Regression: SimpleXMLElement (bool) cast — empty/"0" elements false; empty($missingVar) false (ext/simplexml/sxe.c)

[PurHur]

Category

stdlib · php-src-strict · SimpleXML scalar cast (pillar 4 / live-node adjacent)

Problem

Zend sxe_object_cast_ex treats a present element as boolean true even when its text is empty or "0". Only a missing/blank node property is false. After $z = $xml->missing, empty($z) is true on Zend.

VM (bool) follows ordinary string-truthiness of the text content (empty/"0" → false), and empty($z) after assigning a missing child is false.

Distinct from #19707 (empty($xml->child) property-fetch path — already green for empty($xml->z)).

Probed 2026-07-23 on master VM vs host Zend 8.2.32 (./script/docker-exec.sh). Use parentheses: (bool)($xml->a) (cast binds tighter than ->).

Repro ($xml = simplexml_load_string('<r><a/><b>0</b><d>x</d></r>'))	Zend 8.2+	VM (2026-07-23)
(bool)($xml->a) empty element	true	false
(bool)($xml->b) text "0"	true	false
(bool)($xml->d) text "x"	true	true
(bool)($xml->z) missing	false	false
$z=$xml->z; empty($z)	true	false

php-src reference

• php/php-src ext/simplexml/simplexml.c — sxe_object_cast_ex (IS_FALSE / IS_TRUE / _IS_BOOL)
• Missing/blank node detection used by cast and empty() on an already-fetched SimpleXMLElement

PHP implementation target

• lib/VM/Variable.php (toBool) and/or ext/simplexml/VmSimpleXml.php — SimpleXMLElement object cast to bool per sxe_object_cast_ex (present element ⇒ true; blank/missing ⇒ false)
• Ensure empty($sxeVar) on an assigned missing-child view matches Zend (related blank-node check)
• JIT/AOT object-cast lowering must share the same rule; no new runtime/*.c logic

Repro

./script/docker-exec.sh -- bash -lc 'cat > /tmp/sxe_bool.php <<'\''PHP'\''
<?php
$xml=simplexml_load_string("<r><a/><b>0</b></r>");
var_export((bool)($xml->a)); echo "\n";
var_export((bool)($xml->b)); echo "\n";
$z=$xml->z; var_export(empty($z)); echo "\n";
PHP
php /tmp/sxe_bool.php; php bin/vm.php /tmp/sxe_bool.php'

Done when

• Table rows match Zend on VM (and JIT/AOT if in scope)
• Compliance .phpt under test/compliance/cases/simplexml/
• php-src-strict; no php-compiler-strict shortcut

[PurHur]

Maintainer gate snapshot (2026-07-23)

Filed from a live Zend-vs-VM probe run. Full maintainer note also attempted on #10533 (comments locked at 2500+).

Gate	Status	First symptom
inventory (release-readiness)	green	OK 6479/6479
spine coverage	green	OK
VM driver execute probe	green	OK
release-readiness --json	red	user_release_ready: no
north-star5-verify-fast	red	step 4f-m gen-0 lowering_source_fingerprint mismatch (#8713/#21905)
Open PRs	none	—

Pillar 1 trust gate is red until gen-0 manifest/driver fingerprint is refreshed.

[PurHur]

claim: worker-lane-B — starting this run

Pre-claim gates (2026-07-25):

• php script/bootstrap-inventory.php --check → OK 6541/6541
• release-readiness --json / bootstrap-selfhost-link → in progress (CI lock; prior note: north-star5-fast 4f-m fingerprint red on master, tracked by Gen-1+ #1492: committed gen-0 seed cannot be rebuilt — refresh OOMs at 48 GiB, 44 restamps since the blob last changed (script/bootstrap-refresh-gen0-sidecar.sh) #22642 / PR Bootstrap: unblock gen-0 spine refresh — docblock, ghost require, exclusive launcher (#22642) #22717 — not this lane)
• Eligible Lane B pick: Pillar 4 SimpleXML (bool) / empty($z) regression; no open PR; no prior claim:

[PurHur]

merged via #23126

Verification: Zend/VM issue repro identical (true/true/true/false/true); ./script/phpunit.sh --filter 'element_bool_cast|isset_child_property' → OK 4 tests; inventory OK 6541/6541.

Fix: VmSimpleXml::objectIsTruthy = php-src sxe_object_cast_ex(_IS_BOOL) — present node true (empty/"0" text included); missing named-child / empty root false. Wired in Variable::toBool + boolval::isTruthy.