reno/doc/source/user/design.rst

Design Constraints and Requirements

Managing release notes for a complex project over a long period of time with many releases can be time consuming and error prone. Reno helps automate the hard parts by devising a way to store the notes inside the git repository where they can be tagged as part of the release.

We had several design inputs:

• Release notes should be part of the git history, so as fixes in master are back-ported to older branches the notes can go with the code change.
• Release notes may need to change over time, as typos are found, logical errors or confusing language needs to be fixed, or as more information becomes available (CVE numbers, etc.).
• Release notes should be peer-reviewed, as with other documentation and code changes.
• Notes are mutable in that a clone today vs a clone tomorrow might have different release notes about the same change.
• Notes are immutable in that for a given git hash/tag the release notes will be the same. Tagging a commit will change the version description but that is all.
• We want to avoid merge issues when shepherding in a lot of release-note-worthy changes, which we expect to happen on stable branches always, and at release times on master branches.
• We want writing a release note to be straight-forward.
• We do not want release notes to be custom ordered within a release, but we do want the ordering to be predictable and consistent.
• We must be able to entirely remove a release note.
• We must not make things progressively slow down to a crawl over years of usage.
• Release note authors shouldn't need to know any special values for naming their notes files (i.e., no change id or SHA value that has special meaning).
• It would be nice if it was somewhat easy to identify the file containing a release note on a particular topic.
• Release notes should be grouped by type in the output document.
  1. New features
  2. Known issues
  3. Upgrade notes
  4. Security fixes
  5. Bugs fixes
  6. Other

We want to eventually provide the ability to create a release notes file for a given release and add it to the source distribution for the project. As a first step, we are going to settle for publishing release notes in the documentation for a project.

Assumptions

Based on the above, reno makes a couple of assumptions about the release policy used for a given project. reno expects all development, including bug fixes, to take place on a single branch, master. If stable or release branches are used to support an older release then development should not take place on these branches. Instead, bug fixes should be backported or cherry-picked from master to the given stable branch. This is commonly referred to as a trunk-based development workflow.

* bc823f0 (HEAD -> master) Fix a bug
|
| * 9723350 (tag: 1.0.1, stable/1.0) Fix a bug
| * 49e2158 (tag: 1.0.0) Release 1.0
* | ad13f52 Fix a bug on master
* | 81b6b41 doc: Handle multiple branches in release notes
|/
* 0faba45 Integrate reno
* a7beb14 (tag: 0.1.0) Add documentation
* e23b0c8 Add gitignore
* ff980c7 Initial commit

(where 9723350 is the backported version of bc823f0).

By comparison, reno does not currently support projects where development is spread across multiple active branches. In these situations, bug fixes are developed on the offending stable or release branch and this branch is later merged back into master. This is commonly referred to as a git-flow-based development workflow.

* 7df1078 (HEAD -> master) Merge branch 'stable/1.0'
|\
| * 9723350 (tag: 1.0.1, stable/1.0) Fix a bug on stable
| * 49e2158 (tag: 1.0.0) Release 1.0
* | ad13f52 Fix a bug on master
* | 81b6b41 doc: Handle multiple branches in release notes
|/
* 0faba45 Integrate reno
* a7beb14 (tag: 0.1.0) Add documentation
* e23b0c8 Add gitignore
* ff980c7 Initial commit

When this happens, reno has no way to distinguish between changes that apply to the given stable branch and those that apply to master. This is because reno is branch-based, rather than release-based. If your project uses this workflow, reno might not be for you.

More information is available here.