Fix phpstan/phpstan#13227: Intersections using object shapes

[phpstan-bot]

Summary

Object shapes (object{ a: int }) could not be intersected with each other, causing @phpstan-type aliases like Type1 & object{ b: int } to report "Type alias contains unresolvable type." This PR adds support for merging object shapes in intersections.

Changes

• Added ObjectShapeType intersection merging in src/Type/TypeCombinator.php (placed before isSuperTypeOf checks to handle all cases)
• Properties from both shapes are combined; overlapping properties have their types intersected
• If an overlapping property's intersection results in NeverType, the entire intersection returns NeverType
• A property is optional in the result only if it's optional in both input shapes
• Properties are sorted by key (ksort) for deterministic output regardless of operand order
• Updated tests/PHPStan/Type/TypeCombinatorTest.php to expect merged object shape instead of NeverType for disjoint-property intersections
• Updated phpstan-baseline.neon to reflect additional instanceof ObjectShapeType usages

Root cause

TypeCombinator::intersect() had no special handling for two ObjectShapeType instances. When two object shapes with different properties were intersected (e.g., object{a: int} & object{b: int}), ObjectShapeType::isSuperTypeOf() returned no because each shape was missing properties from the other. This caused TypeCombinator to return an implicit NeverType, which the type alias validator flagged as unresolvable.

Test

Added tests/PHPStan/Analyser/nsrt/bug-13227.php with:

• Type1 & object{ b: int } where Type1 is object{ a: int } — verifies merge into object{a: int, b: int}
• object{ a: int, b?: string } & object{ b: string, c?: int } — verifies optional property handling (b becomes required, c stays optional)

Fixes phpstan/phpstan#13227

[VincentLanglet]

Need to be clarified first
phpstan/phpstan#13227 (comment)

[VincentLanglet]

Add test in TypeCombinatorTest for

• object{foo: int}&object{foo?: int}
• object{foo: int}&object{foo: int|null}
• object{foo: int}&object{foo?: int|null}
• object{foo: int}&object{bar?: int}
• object{foo: int}&object{foo?: string}

[phpstan-bot]

The make tests background task also completed successfully. All done — the commit with the 5 new test cases has been pushed.

[staabm]

should have a review from ondrej

[VincentLanglet]

should have a review from ondrej

I considered ok given the answer he gave on slack

I just added tons of tests

(and he can still review after merge)

[staabm]

I see 👍

[ondrejmirtes]

Three more things I'd like you to try:

1. Try to make each if/else block empty in the src/ diff change. Each one of them should make at least one TypeCombinatorTest fail.
2. I'd like to see what ObjectShapeType answers in isSuperTypeOf about other instances. Typically I test isSuperTypeOf implementations/changes through TypeCombinatorTest, but here you're hardcoding behaviour into TypeCombinator, so I'd like to see what happens in isSuperTypeOf separately. I'll explain it below.
3. You added a bunch of dataIntersect tests. What happens in dataUnion? What would make sense to happen?

So, about 2). For union, the rule is - type wins in normalization if it says isSuperTypeOf yes() about the other type. So mixed|int results in mixed.

For intersection, the rule is - type wins, if it says isSuperTypeOf maybe() about the other type (and the other type says yes()). So mixed&int results in int.

If isSuperTypeOf() answers no(), the result of intersection is NeverType.

I'd like you to look at the tests you wrote and verify that isSuperTypeOf answers according to the results you expect from TypeCombinator. Of course in some cases you're combining properties from two shapes into one shape so you can't say which shape "wins" in "isSuperTypeOf". In that case it's okay to return maybe() from both sides.

[VincentLanglet]

If intersection of Two objectShapes works, the Intersection of

new ObjectShapeType(['foo' => new IntegerType()], []),
new HasPropertyType('bar'),

should not gives NEVER but object{foo: int, bar: mixed}

[phpstan-bot]

The background make phpstan task also completed successfully with no errors. Everything is pushed.

[phpstan-bot]

I processed this review but have nothing to report.