Generating fully resolved snapshots

[Alexander Bondarenko]

Hi!

Stack 2.1.3 had "freeze --snapshot" command that put all "completed" parts together with originals. The result then could be fed to "--resolver" option removing the need to download stuff or update pantry db.

This allows a read-only stack root which then can be shipped as a deb package.

With 2.3 removing the command one has to mess around lock files to assemble the said snapshot. Are there any alternatives? Maybe bring back snapshot generation as a standalone command?

[Michael Snoyman]

Thanks for raising this before the release :)

The functionality for adding complete package information to a snapshot file lives in the pantry package, not in Stack. I think I'd like to go in the direction of exposing this functionality via Pantry instead of Stack, since I don't want to add the complexity back into Stack. Also, the original reason for removing the freeze functionality was due to questions of how to handle now-deprecated hpack-only packages. I'd rather not get into that debate again, and leave that handling up to the caller.

I've put together a Gist demonstrating how to complete a snapshot layer:

https://gist.github.com/snoyberg/99849b2c92b1a34f0cd9c509e2161ab7

It includes a `foo.yaml` custom snapshot file, and a `Main.hs` which uses that snapshot for running, and then generates a `bar.yaml` with the package and snapshot information completed. I could imagine adding an executable-maybe optional-to the pantry package to expose this functionality. What do you think?

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[Alexander Bondarenko]

Thanks! This would be most helpful.

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[IC Rainbow]

Now, having integrated snapshot resolver into my build I think making
it a standalone executable would be much better.
Pantry brings quite a few dependencies and grafting it unto Shake
build looks suboptimal.
And I worry about stack/pantry being buildable with latest and
greatest stackage snapshots. Tracking nightlies isn't a priority for
stack, but sometimes a need of our own.

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[Michael Snoyman]

I'm not sure what you're saying your desired outcome is here. Are you planning on using the Haskell file I provided and compiling it yourself?

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[IC Rainbow]

I'm still in a PoC phase for now, but yep, I put a variation of your
snippet in my tool. It required tuning my extra-deps for LTS-13 build.