Generate consistent validation error messages in `RetryPolicy`

[snicoll]

Looking at RetryPolicy.builder() for invalid cases, the exception message for maxDelay is not consistent.

If the delay is negative, the error message is Invalid delay (-1ms): must be >= 0.. If the maxDelay is negative, it is Invalid duration (-1ms): maxDelay must be positive..

There is an assertIsPositive() method that's only called by maxDelay().

[sbrannen]

If the delay is negative, the error message is Invalid delay (-1ms): must be >= 0.. If the maxDelay is negative, it is Invalid duration (-1ms): maxDelay must be positive..

According to the current documented contracts, those exception messages are correct.

delay is currently required to be non-negative (>= 0).

maxDelay is currently required to be positive (> 0).

Originally, they were both required to be positive, but I changed that in cc31bf3 to align with the semantics for @Retryable.

Conceptually, I don't think it makes much sense for maxDelay to be zero. If a user does not want a delay, setting delay to zero should suffice.

However, for consistency with the changes made in cc31bf3, I'll modify RetryPolicy.Builder to allow zero for maxDelay as well, and I'll repurpose this issue to address that.

There is an assertIsPositive() method that's only called by maxDelay().

Historically, that was used in multiple methods since Duration does not provide an isPositive() method. However, when I make the aforementioned changes I'll likely convert that to a reusable assertNonNegative() utility.

[snicoll]

According to the current documented contracts, those exception messages are correct.

I am not denying that, and that's not what I am reporting. Please triage the issue as described rather than repurposing it for something I didn't ask.

One error message is: "Invalid delay (-1ms): must be >= 0."
The other is: "Invalid duration (-1ms): maxDelay must be positive."

I would expect something like "Invalid maxDelay (-1ms): must be > 0." or the other way around if the team feels like the second error message is more explicit.

[sbrannen]

Thanks for the feedback, @snicoll. 👍

And I apologize for misinterpreting the intent of this issue.

I have changed the title to reflect the current scope: consistent error messages for all validation in RetryPolicy.