[Feature]: Roll back to previous packages version

[jumper047]

Feature Description

As far as I know, Straight.el has command straight-freeze-version. Is similar feature planned for Elpaca? Ideally, I would love to have ability to roll back packages versions to ones before last upgrade

Confirmation

• The feature I'm proposing does not already exist in Elpaca

[progfolio]

Is similar feature planned for Elpaca?

Yes. The elpaca-write-lockfile and elpaca-load-lockfile commands are stubbed out in elpaca.el.
I'm still considering some aspects of the design.

I would love to have ability to roll back packages versions to ones before last upgrade

My plan is to make general commands that would make this easy to do.
I don't know if I'll provide a "roll back to the the versions just before an update" command specifically, but it will be easy to write one.

[noctuid]

It would be nice if these things would be supported:

• A command to write the current hash for a single package
• A key to manually ignore a dirty work tree when processing packages and just write the hash
• A setting to automatically ignore a dirty worktree for certain packages (my main reason for wanting this is that the first Emacs packages I wrote have a lot of unused files I need to clean up but haven't had the time to; I also have todo files in some repos I'd like to clean and add at some point rather than .gitignore)
• An option to to print using lv or something else (so messages/prompts persist even if something else prints to the echo area)
• Some command to validate a configuration/lockfile. Sometimes a recipe (normally a custom one) is no longer valid due to the repo moving, for example. I've even seen a couple cases where a hash was no longer valid due to force pushes to master... It may be overkill/unreasonable for elpaca to do this. You can validate manually by running Emacs with a different home directory, for example.

[progfolio]

Rudimentary support for lock files added.

• A command to write the current hash for a single package

Should be possible via elpaca-lock-file-functions.

• A key to manually ignore a dirty work tree when processing packages and just
  write the hash

Currently no worktrees are checked. Current hash is written.

• Some command to validate a configuration/lockfile. Sometimes a recipe
  (normally a custom one) is no longer valid due to the repo moving, for
  example. I've even seen a couple cases where a hash was no longer valid due to
  force pushes to master... It may be overkill/unreasonable for elpaca to do
  this. You can validate manually by running Emacs with a different home
  directory, for example.

I think attempting a bootstrap with the --init-directory option or using the elpaca-test macro should work for this.

[progfolio]

I would love to have ability to roll back packages versions to ones before last upgrade

On latest master you should be able to:

1. M-x elpaca-write-lock-file to the desired path.
2. Update desired packages.
3. M-x elpaca-delete any packages you want to roll back.
4. (setq elpaca-lock-file "/path/to/file/from/step/one.eld")
5. M-x restart-emacs

At that point the packages should be installed in the state they were in at step 1.
This workflow could be automated to some extent by interested parties.
I have plans to do more work on lock files in the future, but it's enough to get started with.