Add checklist template to release documentation

docs/docs/contributing/release.md

@@ -33,6 +33,43 @@ CI is set to automatically detect the tags of the format discussed above and per
 The CI operation is entirely automatic provided you have tagged the release correctly. No need to do anything here.
 
 ## Documentation
+### Release Procedure Checklist
+Before we start the release procedure, we create an issue with a release checklist. As we go through the release, we update the checklist. In the checklist template below, the following variables are used:
+
+- `<stable-version>` is the stable version being released, e.g. `0.14.0`. It is identical to the git tag under which it is released.
+- `<rc-version>` is the version of the RC version being released, e.g. `0.15.0-RC1`. It is identical to the git tag under which it is released.
+- `<stable-branch>` is the name of the stable branch being released, e.g. `0.14.x` if we are releasing `0.14.0`
+- `<rc-branch>` is the RC's branch. E.g. if we are releasing `0.14.0` and `0.15.0-RC1`, the RC version is `0.15.0-RC1`, and `<rc-branch>` is `0.15.x`.
+- `<next-version>` is the tech preview version. It is the next version after the currently released RC. E.g. if we are releasing `0.15.0-RC1`, this variable will be `0.16.0`.
+
+A good workflow is to compute these variables before each release, then replace them in the checklist below:
+
+```
+- [ ] Publish artifacts to Maven via CI
+  - [ ] On branch`<stable-branch>`, set `baseVersion` to `<stable-version>` and `git tag` it as `<stable-version>`. This will publish artefacts to Sonatype and GitHub Release
+  - [ ] Merge branch `<stable-branch>` into `master` to guarantee that all of the `<stable-branch>` commits are propagated to `master`
+  - [ ] Look at the milestone of the RC version being released. Move all the open issues from it to the next milestone.
+  - [ ] Create branch `<rc-branch>` from `master`
+  - [ ] On `<rc-branch>`, set `baseVersion` to `<rc-version>` and `git tag` it as `<rc-version>`. This will publish artefacts to Sonatype and GitHub Release.
+  - [ ] On `master`, set `baseVersion` to `<next-version>`
+- [ ] Update `scalaVersion` (and, if applicable, the `sbt-dotty` version) in the Dotty ecosystem projects
+  - [ ] https://github.com/lampepfl/dotty-example-project 
+  - [ ] https://github.com/lampepfl/dotty-example-project/tree/mill
+  - [ ] https://github.com/lampepfl/dotty.g8
+  - [ ] https://github.com/lampepfl/dotty-cross.g8
+  - [ ] https://github.com/lampepfl/homebrew-brew
+  - [ ] https://github.com/lampepfl/packtest
+  - [ ] https://github.com/scalacenter/scastie
+  - [ ] Dotty itself – update the `referenceVersion` in the `master` branch to `<rc-version>`. This is the version of Dotty used to compile the Dotty codebase on `master`.
+  - [ ] Scalac CI, like this: scala/scala#7993
+- [ ] Announce the release
+  - [ ] Publish releases for the RC and stable versions on GitHub Releases
+  - [ ] Publish Blog Post on dotty.epfl.ch
+  - [ ] Make an announcement thread on https://contributors.scala-lang.org
+  - [ ] Tweet the announcement blog post on https://twitter.com/scala_lang
+```
+
+### GitHub Releases and Blog Post
 After the release is done, we document it as follows:
 
 - On the GitHub release page, modify the release drafts created by CI. The RC draft should include notable changes introduced since the previous RC. E.g. for `0.14.0-RC1` these are generated by `gren changelog -G --override -D prs --tags=0.13.0-RC1..0.14.0-RC1`. `gren` is available [here](https://github.com/github-tools/github-release-notes), and before running the above command, please make sure that (1) the `origin` branch points to the `lampepfl/dotty` repository and (2) the two tags mentioned in the command are pushed to the `master` branch of that repo. Otherwise, the command won't pick up the tags.
@@ -42,7 +79,7 @@ After the release is done, we document it as follows:
 After releasing a new version of Dotty, we need to make sure to update the following related projects:
 
 - [Example Project](https://github.com/lampepfl/dotty-example-project)
-- 🚫[Example Project with Mill](https://github.com/lampepfl/dotty-example-project/tree/mill) – FTTB doesn't work with new Dotty releases, see lampepfl/dotty-example-project#26
+- [Example Project with Mill](https://github.com/lampepfl/dotty-example-project/tree/mill)
 - [Dotty G8 template](https://github.com/lampepfl/dotty.g8)
 - [Dotty G8 template with cross build support](https://github.com/lampepfl/dotty-cross.g8)
 - [Dotty Homebrew Formula](https://github.com/lampepfl/homebrew-brew)