From:  Kartikaya Gupta <kgupta@mozilla.com>
Date:  10 Oct 2018 20:16:43 Hong Kong Time
Newsgroup:  news.mozilla.org/mozilla.dev.planning
Subject:  

Re: comm-central future as a branch

NNTP-Posting-Host:  63.245.210.105

I believe that script is maintained by the Mozilla releng team, so
you'd have to talk to them to get a new git repo set up.

It's not clear to me if you'd have two git repos (one for the
mozilla-central stuff, and one pulls in just the comm/ folder) or a
single repo. In the latter case it sounds like it would be a brand new
conversion of mozilla-central from hg to git, which sounds kind of
undesirable given that we already have
https://github.com/mozilla/gecko-dev and
https://github.com/mozilla/gecko which are two different conversions
of m-c to git. I don't really know what the best way forward here, I
just wanted to mention this because if you want searchfox to keep
working we'll need some sort of git repo with the code.

Also, my messages are getting stuck in the dev-planning moderation
queue so I'm cc'ing Magnus directly here.

Cheers,
kats

On Tue, Oct 9, 2018 at 12:51 PM Ben Bucksch  wrote:
>
> Hey kats,
>
> just a quick thank-you note for providing searchfox :)
>
> I think we'd need a new git repo, but that it would work like the old,
> just that it already contains mozilla code, so it should be simpler,
> actually.
>
> The main trick is that whatever script pushes to github needs to be adapted.
>
> Ben
>
> Am 10/9/2018 um 6:32 PM schrieb Kartikaya Gupta:
> > Have you given any thought as to what would happen to the git mirror
> > of the comm-central repo that currently lives at
> > https://github.com/mozilla/releases-comm-central ? I ask because
> > searchfox uses this git repo to do the indexing of comm-central and
> > that might break with these changes. If you care about still having
> > searchfox indexing available for comm-central after this change it
> > would be good to continue having some sort of git mirror. If it's a
> > brand new git mirror with different hashes we'll have to rebuild the
> > blame repo and any comm-central permalinks (in bugs, etc.) will likely
> > break. Or we can try harder to keep permalinks working by mapping the
> > old hashes to the new ones but that's more work.
> >
> > Cheers,
> > kats
> > On Tue, Oct 9, 2018 at 11:48 AM Ben Bucksch  wrote:
> >> I like this idea. I'm in favor.
> >>
> >> If I understood correctly, you're proposing to take a mozilla-central
> >> (or a mozilla-unified) repo, put comm-central checkout into the comm/
> >> subdirectory, and push that to the branch "comm/default". I think that's
> >> the right way to do things, yes.
> >>
> >> We do not even need buy-in from Firefox people, because hg is a
> >> distributed system, so we can simply have our own repository that
> >> contains a copy of mozilla-central plus comm/ (from former comm-central).
> >>
> >> I'm also in favor of re-adding CVS history. It's important for us, more
> >> important than for Firefox, due to the longevity of our project.
> >>
> >> As for "which combination of mozilla and thunderbird is building and
> >> working?", I would suggest to make a branch comm/bleeding where we merge
> >> mozilla-central immediately and completely without tests. So, if there
> >> are API changes in Mozilla and Thunderbird hasn't been updated yet, it
> >> will be broken. (Code-wise, this is what we currently get, by checking
> >> out mozilla-central and comm-central independently.) So, you have the
> >> option of easily continuing to check out the latest and bleeding edge.
> >> Then, once we tested the combination and we confirmed that it's working,
> >> we merge comm/bleeding into comm/default, and it becomes the new
> >> official Thunderbird development branch. This way, fixing an API
> >> breakage becomes a hg commit that fixes the API and hg merge operation.
> >>
> >> The main advantage of this setup is that it's clear which version of
> >> Mozilla works with which version of the Thunderbid code, down to the
> >> commit level. And we capture this information using the version control
> >> system itself, but with some build scripts.
> >>
> >> That should dramatically simplify development and build scripts.
> >>
> >> Ben
> >>
> >>
> >> Am 10/9/2018 um 10:06 AM schrieb Magnus Melin:
> >>
> >>> I'd like feedback on the below plan for having Thunderbird in a single
> >>> repository.
> >>> Let's have follow-ups go to dev-planning
> >>>
> >>> TL;DR version: planning to have current comm-central live as a branch
> >>> instead of a separate repository.
> >>>
