Summary

Go over the state of the various idiom lints that may be part of the 2021 Edition and make decisions about the course of action we expect.

Preparation

@scottmcm to prepare, for each idiom lint:

• summarize current state (warn by default? etc)
• summarize concerns that have been raised
• proposed action in 2021 Edition
  • (default: Deny by default)
• does the warning have automatic migrations
• crater results, if applicable

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.