wrongly reporting error on non existing array keys

[quazardous]

Bug report

PPHStan is reporting error on non existing array keys.

Code snippet that reproduces the problem

<?php declare(strict_types = 1);

/**
* @return array<string, mixed>
*/
function foo(): array
{
	// something from elsewhere (not in the scope of PHPStan)
	return [
                // removing or keeping those lines does/should not change the reporting
		'foo' => [
			'bar' => true,
		]
        ];
}

$data = foo();
$data = $data['foo'] ?? []; // <<< removing this line suppress the error
$data += [
	'default' => true,
];
foreach (['formatted'] as $field) {
	$data[$field] = empty($data[$field]) ? false : true;
}

$bar = $data['bar'];

https://phpstan.org/r/f765334e-f883-4721-a742-7ea798cf9d4c

Expected output

No error

[ondrejmirtes]

Added dumped types to see where it goes wrong: https://phpstan.org/r/2a1fef8b-0e9e-4d3c-bead-ab21416254be (after the += operator)

[quazardous]

maybe it's not an "wrong" error (it depends on the confidence you have in the returned data)

// no error with
$data = (array)($data['foo'] ?? []);

[phpstan-bot]

@quazardous After the latest push in 1.8.x, PHPStan now reports different result with your code snippet:

@@ @@
-26: Offset 'bar' does not exist on array{formatted: bool}.
+No errors

[phpstan-bot]

@ondrejmirtes After the latest push in 1.8.x, PHPStan now reports different result with your code snippet:

@@ @@
 18: Dumped type: array<string, mixed>
 20: Dumped type: mixed
-24: Dumped type: *ERROR*
-28: Dumped type: array{formatted: bool}
-30: Offset 'bar' does not exist on array{formatted: bool}.
+24: Dumped type: non-empty-array
+28: Dumped type: hasOffsetValue('formatted', bool)&non-empty-array

Full report

Line	Error
18	Dumped type: array<string, mixed>
20	Dumped type: mixed
24	Dumped type: non-empty-array
28	Dumped type: hasOffsetValue('formatted', bool)&non-empty-array

[ondrejmirtes]

@staabm Regression test please.

[github-actions]

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