array_map((a, b) => c), a, b) fails to infer the type of b in the closure

[Ocramius]

Typically, array_map() is used with two parameters, one is the closure mapping the values, and one is the foldable passed to that closure.

When array_map(function ($a, $b) { return $c; }, $as, $bs) is used, then the type of $b fails to be inferred as the type of $bs items: https://psalm.dev/r/cdabfb49ce

When declaring the type of $b explicitly, the errors obviously go away: https://psalm.dev/r/c5f1c38c50

The code is obviously over-simplified: the reason why this issue exists, is because $b is often a complex nested structure.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/cdabfb49ce

<?php

/** @psalm-return array<array<string, string>> */
function functionsToBeTested() : array
{
  $as = ['key'];
  $bs = ['not important'];
  
    return array_map(
        /** @psalm-suppress MissingClosureParamType closure type is omitted to show missing inference */
        function (string $a, $b) : array {
            return [$a => $b];
        },
        $as,
        $bs
    );
}

Psalm output (using commit b439a57):

INFO: MixedReturnTypeCoercion - 9:12 - The type 'list<non-empty-array<string, mixed>>' is more general than the declared return type 'array<array-key, array<string, string>>' for functionsToBeTested

INFO: MixedReturnTypeCoercion - 3:19 - The declared return type 'array<array-key, array<string, string>>' for functionsToBeTested is more specific than the inferred return type 'list<non-empty-array<string, mixed>>'

https://psalm.dev/r/c5f1c38c50

<?php

/** @psalm-return array<array<string, string>> */
function functionsToBeTested() : array
{
  $as = ['key'];
  $bs = ['not important'];
  
    return array_map(
        function (string $a, string $b) : array {
            return [$a => $b];
        },
        $as,
        $bs
    );
}

Psalm output (using commit b439a57):

No issues!

[Ocramius]

Actual example from the code in the downstream project: https://psalm.dev/r/f5715acb09

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/f5715acb09

<?php

final class BetterReflectionFunctionAbstract
{
}

final class BetterReflectionClass
{
    public function getMethod(string $method) : BetterReflectionFunctionAbstract
    {
        throw new \Exception('ignore');
    }
}

final class ClassReflector
{
    public function reflect(string $className) : BetterReflectionClass
    {
        throw new \Exception('ignore');
    }
}

final class FunctionReflector
{
    public function reflect(string $functionName) : BetterReflectionFunctionAbstract
    {
        throw new \Exception('ignore');
    }
}

/**
 * @psalm-return array<string, array{
 *   0: BetterReflectionFunctionAbstract,
 *   1: BetterReflectionFunctionAbstract,
 *   2: list<string>
 * }>
 */
function functionsToBeTested() : array
{
    $fromClassReflector = new ClassReflector();
    $toClassReflector   = new ClassReflector();
    $fromReflector      = new FunctionReflector();
    $toReflector        = new FunctionReflector();

    $functions = [
        'orderChanged'                       => [
            '[BC] CHANGED: Default parameter value for for parameter $a of orderChanged() changed from 1 to 3',
            '[BC] CHANGED: Default parameter value for for parameter $c of orderChanged() changed from 3 to 1',
        ],
    ];

    return array_merge(
        array_combine(
            array_keys($functions),
            array_map(
                function (string $function, array $errorMessages) use ($fromReflector, $toReflector) : array {
                    return [
                        $fromReflector->reflect($function),
                        $toReflector->reflect($function),
                        $errorMessages,
                    ];
                },
                array_keys($functions),
                array_values($functions)
            )
        ),
        [
            'C::changed1' => [
                $fromClassReflector->reflect('C')->getMethod('changed1'),
                $toClassReflector->reflect('C')->getMethod('changed1'),
                [
                    '[BC] CHANGED: Default parameter value for for parameter $a of C::changed1() changed from 1 to 2',
                ],
            ]
        ]
    );
}

Psalm output (using commit b439a57):

ERROR: InvalidReturnStatement - 52:12 - The type 'non-empty-array<string(C::changed1)|string(orderChanged), array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: non-empty-array<array-key, mixed>}>' does not match the declared return type 'array<string, array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: list<string>}>' for functionsToBeTested

ERROR: InvalidReturnType - 32:18 - The declared return type 'array<string, array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: list<string>}>' for functionsToBeTested is incorrect, got 'non-empty-array<string, array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: non-empty-array<array-key, mixed>}>'

[muglug]

For whatever reason the @psalm-suppress confuses things, when it's removed everything works: https://psalm.dev/r/3ca580553f

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/3ca580553f

<?php

/** @psalm-return array<array<string, string>> */
function functionsToBeTested() : array
{
  $as = ['key'];
  $bs = ['not important'];
  
    return array_map(
        function (string $a, $b) : array {
            return [$a => $b];
        },
        $as,
        $bs
    );
}

Psalm output (using commit 5f4d797):

No issues!

[Ocramius]

Uhh, something else happened too: if you see the comment above (about the real-world use-case), @psalm-github-bot found:

Psalm output (using commit b439a57):

ERROR: InvalidReturnStatement - 52:12 - The type 'non-empty-array<string(C::changed1)|string(orderChanged), array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: non-empty-array<array-key, mixed>}>' does not match the declared return type 'array<string, array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: list<string>}>' for functionsToBeTested

ERROR: InvalidReturnType - 32:18 - The declared return type 'array<string, array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: list<string>}>' for functionsToBeTested is incorrect, got 'non-empty-array<string, array{0: BetterReflectionFunctionAbstract, 1: BetterReflectionFunctionAbstract, 2: non-empty-array<array-key, mixed>}>'

Now it no longer reports anything

[muglug]

Now it no longer reports anything

Yeah, because now it's inferring the types properly, right? Or is the code incorrect?

[Ocramius]

No, the code is correct, I'm just wondering what changed on this side meanwhile (the snippet wasn't changed)

[muglug]

That's due to this commit: 9115ffd2

Psalm now has a better idea the array type than it did before, so it uses that instead of the array param type.

[Ocramius]

\o/ thanks!