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Branching_Model.md

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Branching Model

Semantic Versioning

Details: http://semver.org/, http://apr.apache.org/versioning.html

Versions are denoted using a standard triplet of integers: MAJOR.MINOR.PATCH. The basic intent is that MAJOR versions are incompatible, large-scale upgrades of the API. MINOR versions retain source and binary compatibility with older minor versions, and changes in the PATCH level are perfectly compatible, forwards and backwards.

Patch level changes could also be for correcting incorrect APIs. In this case, the previous patch release may be incompatible, but because of bugs.

Minor versions may introduce new features, but do not alter any of the previous API.

Major versions may introduce new features and change the old API in incompatible ways.

Git workflow

The different types of branches we may use are:

  • main

    • production releases

  • develop

    • AKA integration branch

  • Release branches (release-*)

    • for finalizing a major/minor release, branched from develop

  • Hotfix branches (hotfix-*)

    • for applying patches, branched from main (or support-* for older releases)

  • Support branches (support-*)

    • for applying patches to old release versions, branched from main

  • Feature branches (feature-*)

    • for developing features or wild speculation, branched from develop

chart

Feature branches

Created for feature development that may require several or more commits to produce a working tree. May make occasional merges from develop to keep it up to date. If it will be separate for an extended period of time, create a feature-branch-readme.txt in the top level directory dictating the reason for the branch.

May branch off from: develop

$ git checkout -b myfeature develop

Must merge back into: develop

$ git checkout develop
$ git merge --no-ff myfeature
$ git branch -d myfeature
$ git push origin develop

feature

Release branches

Release branches are created when the develop branch is at a stable point and release specific changes need to be made, such as bumping version numbers, etc. At that point, develop should be branched and the changes made before ultimately merging it into main and tagging the release. There should only be one active release branch at a time. Until the current release is wrapped up, merged into main and deleted, development of the next release should take place on develop. When develop reaches another state of stability for release, another release branch is be created.

May branch off from: develop

$ git checkout -b release-1.2 develop
$ ./bump-version.sh 1.2
$ git commit -a -m "Bumped version number to 1.2"

Bug fixes made on a release branch may be merged back into develop continuously if needed, though ultimately they will be merged in when the release is finalized.

Must merge back into: develop and main

$ git checkout main
$ git merge --no-ff release-1.2
$ git tag 1.2

$ git checkout develop
$ git merge --no-ff release-1.2

At this point the release branch is safe to delete, since the changes are reflected in develop and main. If the branch is remote, remove the remote branch also. $ git branch -d release-1.2

Hotfix branches

Patches that need to be made to the most recent production release are applied to a hotfix branch off main. For older releases, hotfixes branch off a support-* branch (explained later.)

May branch off from: main

$ git checkout -b hotfix-1.2.1 main
$ ./bump-version.sh 1.2.1
$ git commit -a -m "Bumped version number to 1.2.1"

$ git commit -m "Fixed severe production problem"

Must merge back into: develop and main

$ git checkout main
$ git merge --no-ff hotfix-1.2.1
$ git tag 1.2.1

Merge into develop only if there is no current release branch, otherwise, merge into release branch instead.

$ git checkout develop
$ git merge --no-ff hotfix-1.2.1

Finally, delete. $ git branch -d hotfix-1.2.1

hotfix

Support branches

If main has moved on a point release (1.0, 1.1, 2.0, etc) and a hotfix must be applied to a older version ( e.g 1.x):

  • create a support-1.x branch (if none exists) based on the newest 1.x tag in main
  • create a branch (e.g. hotfix-1.1.1), based on support-1.x
  • fix the bug and merge hotfix-1.1.1 back into support-1.x
  • Do this for other older major releases as necessary

The support branch effectively becomes a main branch for a past version.