Language: @$undef as assignment RHS still warns — Zend silences (ZEND_BEGIN_SILENCE) #29132

Category

bug · php-src-strict · pillar 4 (correctness)

Problem

$a = @$undef; still emits E_WARNING: Undefined variable $undef on VM/JIT. Zend silences the warning (stderr empty). Bare @$undef; and @$arr['missing'] already match Zend on VM — the gap is specifically error-control applied to an undefined variable used as the RHS of assignment.

Verified 2026-08-08 vs Zend 8.2.32 (bin/vm.php + bin/jit.php).

php-src reference

• php/php-src Zend/zend_compile.c — ZEND_SILENCE / compile of @
• php/php-src Zend/zend_execute.c — ZEND_BEGIN_SILENCE / ZEND_END_SILENCE around CV fetch

PHP implementation target

• Ensure ErrorSuppressBlock / silence frame covers CV fetch when @ wraps the RHS of = (assign opcode + silenced fetch)
• lib/ lowering + VM silence; JIT must match (re-Language: @ error-control operator — JIT/AOT native silence (phase 2 of #3546) #4070 covered broader JIT silence — this is a remaining VM/JIT assign+CV hole)
• No new C runtime

Repro

./script/docker-exec.sh -- bash -lc 'cat > /tmp/at_rhs.php <<'"'"'PHP'"'"'
<?php
error_reporting(E_ALL);
$a = @$undef;
echo \"ok\n\";
PHP
php /tmp/at_rhs.php; echo ---; php bin/vm.php /tmp/at_rhs.php; echo ---; php bin/jit.php /tmp/at_rhs.php'

Done when

• Repro stderr empty on VM/JIT; stdout ok
• Bare @$undef; and other already-green @ forms unchanged
• Compliance .phpt under test/compliance/cases/language/
• php-src-strict; no php-compiler-strict shortcut

Related

• Closed Language: @ error-control operator — JIT/AOT native silence (phase 2 of #3546) #4070 (JIT/AOT @ silence phase 2) — does not cover this assign+undefined CV case
• Closed Regression: error_get_last() NULL after @ on bare undefined variable read — Zend still records (ext/standard/basic_functions.c) #13587 (error_get_last after bare @ read) — different surface