bug#41604: guix pull impossible after rebasing a local repository

[zimoun <zimon.toutoune@gmail.com>]

Hi John,

On Sat, 30 May 2020 at 04:26, John Soo <jsoo1@asu.edu> wrote:

> Yeah guix pull --commit=1444040933 --allow-downgrades failed.

Hum?  with this message:

--8<---------------cut here---------------start------------->8---
guix pull: error: Git error: object not found - no match for id
(57518fc7bf1efc899c0dabaa76685a319661f8e4)
--8<---------------cut here---------------end--------------->8---

?


> > Hehe! Dangerous zone. :-)
>
> I think I found that out, haha!

To be honest, I have tried to use the checkout
~/.cache/guix/checkout/pjmkglp4t7znuugeurpurzikxq3tnlaywmisyr27shj7apsnalwq
 as local clone in order to rebase, worktree and apply patches.  Bad,
really bad idea!  The discipline to avoid breakage is too high. ;-)


> I guess that makes me wonder what the desired specification is.
> There is a lot of problem space to explore.  As a user I would want to
> be able to take my local patches as "the real truth".
>
> Because guix has a linear git history, that means the user needs to
> always rebase.  Often I have patches open for months that I am currently
> testing and working on. It would be convenient for me to be able to guix
> pull into my default user profile.
>
> On the other hand, as you point out, using a hash that disappears from
> the git history is dangerous. The git history no longer tracks the guix
> pull history and then there may exist pulls in history that may never be
> recoverable.
>
> There seems to be some existing support for the rebasing into the
> default profile since branches are allowed as references in the channels
> configuration. Has the rebase use case been discussed before? Oh, also,
> history items can be deleted in other places with --delete-generations
> and friends.  I am not sure what to classify this problem, bug or
> something else.

I am not sure to see what is the desired specification.  Well, I do
not know if my workflow is the good one but let me describe how it is
organised.

The local (master) checkout is at ~/src/guix/guix/ and then I only
checkout the branches using 'worktree' (thanks to Ricardo to show me
the tips during a "Skill Share" session on Dec. 2018 :-)).  Well,
Magit helps a lot here.
Basically all my branches live under ~/src/guix/wk/.  And when I test
patches, I always create a new branch.  Well, I do not often rebase
enough so I never remember the 'onto' direction so I always read the
doc for that. :-)

(The price to pay with worktree is that I "compile" all Guix really
often because it does not reuse .go files; even if I tried to
synchronize the .go files to avoid such annoyance but I have failed.)

Just 'guix' refers to the one living at ~/.config/guix/current because
I always want that "guix install foo" refers to upstream.  Well, I
never pull the latest commit from
https://git.savannah.gnu.org/git/guix.git because the substitutes are
almost never available so I pull 2 weeks behind.  Basically, I do:
"git -C ~/.cache/guix/pjmkglp4t7znuugeurpurzikxq3tnlaywmisyr27shj7apsnalwq
pull" then

   guix pull --commit=$(git -C ~/.cache/guix/<long-hash> \
                                   --before=$(date --date='2 weeks
ago' +%Y-%m-%d) \
                                   --format="%h" | head -n1)

And when I want to install something from one of the branches, it depends:

  a- inside "guix environment guix" and ~/src/guix/wk/<name>
       ./pre-inst-env guix install foo -p /tmp/profile
and then I use this /tmp/profile as any other.  Or I go with "guix
environment".  Well, if it is something I want to hold, then I write
down the manifest and channel files.

 b- inside "guix environment guix" and ~/src/guix/wk/<name>
       ./pre-inst-env guix pull --branch=<name> --url=$PWD -p ~/tmp/<name>
       /tmp/<name>/bin/guix blabla
and I almost never track "permanently" such other guix.

For custom packages, I am more often using '--load-path' than 'channel'.

Last, I use more and more "guix time-machine".  Well actually more
than b-, which I only use to test patches about "guix pull".  Roughly
speaking,
 - "guix environment" creates temporary profile
 - "guix time-machine" create temporary pull
And with this new "authentication" of "guix pull", I think now, it
would be better to do:
       guix time-machine --branch=<name> --url=~/src/wk/<name> -- blabla


Well, I do not know if all this is the correct way.  But it is more or
less what I am doing to avoid annoyance.


All the best,
simon