Psalm type inference mixes values and types

[emmanuelGuiton]

Psalm type inference mixes values and types, leading to wrong behaviors as this snipped shows : https://psalm.dev/r/6bc69067cf
Could it be fixed ?

When juggling with types, the issue occurs quite often, always requiring work-arounds. It lead me to write additional tools such as the class hereafter for the sole purpose of deceiving Psalm type system.

class CollectionUtils
{
	/**
	 * Casts anything that extends a possibly-empty list of elements into a possibly-empty list of elements.
	 *
	 * @param array $array Original collection of elements
	 * @return array Possibly empty list of elements
	 *
	 * @psalm-template T
	 * @psalm-template C of list<T>
	 * @psalm-param C $array
	 * @psalm-return list<T>
	 * @psalm-pure
	 */
	public static function list(array $array): array
	{
		return $array;
	}

	/**
	 * Casts an array into a list
	 *
	 * @param array $array Original array of elements
	 * @return array List of elements
	 *
	 * @psalm-template T
	 * @psalm-template C of array<array-key, T>
	 * @psalm-param C $array
	 * @psalm-return list<T>
	 * @psalm-pure
	 */
	public static function arrayToList(array $array): array
	{
		/** @var list<T> $array */
		return $array;
	}
}

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/6bc69067cf

<?php

/**
 * @psalm-template T
 * @psalm-param array<string, mixed> $values
 * @psalm-param string $paramName
 * @psalm-param T $default
 * @psalm-return T
 */
function readParam(array $values, string $paramName, mixed $default): mixed {
    assert(array_key_exists($paramName, $values));
	/** @psalm-suppress MixedAssignment */
    $rawValue = $values[$paramName];
    if (is_null($rawValue)) {
        return $default;
    } else {
        $defaultType = gettype($default);
        if ($defaultType == 'object') {
            assert(is_object($default));
            if ($rawValue instanceof $default) {
                /** @var T $rawValue */
                return $rawValue;
            } else {
                throw new \InvalidArgumentException("Value of attribute '{$paramName}' does not match the required type '" . get_class($default) . "'.");
            }
        } else {
            if ($defaultType == gettype($rawValue)) {
                /** @var T $rawValue */
                return $rawValue;
            } else {
                throw new \InvalidArgumentException("Value of attribute '{$paramName}' does not match the required type '{$defaultType}'.");
            }
        }
    }
}

$values = ['string' => 'a', 'int' => 42];

$val = readParam($values, 'string', '');
assert('' != $val);
$zero = readParam($values, 'noInt', 0);
assert($zero == 0);

// Work-arounds :
$val = readParam($values, 'string', strval('')); //  using strval() to deceive Psalm's type inference
assert('' != $val);
$zero = readParam($values, 'noInt', intval(0)); //  using intval() to deceive Psalm's type inference
assert($zero == 0);

Psalm output (using commit cdceda0):

ERROR: DocblockTypeContradiction - 40:1 - Docblock-defined type '' for $val is always ~string()

ERROR: RedundantConditionGivenDocblockType - 42:1 - Docblock-defined type 0 for $zero is always =int(0)