Re: RFC: Between git-subtree and git-submodules

On Sat, Jul 24, 2010 at 2:57 AM, Avery Pennarun [off-list ref] wrote:

On Fri, Jul 23, 2010 at 8:13 PM, Santi Béjar [off-list ref] wrote:

quoted

 First my requirements:

1) Everything[a] must be available from the same repository/branch (so I'm not
  worried about repository size)
2) The history must be as clean as possible
3) The directory content must be equal to the external module, at least when
  you add/update it[b]
4) The external module should be able to switch back and forth between
  different versions.

[a] Everything means all that you need to checkout all the commits in the
superproject not in the submodule.
[b] A consequence of #3 is that I lose all
change I've made in the subdirectory, if they are important I have to extract
them, apply them and add the module back.

git-submodule is rule out because of #1 but accomplish #2, #3 and
#4. git-subtree is rule out because of #2 (even with --squash).
[It fails at] #3 and #4
without --squash but accomplish #1 and #4 with --squash. So I need something
in between or a mixture of both.

I admit to having had some trouble parsing the above, so I moved some
punctuation marks around.  Please let me know if I've made a mistake.

If I understand correctly, you're claiming (indirectly) that
git-subtree without --squash does not accomplish #1.  I don't see how
this is the case.  Am I misreading?  I think git-subtree accomplishes
#1 in both modes.

Yes, git-subtree accomplishes #1 in both modes. --squash only applies to #4.

I don't understand what you mean when you say (#2) git-subtree doesn't
keep your history "as clean as possible."  What is "as clean as
possible" and what part of git-subtree's history results don't you
like?  (Of course it's very different with and without --squash.)

With git-subtree you always have the subtree history (even if it is
squashed). So when you merge a second time the submodule you get the always
the history of the subtree (even with --squash). So you basically always have
at least two branches while examining the history. Compare this
squashed history:

$ git log --graph --oneline
*   bb2dc25 (HEAD, master) Merge commit
'08b917ee90ecfd7b666364fe4ebb92aee5cdd2f7'
|\
| * 08b917e Squashed 'latex/' changes from ea35faf..895916a
* |   9de91f1 Merge commit 'b1b4c36bb8358582a6a20bb500bf98421428e2ca' as 'latex'
|\|
| * b1b4c36 Squashed 'latex/' content from commit ea35faf
* ea35faf Indent, whitespaces,...

with this pruned history:

$ git log --graph --oneline
* 8703aec (HEAD, master) Subtree 'latex/': 895916a Add files subcommand
* a942284 Subtree 'latex/': ea35faf Indent, whitespaces,...
* ea35faf Indent, whitespaces,...

But I understand that it can only be this way because of #3.

With #3, I can see that you want something different than I do; you
want to silently revert your own patches out of the submodule's
history, when you upgrade the submodule to a new version.  Personally,
I find this concept a bit objectionable (it's like "git merge -s
ours"), but okay, it's pretty easy to implement, and you've submitted
a patch to git-subtree that does it.  My question is: why would you
want this?  Isn't it clearer to 'git revert' the patches you don't
want?

I prefer to do all the modifications in an external repository, even if at the
end it is really a fork of the upstream repository. I think the proper place
to modify the files in a subtree is in an external repository.

And for #4, it's true that git-subtree without --squash does not allow
you to easily rewind to an older version of the submodule, while with
--squash it does.

It sounds to me like, if we added your patch to git-subtree, then
git-subtree --squash would solve #1, #3, and #4.  And maybe we could
fix #2 as well. Correct?

My patch does not change the behavior of --squash, it adds --prune.

Thanks,
Santi