> >>> ---
> >>>
> >>> Background
> >>> ----------------
> >>>
> >>> When the Mozilla move from CVS to hg took place in 2008, the code
> >>> related to Thunderbird was not included in mozilla-central and instead
> >>> placed in the comm-central repository. Under the hood Thunderbird uses
> >>> the mozilla-central code, so to build it currently has to check out
> >>> both repositories. This is not ideal, for many many reasons.
> >>>
> >>> I wrote [an email to
> >>> maildev](http://lists.thunderbird.net/pipermail/maildev_lists.thunderbird.net/2017-November/000875.html)
> >>> last year listing some of the drawbacks of this setup - but
> >>> essentially what it comes down to is that version control was not
> >>> meant to be used like this and it makes workflows error prone, in
> >>> addition to having to do various hacks in the build automation.
> >>> Enabling autoland, phabricator and other tools used by Mozilla core
> >>> could also be done much more easily for comm-central with a single
> >>> repository.
> >>>
> >>> The mail spurred some related discussion on git vs hg and importing of
> >>> history, but basically there was agreement among the comm-central
> >>> developers to go ahead with this change.
> >>>
> >>> Thunderbird has now migrated its build automation to Taskcluster, and
> >>> also moved to building with mozilla-central as topdir, with a comm/
> >>> sub-folder containing comm-central code. (We used to instead have a
> >>> mozilla subdir checkout of mozilla-central as child the comm-central
> >>> checkout.)
> >>>
> >>> In 2014 there was [a proposal to merge comm-central code into
> >>> mozilla-central](https://groups.google.com/forum/#!msg/mozilla.dev.planning/P8oHKTCWSiQ/76ECituhK-IJ)
> >>> but this was rejected since the powers that be did not want 1) the
> >>> confusion about what code belongs to what project, 2) pull/tree size,
> >>> and 3) it was seen as irrelevant to Firefox. The proposal below has
> >>> none of these obstacles, and depending on the physical repository
> >>> location, may not change anything at all for a Firefox developer.
> >>>
> >>> I think it's now time to revisit the single repository idea and pull
> >>> that through in one way or the other. So, on to the proposal. For
> >>> reference, on disk comm/ is on currently 122 MB (+ comm/.hg 192 MB),
> >>> so size-wise it is comparatively small, with a mozilla-central
> >>> checkout weighing in at 2.3 GB. Including the relevant CVS history,
> >>> the comm/.hg would be 317 MB in total.
> >>>
> >>> How
> >>> ------
> >>>
> >>> To capture the essence of what Thunderbird is, we would make
> >>> comm-central a named branch of the mozilla-central. Let's call this
> >>> branch "comm/default".
> >>>
> >>> Initially, we'd pull in a hg converted version of the current
> >>> comm-central default branch, putting all the files into a comm
> >>> sub-folder in the base directory of the comm/default branch. This is
> >>> the way that the Thunderbird build system already wants the code laid
> >>> out. With the comm sub-folder it will be clear to everyone involved
> >>> which code is on mozilla-central code and which is not. It is possible
> >>> to import the CVS history for the related directories too while we're
> >>> at it, but it adds some size. Importing related CVS history only adds
> >>> around 125 MB extra so I'm inclined to include it. With the new
> >>> comm/default branch pulled in, we merge the curent mozilla-central
> >>> default branch to comm/default. The resulting code is now the same as
> >>> status quo (of the both repos pulled in), just that it's all version
> >>> controlled in the same repository.
> >>>
> >>> Once this is all set up, Thunderbird development work would move on on
> >>> the comm/default branch, and there would be periodical merges with the
> >>> (mozilla-central) default branch. These merges could be automated if
> >>> wanted.
> >>>
> >>> Quite often it's the case that Thunderbird code needs to be adjusted
> >>> to build, due to changes in mozilla-central code. For cases of known
> >>> incoming bustage Thunderbird now would have the possibility of waiting
> >>> to do the merge until a fix is available. I would suggest never to
> >>> back out bustage causing mozilla-central changesets from the
> >>> comm/default branch, but to detect other incoming bustage by doing
> >>> builds from a comm/band-aid branch (branced from comm/default). The
> >>> details on this can be discussed later though, not to derail
> >>> discussion about the main issue here. There are many alternatives, and
