Keep the list flag when a list shape is intersected with an array type

[janedbal]

Closes phpstan/phpstan#15391

in_array() narrowing drops the list flag from a list{...} shape that has two or more optional keys. This is a regression in 2.1.41 from 951d9e4 (#5067).

/**
 * @param list{0: 'x', 1?: 'a'|'b', 2?: 'a'|'b'} $l
 * @return list<string>
 */
function f(array $l): array
{
	if (!in_array('b', $l, true)) {
		return $l; // should return list<string> but returns array{0: 'x', 1?: 'a', 2?: 'a'}
	}

	return [];
}

TypeCombinator::intersect() rebuilds a ConstantArrayType through ConstantArrayTypeBuilder when the other side is an ArrayType. The builder marks each optional key as a possible non-list key, so the rebuilt shape is only "maybe a list".

• A subset of a list is a list. TypeCombinator::intersect() now intersects the rebuilt shape with AccessoryArrayListType when the source shape is a list.
• turbo-ext/src/TypeCombinator.cpp gets the same change.
• tests/PHPStan/Analyser/nsrt/bug-15391.php is the regression test. It fails without the change in TypeCombinator.php and passes with it.

— Claude

[phpstan-bot]

This pull request has been marked as ready for review.

[staabm]

//cc @SanderMuller

[staabm]

needs rebase. otherwise LGTM

[Copilot]

🟢 Approval recommended

The fix is focused, mirrored consistently, and backed by suitable regression coverage.

0 open findings

What changed in this PR

Fixes #15391 by preserving list semantics when intersecting list-shaped constant arrays with array types.

Changes:

• Retains the list flag during intersection rebuilding.
• Mirrors behavior in the Turbo extension.
• Adds regression coverage and updates Turbo compatibility.

File	Description
src/​Type/​TypeCombinator.php	Preserves list semantics after rebuilding shapes.
turbo-ext/​src/​TypeCombinator.cpp	Mirrors the PHP implementation.
tests/​PHPStan/​Analyser/​nsrt/​bug-15391.php	Covers narrowing, direct intersection, and loops.
src/​Turbo/​TurboExtensionEnabler.php	Updates the expected Turbo version.

🧠 Review effort: Balanced

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[staabm]

thank you!