Support reduced type inferring from Collection::reduce

[laurentmuller]

Plugin should add capability to infer reduced type from Collection::reduce based on assertions in a callback, similarly as Psalm currently does for array_reduce.

This is the the same as #58.

This is the current annotation: https://github.com/doctrine/collections/blob/b1f7c33ebb2d73a4860d6b65a11b9662b9904ebd/src/ReadableCollection.php#L241

For example, the following code must not raise any error:

class Item {
    public float $value = 0.0;
}

/** 
 * @param Collection<array-key, Item> $collection
 */
function foo(Collection $collection): float {
    return $collection->reduce(
        fn (float $carry, Item $item): float => $carry + $item->value,
        0.0
    );
}

See example: https://psalm.dev/r/80735e2f8d

The Collections.phpstub file must updated to reflect changes.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/80735e2f8d

<?php
/**
 * @psalm-template TKey of array-key
 * @psalm-template T
 */
interface Collection
{
   /**
     * Applies iteratively the given function to each element in the collection,
     * so as to reduce the collection to a single value.
     *
     * @psalm-param Closure(TReturn|TInitial, T):TReturn $func
     * @psalm-param TInitial $initial
     *
     * @psalm-return TReturn|TInitial
     *
     * @psalm-template TReturn
     * @psalm-template TInitial
     */
    public function reduce(Closure $func, mixed $initial = null): mixed;
}

class Item {
    public float $value = 0.0;
}

/** 
 * @param Collection<array-key, Item> $collection
 */
function foo(Collection $collection): float {
    return $collection->reduce(
        fn (float $carry, Item $item): float => $carry + $item->value,
        0.0
    );
}

Psalm output (using commit 16b24bd):

No issues!

[laurentmuller]

It's correct. But no definition exist for the reduce() function in the collections stub.

[laurentmuller]

FYI:

Please see how is implemented in phpstan/phpstan-doctrine v1.5.5