Analyse constant xpath expression

[mvorisek]

Feature request

Like https://phpstan.org/r/9c6ac5fc-d975-473e-ab7c-dc95ece0c6b1 (issue #2046) - DOMDocument::getElementsByTagName() always return collection of DOMElement.

#7681 is valid issue, xpath expression in the repro below always returns collection of DOMElements.

This is a feature request to analyse constant string xpath input to narrow the return type based on it. Per [1] the result is also never false as long as the expression is valid.

repro https://phpstan.org/r/6f02c158-3f87-4c04-b4d5-0dd5ee322ce7

functional repro: https://3v4l.org/l2B9Hq/rfc#vgit.master

[1] https://www.php.net/manual/en/domxpath.query.php#refsect1-domxpath.query-returnvalues

[phpstan-bot]

@mvorisek After the latest push in 1.11.x, PHPStan now reports different result with your code snippet:

@@ @@
-20: Cannot call method getAttribute() on DOMNode|null.
+ 7: Property Foo::$content is never written, only read.
+ 9: Method Foo::doFoo() has no return type specified.

Full report

Line	Error
7	Property Foo::$content is never written, only read.
9	Method Foo::doFoo() has no return type specified.