Userland filter function

[Baptouuuu]

Psalm is able to correctly determine the return type of an array after a call to array_filter. If we use a templated collection class that have a filter method (with the same logic as array_filter) Psalm is not able to determine the correct template of the container after the call to filter.

Example: https://psalm.dev/r/9cab8b9bdc

It would be interesting to have a way to declare this behaviour but I'm not sure how the syntax would look like.

[orklah]

array_filter is a know function for which we defined a special behaviour here:

psalm/src/Psalm/Internal/Provider/ReturnTypeProvider/ArrayFilterReturnTypeProvider.php

Line 36 in 9d22508

class ArrayFilterReturnTypeProvider implements FunctionReturnTypeProviderInterface

However, the method "filter" of a random object doesn't have this particular behaviour applied by Psalm.

If it's part of a framework, you could consider creating a plugin to recycle this behaviour when you spot the desired method in an object

[AndrolGenhald]

Not currently possible, but it would probably be possible if templates and closures were improved. The syntax would be a bit verbose though. See #7944 and this example (not working, but how it probably could work in the future).