Validation<T> is impossible to infer for failures

[ilario-pierbattista]

    /**
     * @psalm-template T
     * @psalm-param mixed $value
     * @psalm-param Context $context
     * @psalm-param string|null $message
     * @psalm-return ValidationFailures<T>
     *
     * @param mixed $value
     */
    public static function failure($value, Context $context, ?string $message = null): self
    {
        return self::failures(
            [new VError($value, $context, $message)]
        );
    }

This constructor will never infer correctly Validation<T>.

[Jean85]

Wouldn't it be technically a ValidationFailure<never>? As a bottom type it should match with everything... Or not?

[ilario-pierbattista]

Something like that @Jean85.

I think I've introduced a design error attempting to carrying on information about the decoder target type also in case of error.

In io-ts, the decode function gives an Either<Errors, T>.
ValidationFailure<T> is not isomorphic with Left<Errors>.