We’re ramping up for the Stack 2 release, which contains a

number of changes. (If you want more information, check out

the changelog.) I’m not going to be covering all of those

changes in this blog post. Instead, today, I want to talk about

what the release process will look like, both for Stack itself and

Stackage.

Stack release process

I’ve created a new Stack 2 milestone on Github to track issues we want resolved before release. I’m also now announcing a 2 week deadline for a feature freeze. If you have a feature you believe belongs in Stack 2,

or a bug fix you’d like to see addressed in this release, now’s the

time to raise it. As usual, pull requests will be more likely to

result in changes happening, and the Stack team is always happy to

help people new to the codebase.

As of 2 weeks from today (May 8), we’ll enter a code freeze period. We’ll cut a release branch and begin releasing

release candidates. New features will not be added to the release

candidate branch, and we will need to weigh carefully which bug

fixes are added to this branch to avoid destabilizing things too

much.

I strongly encourage Stack users to begin experimenting with the

Stack master branch earlier rather than later. You can upgrade to

the latest master by running `stack upgrade --git`.

We will plan for at least a 3 week code freeze period, which may

be extended based on feedback from users. That would make the

earliest release of Stack 2 May 29.

Changes to Stackage

Last year, I wrote a few blog posts

about Pantry. I never really finished that series, and I think some

people were left wondering how this would affect Stack and Stackage

going forward. Let me give a bit more information, now that we know

how Pantry is going to work out. Big thanks to Kirill Zaborsky and

Sibi Prabakaran for all of their work on the Pantry changes.

Pantry is a library for representing Haskell source files in a

fully deterministic way. Each package ends up with a pantry tree

key, which is a hash of its contents, and some description of how

to get the source code. Examples would be from Hackage with a

specific revision, from a Git repository at a certain commit, or

from a tarball.

With Stack 2, we are overhauling the Stackage snapshot file

format to directly use Pantry. This fixes a long-standing

annoyance: we had different snapshot formats for Stackage itself

and for “custom snapshots” in Stack. Those are now unified. It also

addresses a long-standing concern in Stackage: the inability to

patch packages if necessary. By allowing package sources from

outside of Hackage, the Stackage Curator team will now have the

ability to patch packages as necessary.

We’ve already been generating new-style Stackage snapshot files,

which can be viewed at the commercialhaskell/stackage-snapshots

repo. Currently, we’re using the original Stackage build process,

generating the original LTS Haskell and Stackage Nightly snapshot

formats, and converting to the new format. In the next week or two,

we’ll be reversing that: using a new Stackage Curator build tool to

produce snapshot files and perform builds, and then for

compatibility generating the old file formats.

We don’t have a guarantee of how long we will continue to

support the original file format. There are no plans at all to ever

remove the existing files, but at some point in the future we will

stop generating compatibility files. We recommend tooling authors

using the snapshot files directly get in touch to discuss upgrade

paths. (I discussed this offline with some of the Nix contributor

team, but that work was never completed.)

Future: Pantry server

Pantry works via content-addressable storage: each tree and file

can be accessed via its hash. One plan we have for the future is to

write a Pantry server, which will allow Stack (and other tools) to

download package contents via the Pantry key instead of, for

example, needing to clone a Git repository. For compatibility with

tooling already familiar with HTTP(S) and Tarballs, we’ll likely

provide such an interface to this store as well.

That said: we are not including this feature in Stack 2.

It is slated for a later release. Personally, I think it will be a

fun project. If anyone’s interested in working on this, feel free

to comment on the issue.

Further details about Pantry

I’m not sure if Pantry is a topic people are interested in

hearing more about and using it in their own projects. For now, I’m

keeping the details relatively high-level in this post. If there's

a demand for more information, hit me up with questions and I can

put together another post answering them.