> >>> it's also completely possible to do what we currently do.
> >>>
> >>> Where
> >>> ---------
> >>>
> >>> In the earlier discussions i's become clear there is a bunch of
> >>> confusion around what is a branch and what is a repository, so please
> >>> note the difference. Aa repository is the physical location where the
> >>> history of a project is stored. Every repository does not have to
> >>> carry every branch. I.e., the mozilla-central repository could carry
> >>> the comm/default branch, or the comm/default branch could exist only
> >>> in a comm-central2 repository somewhere else. In all cases it's
> >>> trivial for developers who have mozilla-central checked out, to add
> >>> the comm/default branch to their local checkout.
> >>>
> >>> So for the location there are at least three options:
> >>>
> >>> A: branch in the mozilla-central repository
> >>> B: branch in the mozilla-unified repository
> >>> C: branch in a repository elsewhere
> >>>
> >>> Not to disrupt operations too much I think it would be preferable to
> >>> use option B - create the branch in the mozilla-unified repository. It
> >>> does depend a bit on what plans Mozilla has for these repositories.
> >>>
> >>> Creating the branch in mozilla-unified of course needs buy-in from the
> >>> Mozilla hg people, so please let me hear your opinions.
> >>>
> >>> What about history?
> >>> --------------------------
> >>>
> >>> For the proposed approach (going through `hg convert`) commits are
> >>> preserved, but AFAIK it's not possible to preserve actual commit
> >>> hashes. `hg convert` will graft the original commits, and this adds
> >>> the original hash as an extra field to the new commit (use `hg log
> >>> --debug` to see it). I don't think this is such a big problem. The
> >>> original commits would be linked in the pushlog, the same way there is
> >>> "converted from" for mozilla-central-cvs, like
> >>> https://hg.mozilla.org/experimental/mozilla-central-cvs/rev/ab117d946959.
> >>> I don't see them e.g. in
> >>> https://hg.mozilla.org/users/mkmelin_iki.fi/thunderbird-central/rev/8f8b0933b611
> >>> so perhaps there is some server side feature that needs turning on?
> >>>
> >>> Can I try it?
> >>> ---------------
> >>>
> >>> You can check
> >>> https://hg.mozilla.org/users/mkmelin_iki.fi/thunderbird-central/ which
> >>> carries the comm/default branch.
> >>>
> >>> In your mozilla tree, pull in the branch like this:
> >>>
> >>>       hg pull -u -b comm/default
> >>> https://hg.mozilla.org/users/mkmelin_iki.fi/thunderbird-central
> >>>
> >>> To completely remove it again, use `hg strip "branch(comm/default)`
> >>>
> >>> How did you do it?
> >>> ------------------------
> >>>
> >>>      CVS_GIT_REPO=~/tmp/mozilla-cvs-history/
> >>>      CC_HG_REPO=~/Code/tb/mozilla/comm/
> >>>
> >>>      git clone https://github.com/ehsan/mozilla-cvs-history.git
> >>> $CVS_GIT_REPO
> >>>
> >>>      echo default comm/default | tee branchmap.txt
> >>>      echo rename . comm | tee filemap.txt cc0.txt
> >>>
> >>>      hg --cwd=$CC_HG_REPO up 0
> >>>      (cd $CC_HG_REPO && ls -d */ | cut -f1 -d'/' | sed 's/^/include /')
> >>>>> cc0.txt
> >>>      hg convert --filemap=cc0.txt --branchmap=branchmap.txt
> >>> $CVS_GIT_REPO single-repo/
> >>>
> >>>      CVS_TIP=`hg id --cwd=single-repo -i -r tip --debug`
> >>>      CC_0=`hg id --cwd=$CC_HG_REPO -i -r 0 --debug`
> >>>      echo $CC_0 $CVS_TIP | tee splicemap.txt
> >>>      # e4f4569d451a5e0d12a6aa33ebd916f979dd8faa
> >>> 93dd94bad983ce2eff5f228719c349b78a8a7f7d
> >>>
> >>>      hg convert --config convert.hg.saverev=True
> >>> --splicemap=splicemap.txt --filemap=filemap.txt
> >>> --branchmap=branchmap.txt $CC_HG_REPO single-repo/
> >>>
> >>> For fun, see all the history down to 1999 is there, like
> >>>
> >>>      hg log comm/mailnews/mime/src/mimei.cpp
> >>>
> >>> Then go on and add the default branch from mozilla-central and do the
> >>> merge
> >>>
> >>>      cd single-repo
> >>>      hg pull -f -b default $CC_HG_REPO/..
> >>>
> >>>      hg up comm/default
> >>>      hg merge default && hg commit -m "Merge default to comm/default
> >>> branch"
> >>>
> >>>      hg push -f -b comm/default --new-branch thunderbird-central-push
> >>>
> >>> ---
> >>>
> >>> Thoughts, comments, feedback appreciated!
> >>>
> >>>   -Magnus
> >>>
> >>> _______________________________________________
> >>> tb-planning mailing list
> >>> tb-planning@mozilla.org
> >>> https://mail.mozilla.org/listinfo/tb-planning
> >> _______________________________________________
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