Re: [eigen] Bitbucket is dropping its Mercurial support!

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi!

On 24/08/2019 12.30, David Tellenbach wrote:
> just some thoughts about some points you've made:
>
> > b) Fixing internal links inside commit messages ("grafted from ...", "fixes error introduced in commit ...")
> Maybe I've forgot something crucial but doing something like
>
> for branch in $(hg branches | awk '{print $1}'); do
>      hg update -C  $branch > /dev/null
>      echo "$branch $(hg log -v | egrep "bitbucket.org" | wc -l)"
> done
>
> gives me
>
> Branch                       Links
> ------                       ------
> default                      9
> [...]

The point you missed is that especially the "grafted from" links do not 
include the full URL, just the hg-hash (which is different from 
git-hashes). And just greping for "grafted from" gives me 425 results 
(in total -- if you want the log of individual branches, you need to use 
the `-b` option).
For a more precise count, you should grep for hexadecimal numbers longer 
than a few digits inside the commit messages.

I somewhat doubt that any existing hg->git converters automatically 
translates these hashes, but I'd be very happy if someone finds out 
otherwise. Changing these manually is definitely not an option.

Also, if we stayed with mercurial, but used a different provider, we 
can't modify the history, because that would influence all the hashes 
(but then only the 9 direct links to "bitbucket.org/..." you found would 
be broken, which is acceptable, IMO)

Of course we can just ignore these links (though I think broken 
links/hashes are even worse than non-existing ones ...)

> Another point are links inside the codebase that point to bitbucket.
>
> Following the same logic as above I use
>
> hg grep "bitbucket.org"
>
> and get 11 links (all seem to be the same). Again something fixable manually.

Agreed, this part is easy to fix manually.

> > c) Fixing external links to the repository. Most notably, any links from our bugtracker will eventually fail (even if we stayed with bitbucket, the hashes won't match). I doubt that we could set up any automatic forwarding for that.
> This might be by far the most complicated point since a lot (the majority?) of all issues contain links to commits. If desired I can find a concrete number but I doubt that it will be very...motivating. I also doubt that Bitbucket will provide any functionality to redirect links to other Git providers but I could image that there could be some workaround if we decide to migrate to Bitbucket Git. Something we should keep in mind before choosing a new provider.

If you (or anyone else) are/is really interested, I can try to make a 
MySQL dump of the underlying database (I'd need to strip the user data). 
If we have some automatic translation between the hashes, this could 
even allow us to automatically convert all links.
Migrating to bitbucket-git will still break all existing links, since 
the hashes don't match. And as bitbucket is not even planning to provide 
an automated repository conversion, I would not count on any kind of 
forwarding mechanism.


> > Any third-party which relies on our main repository will need to change as well (not directly "our" problem, but we need to give a reasonable amount of time for everyone to migrate to whatever will be our future official repository).
>
> It's currently unclear for me what exactly will happen with the hg repo but I guess it will be archived or something similar. In this case we can link to the new repo on the README page. I don't have any further ideas regarding this but also think we should migrate somewhat fast.

Yes, I think this is unclear for everyone at the moment. The 
announcement from bitbucket sounds a lot like they will literally delete 
all hg-repositories in June next year :(
If it was at least frozen/archived as it is, we would have almost no 
problems with point c).

For manual redirection, we can of course open a new git-project which 
just contains a README.md saying that bitbucket dropped hg-support, and 
point to where Eigen migrated to.

> > I see essentially three options:
> > 1. Migrate to another mercurial provider
> > 2. Convert to git, stay at bitbucket
> > 3. Convert to git, migrate to another provider
>
> 1. We could migrate to Tuxfamily and keep mercurial. As you said this would imply we have to handle pull requests separately which is possible. As you surly know LLVM does exactly that by using Phabricator. However this would fix some of the issues above but links to bitbucket would remain a problem. Another downside of mercurial is that only very few projects are using it and contributing would be much easier in the case of git.

