Respect precision for intervals

[greg-rychlewski]

In the previous PR we hardcoded the precision to 6 because we didn't know how to deal with the type modifier.

I got pointed in the right direction by the nice people at Postgres. The type modifier for intervals takes into account two different things:

1. The allowed fields (i.e. only days, years, days to years and stuff like that), represented as a 16-bit bit field
2. The precision represented as a 16 bit integer

The right most 16 bits in the type modifier are the precision. I was pointed to the right places in their code here and here

We could probably do something about the fields modifier as well but that is a lot more complex. And we ignore it already today. So going to think on it a bit and save it for later.

[greg-rychlewski]

Sorry I'm not sure how to get rid of this warning when using lower Elixir versions =(

Check warning on line 9 in lib/postgrex/extensions/interval.ex

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/ test (9.4, skip_wal, 1.11.4, 23.3.3)

unused import Bitwise

[wojtekmach]

import Bitwise, warn: false

[greg-rychlewski]

Just to be extra cautious:

Is it safe to assume across elixir/erlang versions that -1 &&& 0xFFFF is always 0xFFFF

[josevalim]

Yes. Otherwise it would have to be a breaking change in Erlang.