Language: instanceof with union types — (A|B) RHS (Zend zend_type.c parity)

[PurHur]

Category

language

Problem

PHP 8.0+ allows instanceof against a union of class/interface names: $obj instanceof (A|B). This compiler treats the parenthesized union as a bogus constant fetch and fails at runtime.

php-src reference

• Zend/zend_compile.c — zend_compile_instanceof() / instanceof_list handling
• Zend/zend_type.c — zend_type_apply_mask(), union type lists
• Zend/zend_execute.c — ZEND_INSTANCEOF, instanceof_function_ex()

Repro

<?php
interface A {}
interface B {}
class C implements A, B {}
var_dump((new C) instanceof (A|B));

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php repro.php'
php repro.php   # Zend: bool(true)

This compiler (May 2026): LogicException: Unknown constant fetch
Zend PHP: bool(true)

Scope (this repo)

Layer	Files
php-cfg / parser	Union type in instanceof RHS if not already emitted
Compiler	lib/Compiler.php — compileExpr for Expr_Instanceof
VM	lib/VM.php — walk implemented interfaces/classes for union members
JIT	lib/JIT.php — after VM PHPT green
Tests	test/compliance/cases/language/instanceof_union.phpt

Done when

• Repro prints bool(true) on VM; false when object implements neither arm
• Compile error for invalid union members (Zend subset)
• ./script/ci-fast.sh --filter instanceof_union green
• docs/capabilities-syntax.md row or note for union instanceof (regenerate matrix script)

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter instanceof_union'

Related

• Language: DNF types — union of intersections (PHP 8.2) #3094 DNF type declarations (distinct from instanceof RHS)
• Language: instanceof operator for class checks #138 / Compiler: Class inheritance (extends) and interfaces #101 interface instanceof baseline

[PurHur]

claim: worker-lane-c — starting this run