I really don't see much difference in usability between hg and git -- 
both have their advantages and little quirks, IMO. And I don't think 
that hg was ever the main-hurdle for people contributing to Eigen ...

If Phabricator allows to import our existing PRs that would of course be 
a nice option. But I'm really pessimistic about that at the moment, 
since this also requires to match all users which made the PR or took 
part in the discussion to the new host (maybe that would be the only 
argument for staying with bitbucket).


> 2. The only reason I see for this is the one I mentioned above: If there is (or will be) any support to redirect bitbucket links it will most likely only work if we stay at bitbucket. Compared with other code hosting services I find bitbucket (not mercurial) to be really complicated and not intuitive.

It might be an option, if they allowed to automatically migrate 
pull-requests. But at the moment, they don't even seem to plan automatic 
migration of repositories.

> 3. In an ideal world this would be my absolute preference (not very surprising). Regarding the choice of a service I want to make the personal point that I would rather migrate to Gitlab than to Github because it is as least as good as Github and I think that diversity of tools and providers is crucial for open source. In the long run we could even think about migrating issues to Gitlab and installing test runners (this is another story).

In my ideal world, somebody volunteers to do the work necessary for 
migration :) -- including the issues I pointed out (doesn't have to be 
the same person doing everything, of course). Even some proof-of-concept 
demos what can be automated would be nice!

I don't have any real preferences between mercurial/git or 
github/gitlab/bitbucket.

I totally agree that having automated test runners on pull-requests will 
be a big plus (for which I'm even willing to sacrifice some of my 
original points, especially since we may need to anyway).

Cheers,
Christoph


> Thanks,
> David
>
> > On 21. Aug 2019, at 14:53, Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Hello Eigen users and contributers!
> >
> > As some may have noticed, bitbucket/atlassian is "sunsetting" its mercurial support:
> >
> > https://bitbucket.org/blog/sunsetting-mercurial-support-in-bitbucket
> >
> > If they stick to their timeline, we will have to migrate until June 1st, 2020. That means we still have time, but if we do nothing, things will break ...
> >
> >
> > Converting the repository itself to git should not be a bigger issue -- and if we do this we could as well migrate to a more mainstream provider (i.e., github).
> >
> > I think the main problems for migration are:
> > a) Migrating open pull-requests (for historical reasons, the closed/merged ones should probably be archived as well)
> > b) Fixing internal links inside commit messages ("grafted from ...", "fixes error introduced in commit ...")
> > c) Fixing external links to the repository. Most notably, any links from our bugtracker will eventually fail (even if we stayed with bitbucket, the hashes won't match). I doubt that we could set up any automatic forwarding for that.
> > d) Any third-party which relies on our main repository will need to change as well (not directly "our" problem, but we need to give a reasonable amount of time for everyone to migrate to whatever will be our future official repository).
> >
> > Smaller issues (relatively easy to fix or not as important):
> > e) Change links from our wiki (to downloads)
> > f) Change URLs for automated doxygen generation and for unit-tests
> > g) Automatic links from the repository to our bugtracker (currently "Bug X" automatically links to http://eigen.tuxfamily.org/bz/show_bug.cgi?id=X)
> > h) Change hashes in bench/perf_monitoring/changesets.txt
> >
> > I probably missed a few things ...
> >
> >
> > I see essentially three options:
> > 1. Migrate to another mercurial provider
> > 2. Convert to git, stay at bitbucket
> > 3. Convert to git, migrate to another provider
> >
> > Honestly, I see no good reason for option 2. And the only real reason I see for option 1 would be that it safes a lot of hassle with b) and h) -- also perhaps it would simplify c) (e.g., we could easily crawl through our bugzilla-database and just replace some URLs).
> >
> >
> > Any opinions on this? Preferences for how to proceed, or other alternatives?
> > Does anyone have experience with migrating from hg to git? Or migrating between providers? Especially, also dealing with the issues listed above.
> > Does anyone see issues I forgot?
> >
> >
> > Cheers,
> > Christoph

--
 Dr.-Ing. Christoph Hertzberg

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