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Versioning and release processes

Versioning Process

Ledger team has fully adopted the PVP versioning scheme for all packages in this repo.

Updating the version for every package in this repository is the responsibility of the developer that is introducing a change to any package that is subject to release process. Version must be updated in both the CHANGELOG.md and in the .cabal file for the package in the same PR, as well as every other package that is affected by the change in the repository. Every affected package that is subject to release process must receive a lower and, potentially, an upper bound update on the dependency that has experienced the change.

For example if I add a function to cardano-ledger-core and use it in cardano-ledger-conway, then I must add a minor version bump to cardano-ledger-core and I also must add a lower version restriction in cardano-ledger-conway for cardano-ledger-core, as per PVP.

In other words, when it comes to versioning, the fact that all of the packages in this repository are built together at the same time should be ignored. It should be assumed that every package and all of its required dependencies can be released to CHaPs at any point in time. This is necessary to guarantee that if such a package is compatible with other packages from this repository, which have been previously released, the version bounds should reflect that.

Upper bounds

Normally, upper bounds are required by PVP for all dependencies of a package. This is the only exception we make to the PVP, and we do not require strict upper bounds for dependencies that come from Hackage. For example, there is no need to add an upper bound on containers package, unless there is a known incompatibility. Speculative upper bounds over time lead to overly restrictive build plans that are forced to favor older packages. Moreover, they lead to a lot of redundant maintenance burden. That being said, most of the packages from within cardano-ledger repository are a lot more volatile and require tight interoperability, therefore speculative upper bounds are encouraged.

Lower bounds

Placing lower bounds is a lot less controversial than upper bounds, because they don't suffer from speculation about the future. Older versions of dependencies are known at release time. Therefore lower bounds must be added for all dependencies that are known to be incompatible with the package

Handbook

See the versioning section of the Cardano Engineering Handbook for more detailed information on this topic.

CHANGELOG.md

Every package, that is subject to the release process, will always have the top most entry in the CHANGELOG.md set to an unreleased version. That top most section will have either the patch, minor or the major versions bumped, but not all three, when compared to the latest released version. Which one it will be depends on the recent changes that were added after the latest release was made. More on why this should always be true is in the Release Process section. For instance, if the latest version of cardano-ledger-core that was released to CHaPs is 1.2.3.0, then there will be a section like this which will have a version that is strictly higher than 1.2.3.0, eg:

# Version history for `cardano-ledger-core`

## 1.2.3.1

* Add ...
...

In order to decide if the version needs to be bumped up it is necessary to know what was the latest released version of a package. Two simple ways are either look at the version on CHaP or look at the latest git tag for the version.

However the easiest, while also reliable way to figure out whether you need to bump up the version is to simply look at the current version in the changelog. It will be easier to explain why this is the case with an example.

Let's say you submit a PR which contains breaking changes to cardano-ledger-core. You then look into the changelog for current development version on master:

  • If the current version is set to cardano-ledger-core-1.2.3.5. We see that the patch version is bumped (not zero), that means that the latest version released is cardano-ledger-core-1.2.3.4, so you update it to cardano-ledger-core-1.3.0.0, because your changes break stuff
  • If the current version is set to cardano-ledger-core-1.2.4.0. That means there was at most a minor version bump and currently released version is cardano-ledger-core-1.2.3.x. But your changes are breaking so you increase it even further to cardano-ledger-core-1.3.0.0
  • If the current version is cardano-ledger-core-1.3.0.0. That means currently released version to CHaPs is cardano-ledger-core-1.2.x.x. There is nothing to do, the version on master already contains some other breaking changes since the last release to CHaPs
  • If the current version is cardano-ledger-core-2.0.0.0. There was a complete overhaul. Definitely nothing needs to be bumped. 😁

It is quite common to experience conflicts in the changelog, since that will be the most common section of the codebase being updated at the same time. When it comes to conflicts resolution, it is pretty easy:

  • on the package version, the highest value should usually win.
  • on the change log entries, all entries should usually survive.

New entries should always be prepended to the top of the section.

When to update

CHANGELOG.md must be updated for the package that is experiencing a change and any other package in the repository that re-exports that change in one form or another. In general an entry is added according to these rules:

  • Every breaking change MUST appear in the CHANGELOG.md.

  • Every non-breaking change SHOULD appear in the CHANGELOG.md

  • Every change that does not affect the user facing semantics of the code (eg. changes to documentation, dependency bounds, test suites, addition of internal functions, performance improvements, etc.) COULD be added to the CHANGELOG.md, but they are discouraged. Exceptions should be made for changes that could really be valuable to the downstream user.

  • Every change to a public sub-library of a package must be added to a separate section in the CHANGELOG.md and is versioned together with the main library. Eg. testlib:

    # Version history for `cardano-ledger-core`

## 1.20.2.0

* Add `someFunction`

### `testlib`

* Add `Arbitrary` instance for ...
...

Release Process

Usually a package release will happen directly from the master branch. Current release process even allows for a release to happen from a commit that is slightly behind HEAD of the master branch. On a rare occasion when a bugfix needs to be backported to an older version, a release can happen from an ephemeral release branch. Such a release branch must follow the same procedure of a PR review and CI, that is why it should be prefixed with release/some-branch-name, because that will ensure that CI is triggered.

Release Steps

Here are the steps for a release engineer to follow.

