package:linter nnbd migration plan

[pq]

The package:linter migration plan:

• 1. land an initial migration that is as tool-driven as possible that runs tests, etc in unsound mode (@pq)
• 2. follow-up with changes to tidy up lib (e.g., remove unnecessary null operators) (@pq) (see: nnbd migration linter#2452 (review))
• 3. cleanup tool (gated somewhat by dev_dependencies such as github) (@pq)
• 4. fix-up build scripts and remove unsound flags (soundness fixes linter#2467)

1. and 2. will happen before a release (3 is stretch).

Related issues:

SpinlockLabs/github.dart#236

In conversation, @bwilkerson and I agreed (again) how nice it would be to have some lints to disallow ?s and !s as this would help in tidying. (I think @scheglov is wanting something similar.)

[bwilkerson]

To be clear, I don't think we want a lint to disallow ?s. There are times when they're necessary. I just want one to disallow null checks because I think they're almost always wrong.

[scheglov]

I thought so too, that Type? and ?. are useful and are not unsafe.
But ! null checks are unsafe.

[pq]

Sorry yes, I wrote in haste. I 100% agree.