validate typescript signature incorrect?

[nabati]

If you pass

const data: unknown  = 'some data from unknown source';
validate<Type>("stringSchema", unknownData);

you will always match the first overload, and the first overload is missing the async case.

Are you going to resolve the issue?
I can, if someone confirms that it's a valid issue.

[nabati]

https://github.com/ajv-validator/ajv/blob/master/lib/core.ts#L308-L339

[nabati]

Simplified example;

https://www.typescriptlang.org/play?#code/GYVwdgxgLglg9mABANwIYBsYBNVQKYAUAzhABZ4C2qAXIkVAE4xgDmAlLQEZxzp6pgA3IgBQoSLAQoM2XIRLkqtek1YdE3XvyQAfRAAUGcCjCJ4APCuYsAfIJFjw0eEjSYc+YmUo06ja+qafAKIeobGphZWrDaIAN4iiEmIDHhQIAxIALK4pAB0DAJYxgRsiLEADHkArIgA-IiMIHiItOEmZgV4RLzIhADkwBhm-Wz2AL4OIhAI9I2IALzS7nIEAETRLGtjQA

Check type of t.

[epoberezkin]

possible problems that keep coming up - 1) disabled strictNullChecks - it should be enabled. 2) typescript version prior to 4.2.3

[epoberezkin]

ah - sorry - it's a different issue

[epoberezkin]

That's a non-trivial trade-off. Majority of users do not use async validation, so for them it would be inconvenient if the return type was guard or promise, it makes it unusable in most cases. That's why it only has Promise in the return type if your schema type is AnySchema or AsyncSchema, which makes it impossible to use for async validation if you want to reference schema via its key/$id... Possibly the solution is to have an additional optional type parameter validate<T, A extends boolean | undefined = undefined> that, if present, would choose a specific return type via conditional type:

A extends undefined ? data is T | Promise<T> : A extends true ? Promise<T> : data is T

[epoberezkin]

The workaround is to use compile instead of validate and to have your schema typed as AsyncSchema

[GabenGar]

Maybe related to this case, but I wrote a validator factory function and stumbled upon the issue of await validate(data) not actually being async. Is $async keyword in the shema the only requirement for the validator functions being async?