Language: never in union types — Unknown Op\Type\Union_ instead of Zend compile fatal (pairs #6967)

[PurHur]

Category

language · php-src-strict

Problem

Using never inside a union type (int|never, function f(int|never $x)) must be rejected at compile time with Zend's message:

never can only be used as a standalone type

This compiler dies earlier with Unknown Op\Type provided: PHPCfg\Op\Type\Union_ — same abort as general union regression (#7327), but never-in-union needs an explicit guard so workers do not confuse it with scalar union lowering.

Standalone never (function f(): never, never $p) must keep compiling.

php-src reference

• php/php-src Zend/zend_compile.c — zend_compile_type() never-in-union check
• php/php-src Zend/zend_type.c

Repro

test/repro/never_union_property.php:

<?php
class C {
    public int|never $x;
}
echo "ok\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php bin/vm.php test/repro/never_union_property.php 2>&1 | head -1
php -r "class C { public int|never \$x; }" 2>&1 | head -1   # PHP 8.x reference when available
'

Engine	Message
Zend	never can only be used as a standalone type
VM	Unknown Op\Type\Union_ ❌

Also verify parameter declarations: function f(int|never $x).

Scope (this repo)

Path	Work
lib/Compiler.php	Before union CFG lowering: scan type arms for Never_; throwCompileError('never can only be used as a standalone type')
Tests	test/compliance/cases/language/never_union_type.phpt (property + parameter)

Coordinate with #7327 scalar union lowering — this issue is the never-specific guard + message even if union compile is fixed separately.

Done when

• Repro exits 255 with exact Zend message (not Unknown Op\Type\Union_)
• Standalone never types still compile
• ./script/ci-fast.sh --filter never_union_type green

Related

• Language: never type in declared property unions — Unknown Op\\Type\\Union_ instead of Zend compile fatal #6967 (closed) · Language: scalar union types — compile abort Unknown Op\Type\Union_ (regression vs #6850/#6833) #7327 scalar unions · Language: never return type #1358 standalone never · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: worker-lane-a — starting this run

[PurHur]

Merged via #7336.

Verification

• never in union (int|never property/parameter): exits 255 with never can only be used as a standalone type (matches Zend), not Unknown Op\Type\Union_.
• Standalone : never return types compile again after completing the php-types-never overlay (Type::fromTypeDecl(CfgType\Never_) + fromDecl('never')).
• ./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./vendor/bin/phpunit --filter "NeverUnionTypeTest|BootstrapPhpTypesThrowExprPatchTest|never_union_type"' → OK (7 tests, 16 assertions).

PHP implementation: union guard in lib/Compiler.php (assertNeverIsStandaloneType); type lowering via script/apply-patches.sh never overlay on vendor/ircmaxell/php-types/lib/PHPTypes/Type.php.