analyzer: mago does not infer parameter types of closure arguments

[bendavies]

🐞 Describe the Bug

i think the following code procudes a false positive.
mago 1.0.0-alpha.7

🔄 Steps to Reproduce

mago analyse

⚙️ Configuration (mago.toml)

# Mago configuration file
# For more information, see https://mago.carthage.software/#/getting-started/configuration
php_version = "8.3.0"

[source]
paths = ["bin/", "src/", "test/"]
includes = ["vendor"]

[format]
print_width = 180
tab_width = 4
use_tabs = false
null_type_hint = "question"
always_break_named_arguments_list = false

📜 Command Output

 ./mago --version
mago 1.0.0-alpha.7

error[mixed-argument]: Invalid argument type for argument #1 of `Owsy\ReleaseTool\Github\Value\Repository::fromFullName`: expected `string`, but found `mixed`.
   ┌─ src/Github/Value/Repositories.php:22:13
   │
21 │           $instance->repositories = Vec\values(Vec\map($payload, static fn(array $payload): Repository => Repository::fromFullName(
   │ ╭─────────────────────────────────────────────────────────────────────────────────────────────────────────'
22 │ │             $payload['name'],
   │ │             ^^^^^^^^^^^^^^^^ Argument has type `mixed`
23 │ │             \array_key_exists('alias', $payload) ? $payload['alias'] : null,
24 │ │         )));
   │ ╰─────────' Arguments to this method are incorrect
   │
   = The type `mixed` is too general and does not match the expected type `string`.
   = Help: Add specific type hints or assertions to the argument value.

error[mixed-argument]: Invalid argument type for argument #2 of `Owsy\ReleaseTool\Github\Value\Repository::fromFullName`: expected `null|string`, but found `mixed`.
   ┌─ src/Github/Value/Repositories.php:23:13
   │
21 │           $instance->repositories = Vec\values(Vec\map($payload, static fn(array $payload): Repository => Repository::fromFullName(
   │ ╭─────────────────────────────────────────────────────────────────────────────────────────────────────────'
22 │ │             $payload['name'],
23 │ │             \array_key_exists('alias', $payload) ? $payload['alias'] : null,
   │ │             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Argument has type `mixed`
24 │ │         )));
   │ ╰─────────' Arguments to this method are incorrect
   │

📂 PHP Code Sample (If Applicable)

<?php

    /** @param array<int, array{name: string, alias?: ?string}> $payload */
    public static function fromPayload(array $payload): self
    {
        $instance = new self();

        $instance->repositories = Vec\values(Vec\map($payload, static fn(array $payload): Repository => Repository::fromFullName(
            $payload['name'],
            \array_key_exists('alias', $payload) ? $payload['alias'] : null,
        )));

        return $instance;
    }

🖥️ Operating System

macOS

📦 How did you install Mago?

Composer (composer require carthage-software/mago)

📝 Additional Context

No response

[azjezz]

This behavior is not a false positive but rather a known limitation in our current type inference engine.

Our analyzer takes the type hint array on your closure literally. It assumes the closure must be able to handle any arbitrary array. Since a generic array is not guaranteed to contain the key 'name', the analyzer correctly flags a potential runtime error.

Psalm and PHPStan perform more advanced inference in this context. They analyze the array passed to Vec\map and infer that the $payload parameter inside the closure will always have the shape array{name: string, alias?: ?string}.

This is on our roadmap. I plan to ship it before our scheduled beta release next month.

As a workaround, you can resolve this by explicitly telling the analyzer the expected array shape using a @param docblock on the closure:

<?php

    /** @param array<int, array{name: string, alias?: ?string}> $payload */
    public static function fromPayload(array $payload): self
    {
        $instance = new self();

        $instance->repositories = Vec\values(Vec\map(
            $payload,
            /**
             * @param array{name: string, alias?: ?string} $payload
             */
            static fn(array $payload): Repository => Repository::fromFullName(
              $payload['name'],
              $payload['alias'] ?? null,
            ),
          ));

        return $instance;
    }