mudasobwa

mudasobwa

Creator of Cure

As a library author, I am aware of my users having a good no-warning experience, and the current implementation of how warnings regarding gradual type checks are reported now drives me bonkers.

In my library Tempus I have several guards allowing date(-time) comparison with calendars in mind. Let alone different calendars (which work to some extent,) it’s optimized for cases when both calendars are Calendar.ISO.

To calculate the difference between two datetimes in a guard, I need to deal with leap years/seconds, and the only way to do so in a guard is to lookup the compile-time map for the elapsed amount of days.

The newly introduced type warnings blow in the face of my users with

[…]
:erlang.map_get(:erlang.map_get(:month, :erlang.map_get(:to, s2)), %{
             1 => 0,
             2 => 31,
             3 => 59,
             4 => 90,
             5 => 120,
             6 => 151,
             7 => 181,
             8 => 212,
             9 => 243,
             10 => 273,
             11 => 304,
             12 => 334
           }) * 86400

Conflict found at
  lib/guards.ex:637: Tempus.Guards.joint_in_delta?/3

warning: expected Kernel.*/2 to have signature:

    dynamic(), true | false | float() | integer() -> integer() | float()

but it has signature:

    integer(), integer() -> integer()
    float(), integer() | float() -> float()
    integer() | float(), float() -> float()

The values of this map are integers, the map itself is a compile-time beast, but the warning still exists.


So instead of providing a pull request to fix this case when the type might be easily derived from the set of map values, I wonder if library creators can explicitly tell the type checker, hey, I know what’s going there, please, don’t overreact.

Thanks!

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