Regression: string offset assign of array omits Array to string conversion warning (Zend/zend_execute.c)

[PurHur]

Category

bug · php-src-strict · language · string offsets

Problem

Assigning an array to a string offset must emit E_WARNING: Array to string conversion before Only the first byte will be assigned to the string offset, then write the first byte of "Array" (A). The VM skips the Array-to-string warning and only emits the first-byte warning (result string still matches).

Distinct from #22895 (illegal dimension types → TypeError) and #22897 (assign-op on string offset).

Verified 2026-07-24 (Zend 8.2.32 vs php bin/vm.php, error_reporting(E_ALL)):

Repro	Zend 8.2	VM
$s="ab"; $s[0]=[];	Warning: Array to string conversion and Warning: Only the first byte… → 'Ab'	Only first-byte warning → 'Ab'

php-src reference

• php/php-src Zend/zend_execute.c — string offset assign / zend_assign_to_string_offset
• php/php-src Zend/zend_operators.c — array to string conversion

PHP implementation target

• lib/VM/ string-offset assign path — coerce array RHS via Zend-compatible cast (emit Array to string conversion) before first-byte assign
• JIT string-offset lowering must agree; no new runtime/*.c

Repro

./script/docker-exec.sh -- bash -lc 'php -r '"'"'error_reporting(E_ALL); $s="ab"; $s[0]=[]; var_export($s); echo "\n";'"'"''
./script/docker-exec.sh -- bash -lc 'php bin/vm.php -r '"'"'error_reporting(E_ALL); $s="ab"; $s[0]=[]; var_export($s); echo "\n";'"'"''

Done when

• Assigning [] (and other arrays) to a string offset emits Array to string conversion like Zend
• First-byte warning + resulting string unchanged vs Zend
• Compliance .phpt guard; php-src-strict; no php-compiler-strict shortcut