Decide what to release

Normally it should be OK to release at the same time all of the packages from the repository that have experienced some sort of change, but that is not mandatory. It is fine to release any package by itself at any point from the HEAD of master or even a commit that is behind the HEAD on the master branch. A release from an ephemeral branch is also possible, but it is paramount to ensure that all of the same changes will be present in the next release from master branch.

The most common case is to blindly release all of the packages that were changed since they were last released. This begs a question. How to decide which of the packages have changed, thus deserve a release?

The rule is very simple. Every package that falls under this release process and has a version in its cabal file higher than the highest version released to CHaPs is allowed to be released. It is also possible to rely on git tags for deriving information about the latest released version of a package, because it is a mandatory step after the release to CHaP. (TODO: implement a script that lists all of the package that fit the above criteria)

Release to CHaP

  1. Follow the CHaP release instructions

    For example, to release commit with SHA deadbeef:

    $ ./scripts/add-from-github.sh https://github.com/intersectmbo/cardano-ledger deadbeef libs/cardano-ledger-core ...

    It is important to supply a commit SHA instead of a branch name.

  2. Create and merge a PR to https://github.com/intersectmbo/cardano-haskell-packages with the release(s). In case that a current release causes breakage on some downstream package due to that package lacking upper bounds, you will require to add a revision for that package that fixes the bounds in the same PR as the release. Also it is necessary to notify the maintainers of the package via a bug report or a PR with a fix.

  3. Once the PR is merged then create a git tag with the same version for the same git SHA that was released, eg:

    $ git tag cardano-ledger-core-1.20.1.1 deadbeef...
$ git push tag cardano-ledger-core-1.20.1.1

  4. Create a PR to master that updates CHANGELOG.md files for all of the packages that have just been released. The only addition to the file should be a markdown header section with the next patch version bumped, which must bring the CHANGELOG.md to the state of the top level section containing a version higher than the highest one ever released. Due to concurrent nature of editing the repository it is possible that CHANGELOG.md have already received a version bump with a section that fits the higher version criteria, in which case nothing needs to be added. The body of the section, if added, must be empty with just one single asterisk *.

    For example, if cardano-ledger-core-1.20.1.1 was just released, then a new empty 1.20.1.2 section in the CHANGELOG.md must be added:

    # Version history for `cardano-ledger-core`

## 1.20.1.2

*

## 1.20.1.1

...

    It is important to note that the version in the cabal file should not be changed at this stage, because it will later be used for deciding which package have changed and can be released.

Adding revisions

As mentioned above, sometimes a release could break downstream packages in which case you will need to add revisions. The instructions here will walk you through a specific case that we had when we released some packages in cardano-base and will also provide general instructions on how to add and test revisions.

Backporting changes

It is occasionally necessary to release a minor version for a package that has its history diverged from a version on master significantly enough to make it impossible for a minor version to be released from master. In other words a patch backporting. In such a scenario a few steps should be followed:

  1. Two ephemeral branches with a prefix release/ need to be created. Both should branch of from a tag of a package version that is being updated. For example if a current version on master is cardano-ledger-core-1.22.10.0 then the latest cardano-ledger-core-1.21.x should be used as base:

    $ git checkout -b release/cardano-ledger-core-1.21.2.1 cardano-ledger-core-1.21.2.1
$ git push -u origin release/cardano-ledger-core-1.21.2.1
$ git checkout -b release/cardano-ledger-core-1.21.3.0 cardano-ledger-core-1.21.2.1

    We'll need the first branch in order to use it as base when creating a PR for code review.

  2. Changes that need to be released should be cherry-picked from master. If a fix on master was implemented in some incompatible fashion to the current release, then it is fine to reimplement it anew, as long as the change being introduced is also present on master in some form. That requirement also concerns the changelog entry, it should be present in both the patched version and in the next version released from master.

  3. Regular release process should follow from here.

  4. Once the package has been released and a git tag for that release was created, both of the release/ branches can be removed.

This process does not accommodate backporting fixes to versions that are at least two major versions behind the one on master.

Packages excluded from release process

We release most of the packages in this repo to CHaP (Cardano Haskell Packages). However, there are a few packages that are either used for testing, debugging or benchmarking and do not deserve to be released into the World. They are neither released nor versioned. Bounds on the local dependencies do not need to be updated, because they will always use the versions for ledger packages from within the repository, rather than from CHaPs. Here is the full list of such packages as of today:

  • libs/cardano-ledger-test
  • libs/plutus-preprocessor
  • libs/ledger-state

Above list is likely to change in the future.

Test packages

Here are test suite packages that are still subject to the versioning and release process, but the changelog only needs to indicate if breaking changes have been made:

  • cardano-ledger-shelley-test
  • cardano-ledger-shelley-ma-test
  • cardano-ledger-alonzo-test
  • cardano-ledger-babbage-test
  • cardano-ledger-conway-test
  • cardano-crypto-test
  • cardano-ledger-byron-test

A changelog which indicates that no changes have been made will have the form:

# Version history for `cardano-ledger-conway-test`

## 1.2.0.1

*

A changelog which indicates that changes have been made will have the form:

# Version history for `cardano-ledger-conway-test`

## 1.3.0.0

* breaking changes

These packages are mostly used internally and are planned to be deprecated and removed in the near future in favor of testlibs for each corresponding package.