Summary

Removes the "virtual struct" (aka struct inheritance) feature, which is currently feature gated.

Motivation

Virtual structs were added experimentally prior to the RFC process as a way of inheriting fields from one struct when defining a new struct.

The feature was introduced and remains behind a feature gate.

The motivations for removing this feature altogether are:

1. The feature is likely to be replaced by a more general mechanism, as part of the need to address hierarchies such as the DOM, ASTs, and so on. See this post for some recent discussion.
2. The implementation is somewhat buggy and incomplete, and the feature is not well-documented.
3. Although it's behind a feature gate, keeping the feature around is still a maintenance burden.

Detailed design

Remove the implementation and feature gate for virtual structs.

Retain the virtual keyword as reserved for possible future use.

Drawbacks

The language will no longer offer any built-in mechanism for avoiding repetition of struct fields. Macros offer a reasonable workaround until a more general mechanism is added.

Unresolved questions

None known.