phpstan-src Fix !isset() with ArrayDimFetch

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the current 1.10.x handles the !isset() context for variables only. it works only correct for !isset($var) and its implications on the variable.

with this PR we add support for !isset($var['abc']) which means

we handle implications on $var's array-shape based on the $var['abc']-offset type (based on nullability and optional/non-optional offset state)

with this PR we know when

offsets can only be null or non-null in true/falsey-context
offsets may or will not exist in falsey-context
on array-shapes with just a single offset we know about the certainty implications on the var in falsey-context

the newly added tests in tests/PHPStan/Analyser/data/falsy-isset.php best reflect the new type inference implications.

closes https://github.com/phpstan/phpstan/issues/9908 closes https://github.com/phpstan/phpstan/issues/9426 closes https://github.com/phpstan/phpstan/issues/8724 closes https://github.com/phpstan/phpstan/issues/5128

Nov 30 '23 13:11 staabm

the remaining error is strange

Offset 'input' does not exist on array{input: Bug8724b\Input}|array{label: string}.

I have not yet an idea about it... but maybe we should even expect this error?

type-wise the offset label always exists, which means the null-coalescing is unnecessary and the code right to ?? is actually dead code..?

/**
 * @param array{label:string}|array{input:Input} $data
 */
function test(array $data): void
{
	$label = $data['label'] ?? $data['input']->getLabel();
}

Nov 30 '23 14:11 staabm

This pull request has been marked as ready for review.