Investigate an assertion error in zend_string_destroy

[lisachenko]

Test suite fails in PHP 7.4.0RC3 debug build with message:

php-src/Zend/zend_variables.c:64: zend_string_destroy: Assertion `!(zval_gc_flags((str)->gc.u.type_info) & (1<<6))' failed.

Need to fix this assertion error.

[lisachenko]

I don't know ways to debug this issue, it's too complex right now.

I have a guess, that I'm using immutable strings from PHP. For example, immutable method names in tests and steal pointer to them to use in misc areas of code instead of crafting zend_string entry by hand. Probably, at the end of request GC tries to clean something (hashtable?) and assertion fails.

[lisachenko]

Should be fixed

[lisachenko]

Verified independently against the current codebase — confirming this stays closed.

Fix confirmed present and effective on both supported branches:

• ReferenceCountedTrait::incrementReferenceCount()/decrementReferenceCount() now throw on immutable payloads (interned strings, immutable arrays, shared-memory data) instead of mutating them.
• releaseReference() no-ops entirely for immutable/interned payloads, and only invokes the engine's own rc_dtor_func at refcount zero for non-persistent, non-immutable payloads — mirroring zend_string_release_ex's GC_IMMUTABLE guard that the original assertion was tripping.
• StringEntry's constructor skips add-ref for interned strings up front (second independent guard layer).
• Landed in 8e017a2 (fix(core): guard refcount mutation against immutable payloads and underflow) on branch 8.4, and already cascaded to master (PHP 8.5) via the automated merge-up (PR merge: cascade 8.4 into master (windows x64, resolved) #182, commit 2c70d43) — 8e017a2 is confirmed an ancestor of origin/master.

Verified on both PHP 8.4 and 8.5:

• Branch 8.4 (PHP 8.4) and master (PHP 8.5) both carry the fix.
• Both branches' tests-internal-debug CI job (a --enable-debug PHP build built specifically to surface Zend assertion failures like this one) is green on their current HEAD — 8.4@8419047 and master@4195cef.
• StringEntryOwnershipTest exercises interned-string release semantics directly.

No further code changes needed — closing confirmed as correct.

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