Wrong LessSpecificReturnStatement and MoreSpecificReturnType

[thelmuxkriovar]

In some code I wrote that 2 errors would show up no matter what I did, LessSpecificReturnStatement and MoreSpecificReturnType, so I noticed that psalm doesn't know when a list contains for certain only strings.
Here's some example code that shows the issue https://psalm.dev/r/657911d214

$metadata['tags'] = array_filter($metadata['tags'], fn($tag) => is_string($tag));

ensures without any doubt that $metadata['tags'] only contains strings.

What's interesting is that

$metadata['tags'] = array_map((fn($tag) => (string) $tag), $metadata['tags']);

works. However it's not ideal as it's not filtering anything, just string casting.

Maybe psalm doesn't consider array_filter?

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/657911d214

<?php
/**
* @psalm-return array{something: int, tags: list<string>}
*/
function testFunc() : array {
 	$metadata = ['something' => rand()];
  	// imagine a bunch of code with a bunch of checks and filters including:
	$metadata['tags'] = array_filter($metadata['tags'], fn($tag) => is_string($tag));
	$metadata['tags'] = array_values($metadata['tags']);
	return $metadata;
}

Psalm output (using commit 504de0a):

ERROR: InvalidArrayOffset - 8:35 - Cannot access value on variable $metadata using offset value of 'tags', expecting 'something'

INFO: MissingParamType - 8:57 - Parameter $tag has no provided type

INFO: MixedArgument - 8:35 - Argument 1 of array_filter cannot be mixed, expecting array<array-key, mixed>

INFO: LessSpecificReturnStatement - 10:9 - The type 'array{something: int, tags: list<mixed>}' is more general than the declared return type 'array{something: int, tags: list<string>}' for testFunc

INFO: MoreSpecificReturnType - 3:17 - The declared return type 'array{something: int, tags: list<string>}' for testFunc is more specific than the inferred return type 'array{something: int, tags: list<mixed>}'

[SignpostMarv]

I believe it's tripping up because $metadata['tags'] doesn't exist, so is probably defaulting to mixed in it's absence.

see https://psalm.dev/r/1f8c1c193c

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/1f8c1c193c

<?php
/**
* @psalm-return array{something: int, tags: list<string>}
*/
function testFunc() : array {
 	$metadata = ['something' => rand(), 'tags' => ['foo', 1, 2.3]];
  	// imagine a bunch of code with a bunch of checks and filters including:
	$metadata['tags'] = array_filter($metadata['tags'], fn($tag) => is_string($tag));
	$metadata['tags'] = array_values($metadata['tags']);
	return $metadata;
}

Psalm output (using commit 504de0a):

No issues!

[thelmuxkriovar]

Sorry! The fact that it's missing is only an issue with my test code, the actual code loads a bunch of things from a yaml file, amongst which is 'tags', I even have a check to create an empty array it if it's missing

[SignpostMarv]

does it make a difference in your local code if you $metadata['tags'] = array_filter($metadata['tags'], 'is_string'); ?

[thelmuxkriovar]

Surprisingly it does! I expected it to make no difference, but it absolutely does

[muglug]

Did you try on latest master?

[muglug]

Pretty sure this is a dupe of #2627 – I'll release soon.