Feature: use return type providers for inferred return types

[kkmuffme]

https://psalm.dev/r/90304e4579

Ideally psalm would correctly infer that $first and $second are identical

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/90304e4579

<?php

/**
 * @param array $a
 * @param array $b
 * @return array
 */
function foo( $a, $b ) {
    $tmp = array_merge( $a, $b );
    /** @psalm-trace $tmp */;
    return $tmp;
}

$y = array( 'foo' => 'bar' );
$z = array( 'hello' => 'world' );

$first = array_merge( $y, $z );
/** @psalm-trace $first */;

$second = foo( $y, $z );
/** @psalm-trace $second */;

Psalm output (using commit 4e17585):

INFO: Trace - 10:29 - $tmp: array<array-key, mixed>

INFO: Trace - 18:27 - $first: array{foo: 'bar', hello: 'world'}

INFO: Trace - 21:28 - $second: array<array-key, mixed>

[danog]

A long-time todo of mine, would really help in legacy codebases especially.

[kkmuffme]

Yes, but not only there, since the A&B annotation only works for object-like arrays, so documenting functions that merge 2 arrays with additional custom logic is currently impossible

[danog]

This would be a separate issue regarding template support for intersection of keyed arrays (#7600 is somewhat related), though it might be tricky to implement properly for usecases other than the simple "enhance" example mentioned in #7600 due to the different semantics of array_merge and array_replace.

[danog]

I've been planning to implement something really cool to infer literal types: automatic inlining of functions and full literal type inferring for pure native functions (I actually already submitted a PR once for this last feature #5723, might be worth to re-submit a slightly tweaked version...)

[weirdan]

Meanwhile you can do this: https://psalm.dev/r/662034762d

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/662034762d

<?php

/**
 * @template TK1 of array-key
 * @template TV1 of mixed
 * @template TK2 of array-key
 * @template TV2 of mixed
 * @param array<TK1,TV1> $a
 * @param array<TK2,TV2> $b
 * @return array<TK1|TK2,TV1|TV2>
 */
function foo( $a, $b ) {
    $tmp = array_merge( $a, $b );
    /** @psalm-trace $tmp */;
    return $tmp;
}

$y = array( 'foo' => 'bar' );
$z = array( 'hello' => 'world' );

$first = array_merge( $y, $z );
/** @psalm-trace $first */;

$second = foo( $y, $z );
/** @psalm-trace $second */;

Psalm output (using commit 6d03c32):

INFO: Trace - 14:29 - $tmp: array<(TK1:fn-foo as array-key)|(TK2:fn-foo as array-key), (TV1:fn-foo as mixed)|(TV2:fn-foo as mixed)>

INFO: Trace - 22:27 - $first: array{foo: 'bar', hello: 'world'}

INFO: Trace - 25:28 - $second: array<'foo'|'hello', 'bar'|'world'>

[kkmuffme]

@weirdan this doesn't work correctly if you have arrays with partially identical keys: https://psalm.dev/r/b1dd74bbf1

$second: array<'foo'|'hello', 'bar'|'world'>

is wrong, bc it should be (like $first correctly shows)

$second: array<'foo'|'hello', 'bar'>

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/b1dd74bbf1

<?php

/**
 * @template TK1 of array-key
 * @template TV1 of mixed
 * @template TK2 of array-key
 * @template TV2 of mixed
 * @param array<TK1,TV1> $a
 * @param array<TK2,TV2> $b
 * @return array<TK1|TK2,TV1|TV2>
 */
function foo( $a, $b ) {
    $tmp = array_merge( $a, $b );
    /** @psalm-trace $tmp */;
    return $tmp;
}

$y = array( 'foo' => 'bar', 'hello' => 'world' );
$z = array( 'hello' => 'bar' );

$first = array_merge( $y, $z );
/** @psalm-trace $first */;

$second = foo( $y, $z );
/** @psalm-trace $second */;

Psalm output (using commit 7869cb5):

INFO: Trace - 14:29 - $tmp: array<(TK1:fn-foo as array-key)|(TK2:fn-foo as array-key), (TV1:fn-foo as mixed)|(TV2:fn-foo as mixed)>

INFO: Trace - 22:27 - $first: array{foo: 'bar', hello: 'bar'}

INFO: Trace - 25:28 - $second: array<'foo'|'hello', 'bar'|'world'>

[weirdan]

The type is not wrong per se, but it's not as tight as it potentially could be. And key-value correspondence is lost too.

[kkmuffme]

Not really, bc the value can never be hello in this 2nd example https://psalm.dev/r/b1dd74bbf1

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/b1dd74bbf1

<?php

/**
 * @template TK1 of array-key
 * @template TV1 of mixed
 * @template TK2 of array-key
 * @template TV2 of mixed
 * @param array<TK1,TV1> $a
 * @param array<TK2,TV2> $b
 * @return array<TK1|TK2,TV1|TV2>
 */
function foo( $a, $b ) {
    $tmp = array_merge( $a, $b );
    /** @psalm-trace $tmp */;
    return $tmp;
}

$y = array( 'foo' => 'bar', 'hello' => 'world' );
$z = array( 'hello' => 'bar' );

$first = array_merge( $y, $z );
/** @psalm-trace $first */;

$second = foo( $y, $z );
/** @psalm-trace $second */;

Psalm output (using commit 7869cb5):

INFO: Trace - 14:29 - $tmp: array<(TK1:fn-foo as array-key)|(TK2:fn-foo as array-key), (TV1:fn-foo as mixed)|(TV2:fn-foo as mixed)>

INFO: Trace - 22:27 - $first: array{foo: 'bar', hello: 'bar'}

INFO: Trace - 25:28 - $second: array<'foo'|'hello', 'bar'|'world'>