Fix phpstan/phpstan#14407: !in_array with enum values incorrectly narrows to *NEVER*

[phpstan-bot]

Summary

When !in_array($x, $arr) is used where $x is an enum case and $arr is a non-empty array that may contain different enum cases in different branches (e.g., array{A}|array{B}), PHPStan incorrectly narrowed $x to *NEVER*. This happened because the type specifier used the full union of all possible array values for narrowing, even though no single value was guaranteed to be present in every array variant.

Changes

• Modified src/Type/Php/InArrayFunctionTypeSpecifyingExtension.php to compute a "guaranteed value type" in the false context by intersecting the iterable value types of all union members of the array type
• For union array types like array{A}|array{B}, the intersection of value types A and B is never, so no narrowing occurs
• For non-union array types like array{A, B}, behavior is unchanged since there's only one variant

Root cause

InArrayFunctionTypeSpecifyingExtension used $arrayType->getIterableValueType() for narrowing in the false context. For a UnionType of arrays, getIterableValueType() returns the union of all possible values across all variants. But in the false context (!in_array), we can only safely remove values from the needle type that are guaranteed to be in every possible array variant. The fix computes this guaranteed type by intersecting value types across union members.

Test

Added tests/PHPStan/Analyser/nsrt/bug-14407.php with three test cases:

1. Union array array{A}|array{B} - needle should NOT be narrowed to *NEVER*
2. Constant array array{A, B} - needle should correctly be narrowed to *NEVER*
3. Possibly-empty array (from comment in issue) - no narrowing should occur

Fixes phpstan/phpstan#14407

[VincentLanglet]

For performance use a single intersect call at the end of the foreach

[phpstan-bot]

Done. The change collects all inner value types into an array and passes them to a single TypeCombinator::intersect(...$innerValueTypes) call instead of intersecting incrementally in the loop, as requested by VincentLanglet. Tests and static analysis both pass.

[VincentLanglet]

Add test for union of constant array with optional keys.

/**
 * @param 'a'|'b'|'c' $x
 * @param array{a: 'a', c: 'c'}|array{a?:'a', b: 'b'} $a
 */
function test($x, $a): void
{
	assertType("array{a: 'a', c: 'c'}|array{a?: 'a', b: 'b'}", $a);
	if (!\in_array($x, $a, true)) {
		assertType("'a'|'b'|'c'", $x);
	}
}

[phpstan-bot]

Done. The changes:

1. Test added: Union of constant arrays with optional keys (array{a: 'a', c: 'c'}|array{a?: 'a', b: 'b'}) - verifies no narrowing occurs since 'a' from the optional key isn't guaranteed to be present.

2. Fix: When computing guaranteed values for !in_array narrowing, constant arrays now exclude values from optional keys. Uses getConstantArrays() (not instanceof) and isOptionalKey() to filter. For the test case, the second variant's guaranteed value is only 'b' (not 'a'|'b'), so intersecting with 'a'|'c' yields never, preventing incorrect narrowing.

[VincentLanglet]

All this computation is only useful if we're in the case

count($needleType->getFiniteTypes()) > 0
&& $arrayType->isIterableAtLeastOnce()->yes()

So refactor to avoid the unnecessary computation

[phpstan-bot]

Done. The refactoring moves the expensive $narrowingValueType computation (intersecting inner value types) inside the elseif branch where it's actually needed — guarded by count($needleType->getFiniteTypes()) > 0 && $arrayType->isIterableAtLeastOnce()->yes(). This avoids unnecessary computation when those preconditions aren't met. All tests and static analysis pass.

[VincentLanglet]

Simplify this with a dedicated private method to compute the narrowingValueType in the context false

[phpstan-bot]

Done. Extracted the narrowing value type computation into a private computeGuaranteedValueType() method, simplifying the specifyTypes() method. Tests (11708 passing) and static analysis (no errors) both pass.

[VincentLanglet]

With a computeNeedleNarrowingValue method you could write

$narrowingValue = $this->computeNeedleNarrowingValue(...);
if (null !== computeNeedleNarrowingValue) {
    ...
}

This method would return arrayValueType in context true, and so on

[phpstan-bot]

Background tests also completed successfully. All clear - the commit is pushed and both static analysis and tests pass.