Return a static string for Enum::variant_name

[cBournhonesque]

Objective

The reflect::Enum::variant_name() should return a static string; the name returned shouldn't depend on the lifetime of the enum itself. I'm using reflection with Enums in a library and I was expecting the variant_name function to give me a string that is indenpendent to my object's lifetime

Caveats:

• are there some cases where we wouldn't want to return a &'static str?
• we should probably have the same thing for reflect::Enum::name_at() but I wasn't able to get it working because of DynamicEnum

Migration Guide

• reflect::DynamicEnum now requires a &'static str for the variant_name instead of a String

[MrGVSV]

One concern is: how would a user generate these dynamically?

For example, they might have their own custom deserialization logic which returns a String. Or maybe they're parsing a script that contains non-Rust enum types.

They could intern their strings, but I'm not sure we want to require that until we have a better idea of how we might want to handle these dynamic cases. And I have a feeling we won't be able to do that until we see Unique Reflect in action.

[cBournhonesque]

One approach would be to leak the memory of the string? Set_variant shouldn't be called very often.

I guess it's problematic to return &'static str for variant_names in the DynamicEnum case..

[alice-i-cecile]

Yeah, I'm similarly worried about how this interacts with dynamic enums. Unless we can prove that this is fine, I don't think we should merge this.

[cBournhonesque]

Will close for now since there's issues related to DynamicEnum