Plan for enum discrim, repr, and casting

[pnkfelix]

Summary

We have long-standing open issues regarding how/whether one can cast an enum to its discriminant value.

We have found when touching on this topic in the triage meetings that we need a dedicated design meeting to better understand the status quo, where we might go next, and where we want to go.

@jswrenn will work with @pnkfelix on making a document to drive the meeting.

Background reading

rust-lang/rust#88203

rust-lang/rust#60553 (comment)

About this issue

This issue corresponds to a lang-team design meeting proposal. It corresponds
to a possible topic of discussion that may be scheduled for deeper discussion
during one of our design meetings.

[fleith]

Is there any schedule for this? Looking forward to see this feature! :)

[nikomatsakis]

Re-open if still relevant