Re: [topgit] tg update error

also sprach Junio C Hamano [off-list ref] [2009.02.13.0014 +0100]:

quoted

TopGit would need to make a proper branch, merge the bases into
it, merge that branch into the topic branch, and the probably
delete the branch pointer, as it's no longer needed and would
only pollute the refs/heads/* namespace.

So it happens purely inside TopGit and the end user never sees
a state that HEAD points outside refs/heads/, right?

Yes.

Why can't the base flipping operation you descibed be done on
detached HEAD?  Perhaps with a shell variable or two that hold
commit object names you need to keep track of while it is doing is
work?

I am not sure I understand. Isn't that what's currently happening?

Have a look at line 110 of tg-update.sh:

  http://git.debian.org/?p=collab-maint/topgit.git;a=blob;f=tg-update.sh;hb=HEAD#l110

But the end users don't.  If TopGit dies (or killed) during the base
flipping operation, doesn't the end user left in a funny state (granted, a
detached HEAD is also a funny state, but it is already a known funny state
they are familiar with.  HEAD that is a symref but points outside
refs/heads/ is a lot funnier).

If topgit is killed, yes, then the repo could be left in a funny
state. I suppose this could be addressed by putting proper traps in
place.

If the merge fails, however, then the user is advised what to do;
see lines 114ff.

You did not actually answer a larger question.

It wasn't asked to me before... ;)

What other undocumented features/restrictions does the code depend
on, that tightening them to help normal git users inadvertently
may cause breakages similar to this one in TopGit?

I think Petr would need to help out answering this.

I agree that it would be good to address each such occurrence in
turn and replace it with a method that only makes use of the public
API. Up until now, however,

  git checkout -q "refs/top-bases/$name"

was not really something undocmented or restricted. I find it rather
difficult to separate
public-as-in-every-user-can-and-should-use-this features from
restricted-better-be-left-alone-unless-you-really-know-what-you-are-doing
features with Git. This has gotten *a lot* better, but the fact that
I can still call e.g. git update-ref (as opposed to e.g. git
_update-ref)  and potentially turn my repository upside down
exemplifies this.

Maybe Petr remembers all the instances when he sneakily used tricks
to make things work, and then we can look at each of them in turn.

Maybe some of you could go through the code (which isn't /that/
much), looking for instances of not-so-public API abuse and help us
identify them too.

Cheers,

-- 
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