Class template type on static method

[olsavmic]

Hi,
We encountered a similar issue to #4258 and #2751.

I see that some work has been done to avoid this issue as in 50fc50f but there is still an issue with @param annotation.

Example of the issue (and a simplified use-case) is shown here: https://psalm.dev/r/cdf35ba896

The exact same code is working in PHPStan: https://phpstan.org/r/bcf918eb-626f-40cf-8b08-cbfa588f7b1f

Is there any reason why class level template parameters are forbidden in the @param annotation or is it a bug?

It's not possible to replace it with

  /**
   * @template TT
   * @param list<TT> $enums
   * @return static
   */
public static function ...

As that would loosen the type checking between the Enum and MultiEnum class.

I actually found a workaround using @template TT of T annotation instead on the class methods and I'm fine with such solution if it's the expected way of doing it but I'd at least add it to the docs.
(Workaround: https://psalm.dev/r/62775eb03c)

Thank you!

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/cdf35ba896

<?php

class Enum {
    public function __construct(
        public int $val,
    ) {
    
    }
}

/** @template T of Enum */
interface MultiEnumWithPairInterface {
    
  /**
   * @param list<T> $enums
   * @return static
   */
  public static function createFromList(array $enums);
}

class MultiEnum {
    
	private int $value;
    
    /**
     * @param list<int> $values
     */
    public final function __construct(array $values) {
    	$this->value = array_reduce(
            $values,
            static fn(int $acc, int $val): int => $acc | $val, 
            0,
        );
    }
    
    /**
     * @return static
     */
    public static function createFromValue(int $val) {
        return new static([$val]);
    }
}


/** @template T */
trait MultiEnumWithPair {
    
  /**
   * @param list<T> $enums
   * @return static
   */
  public static function createFromList(array $enums) {
  		return static::createFromValue(1);
  }
  
  /**
   * @param int $data
   * @return static
   */
  public static abstract function createFromValue(int $val);
}

class EnumABC extends Enum {
}

class EnumDEF extends Enum {
}

/**
 * @template-implements MultiEnumWithPairInterface<EnumABC>
 */
class MultiEnumABC extends MultiEnum implements MultiEnumWithPairInterface {


    /**
     * @use MultiEnumWithPair<EnumABC>
     */
    use MultiEnumWithPair;
}

$a = MultiEnumABC::createFromList([new EnumDEF(1)]);

Psalm output (using commit 40b6860):

ERROR: InvalidArgument - 81:35 - Argument 1 of MultiEnumABC::createFromList expects list<T>, array{EnumDEF} provided

INFO: UnusedVariable - 81:1 - $a is never referenced or the value is not used

ERROR: UndefinedDocblockClass - 15:13 - Docblock-defined class or interface T does not exist

ERROR: UndefinedDocblockClass - 49:13 - Docblock-defined class or interface T does not exist

INFO: MixedInferredReturnType - 50:14 - Could not verify return type 'MultiEnumABC' for MultiEnumWithPair::createFromList

https://psalm.dev/r/62775eb03c

<?php

class Enum {
    public function __construct(
        public int $val,
    ) {
    
    }
}

/** @template T of Enum */
interface MultiEnumWithPairInterface {
    
  /**
   * @template TT of T
   * @param list<TT> $enums
   * @return static
   */
  public static function createFromList(array $enums);
}

class MultiEnum {
    
	private int $value;
    
    /**
     * @param list<int> $values
     */
    public final function __construct(array $values) {
    	$this->value = array_reduce(
            $values,
            static fn(int $acc, int $val): int => $acc | $val, 
            0,
        );
    }
    
    /**
     * @return static
     */
    public static function createFromValue(int $val) {
        return new static([$val]);
    }
}


/** @template T */
trait MultiEnumWithPair {
    
  /**
   * @template TT of T
   * @param list<TT> $enums
   * @return static
   */
  public static function createFromList(array $enums) {
  		return static::createFromValue(1);
  }
  
  /**
   * @param int $data
   * @return static
   */
  public static abstract function createFromValue(int $val);
}

class EnumABC extends Enum {
}

class EnumDEF extends Enum {
}

/**
 * @template-implements MultiEnumWithPairInterface<EnumABC>
 */
class MultiEnumABC extends MultiEnum implements MultiEnumWithPairInterface {


    /**
     * @use MultiEnumWithPair<EnumABC>
     */
    use MultiEnumWithPair;
}

$a = MultiEnumABC::createFromList([new EnumDEF(1)]);

Psalm output (using commit 40b6860):

ERROR: InvalidArgument - 83:35 - Argument 1 of MultiEnumABC::createFromList expects list<EnumABC>, array{EnumDEF} provided

INFO: UnusedVariable - 83:1 - $a is never referenced or the value is not used