Simulate issset for null coalesce operator

[rajyan]

fixes phpstan/phpstan#4885
fixes phpstan/phpstan#5304
fixes phpstan/phpstan#5337

[rajyan]

Several thing to consider and fix.
The test fails because the behaviour for coalesce and isset ternary is slightly different with undefined variables.
Although

isset($a) ? $a : null;
isset($a->b) ? $a->b : null;

$a ?? null;
$a->b ?? null;

are all valid (no errors, but kind of buggy), currently PHPStan throws an error Undefined variable: $a for isset ternary while coalesce dosen't.

Also, it may be misleading, if IssetRule errors occur by coalesce.

[rajyan]

I should separate the PR for 6870

[rajyan]

memo phpstan/phpstan#3283
phpstan/phpstan#6026

[rajyan]

5 errors in tests

1. From 71c51e4

• The logic of lookForEnterVariableAssign should be moved to Isset_ (and also Empty_)
• Maybe related?
  • Property is never read, only written with null coalescing operator phpstan#6107
  • Wrong processing a null coalescing in function/method argument phpstan#3659
  • False positive with null coalescing operator phpstan#6026
  • False positive in Property Class::$property is never read, only written-rule when using empty() phpstan#5971

2, 3, 5. Fixes phpstan/phpstan#6809 and some others but conflicting with the current test case
4. Should be fixed in Isset

• created an issue Cannot access property on string not reported in isset phpstan#6899

[rajyan]

The failures in the tests looks good to me, but it's definitely a breaking change.
Two differences of Coalesce and Isset_ now (before this PR)

1. PropertyFetch in isset is not considered as read
   

   phpstan-src/tests/PHPStan/Rules/DeadCode/data/bug-5337.php

   Lines 17 to 27 in f6c6c5e

   	class Foo
   	{
   	private string $field;
   	public function __construct()
   	{
   	if (isset($this->field)) {}
   	}
   	}

   
   This reports Property Bug5337\Foo::$field is unused for isset, but something like $this->field ?? false would say only read.

By the way, there is a bug in coalesce too, reported in phpstan/phpstan#5971 (comment)
which

$this->field->prop ?? false

would not be recognized as read for property $field.

2. Dynamic property in isset is not reporting undefined property

As explained in phpstan/phpstan#6809 (comment)

This commit cf0059e
would solve the first problem (leaving the bug phpstan/phpstan#5971 (comment)), and report undefined property for dynamic property for the second one (which makes it more strict, but maybe too strict for some usecases?).

[rajyan]

I think first one should be fixed, but not sure about the second one.
As shown in
https://phpstan.org/r/56de90d5-b01b-42fd-ab31-912e2a3f6d79
dynamic property errors in level 0 anyway, so maybe in reporting in isset too is applicable.

[ondrejmirtes]

Please see my thinking about this: phpstan/phpstan#6809 (comment)

I don't want BC breaks around this for analysis on PHP <= 8.1. We can do something more ambitious and strict for PHP 8.2 and objects that do not allow dynamic properties, but right now, there are too many test failures :)

[rajyan]

@ondrejmirtes
Thank you for your comment. I'm working on now to solve the first problem (which is a bug I think), while leaving the dynamic property behavior as is. I'll mark this PR ready after the tests are passed!

[ondrejmirtes]

Superseded by #1192