiness --json: still running (prior maintainer notes: user_release_ready: no, north-star5-fast 4f-m gen-0 fingerprint Self-host M5: bootstrap-inventory argv driver size floor — grow beyond 451KB stub #8713)
• Proceeding with language parity Language: $false[] = $v fatals — Zend promotes false to array like null (Zend/zend_execute.c) #22650 (false []= promote like null) — not a bootstrap/gen-0 touch

[PurHur]

Merged #22667

Verification

• php bin/vm.php test/repro/maintainer_gap_false_append_promotes_array.php → array ( 0 => 1, ) / array
• ./script/phpunit.sh --filter 'append_false_promotes_array|append_scalar_bool_error|coalesce_assign_dim_null_autovivify' → OK (6 tests)

Fix: false treated like null/undefined for FETCH_DIM_W autovivify in TypeCheck; true/int/float still scalar-as-array Error. JIT NATIVE_BOOL write path matches.