Support +inf/-inf for the PgNumeric type

[cmpute]

Positive and negative infinities are introduced in Postgres 14. Currently the PgNumeric type only supports normal floats and nan.

[cmpute]

It's likely going to be a breaking change but it still should be implemented. In case the client is connecting to the server with an older version, a runtime error should be returned for infinities.

[weiznich]

Thanks for filling this feature request. I agree that we should somehow support this and I'm open to hear suggestions how to implement this. As a important note: We likely wont accept a breaking change for to accept this feature anytime soon as we don't plan to issue another major diesel version anytime soon (== next years).

[cmpute]

For a short term fix without break changes, I think it will suffice to create a wrapper like this:

enum PgNumericWithInf {
    PosInfinity,
    NegInfinity,
    Others(PgNumeric)
}

and then implement FromSql and ToSql for this type as well.

[weiznich]

I would accept a PR for this as long as it contains documentation + tests