Policy for Locking Closed Issues

We are automatically locking closed issues - reason being that if an issue re-appears, we'd like to track it as a separate issue (linking to the old, existing issue is encouraged).

The current locking policy can be viewed at https://github.com/icsharpcode/ILSpy/blob/master/.github/workflows/lock.yml

Initially, we added a comment (see sample), however, that created lots of emails potentially a long time after an issue was resolved (to a lot of people). We decided to only lock and set to resolved instead to avoid those emails.