Wireshark · Wireshark-dev: Re: [Wireshark-dev] Quick start instructions for Gerrit

[Evan Huus <eapache@xxxxxxxxx>]

On Fri, Jan 31, 2014 at 2:22 PM, Guy Harris <guy@xxxxxxxxxxxx> wrote:
>
> On Jan 31, 2014, at 10:26 AM, Evan Huus <eapache@xxxxxxxxx> wrote:
>
>> On Fri, Jan 31, 2014 at 12:44 PM, Guy Harris <guy@xxxxxxxxxxxx> wrote:
>>>
>>> On Jan 31, 2014, at 2:22 AM, Roland Knall <rknall@xxxxxxxxx> wrote:
>>>
>>>> But one clarification. You do not check-out a project with git. This
>>>> is a misconception. You clone the complete repository of wireshark
>>>> into a local copy.
>>>
>>> Unfortunately, yes, that's what happens, imposing a requirement to push changes after they're committed, and adding an extra step to my workflow with no obvious benefit either to me or to the project.
>>>
>>> I have, occasionally, been tempted to see whether I could do my own set of porcelain that allows me to completely ignore the "you have your own separate repository" stuff, with a more CVS/SVN-like model, where
>>>
>>>        1) there's an "update" operation that grabs from the master changes made since the last time a checkout or update was done, attempts to merge them into the files you have modified, and keeps track of the ones where there was a merge conflict;
>>
>> "git pull"
>
> ...which refuses to do the pull if there are any files differing from the checked-in versions, so, for me, the operation is actually
>
>         git stash; git pull; git stash apply
>
> which is in ~/bin/git-update so I can just do "git update".
>
>>>        2) there's a "commit" operation that sends your changes to the master;
>>
>> "git pull && git commit -a && git push"
>>
>> with the caveat that the push should be to gerrit, not straight to master
>
> (The caveat being, of course, Wireshark-specific; it's not the only project using Git with which I'm involved.
>
> And the caveat needs to be automated in some fashion, whether it's a ~/bin/git-checkin script that does all of the above or a way to configure Git so that pulls come from the master and pushes go to Gerrit.
>
> And the "git pull" would, of course, have to be replaced by "git stash; git pull; git stash apply", as per the above.)
>
>>>        3) changes are either committed to the master or they're not - there's no notion of adding a file that's already in the repository to a change set, and the "diff" operation shows the difference between all your changes and the master.
>>
>> As long as you use "git commit -a" this is basically already true
>> (with the exception adding new files or removing old files from the
>> repo).
>
> ...and as long as Git doesn't commit anything itself as a result of any of the aforementioned operations.
>
>> The ability to manage many small changes is a motivator for the
>> branching design, though this is perhaps less obvious. Consider a
>> situation where you may have several changes under development/review
>> at once, on a large project like the kernel (or Wireshark, for that
>> matter). In SVN you would probably just have a separate working dir
>> for each. Pros are extremely fast switching between environments (just
>> a 'cd' and you're done). Cons are disk space usage,
>
> Not a *huge* problem for me, personally.  (Most of the disk space on my laptop is, I think, taken up by a pile of virtual machines.)
>
>> and it is
>> expensive to set up another change (since it requires copying/building
>> the whole project, which is slow).
>
> Not too painful on my machine, either.
>
>> The other option is to keep all changes in one working directory and
>> let users switch between them. Pros are much-reduced disk space, and
>> near-instantaneous creation/deletion of branches. The con is that it
>> takes slightly longer to switch branches since doing so requires a
>> partial rebuild. However when the branches are closely related the
>> rebuild cost is usually a tiny fraction of the cost to rebuild the
>> whole project.
>
> The other con is that it's the moral equivalent of tabbed browsing, which I, at least, *really hate*, as it keeps a bunch of unrelated things in the same space.  (As per an earlier comment of mine, if Safari had an option to prevent it from even accidentally creating a tab, I would enable it in a heartbeat.)
>
> And does that work if your work is not committed until it's time to push to the official repository?  If not, it's another case of Git strongly pushing a particular workflow....
>
>> If you only ever work on one change at a time in a given working directory, and
>> you always push that change before starting another one, then there's
>> no reason to use branches.
>
> That's exactly my workflow, so there's no reason for me to use branches.

There is, I think, one more workaround required for this to be true,
though this one is due to Gerrit's cherry-picking behaviour, not git
proper. *sigh*.

If you make a commit and push it to gerrit, then submit that change,
the SHA of the final merged commit will be different from the SHA you
pushed because Gerrit amends the commit to add information about the
review process. This means when you pull git will see two commits with
identical changes but different SHAs and merge them (the merge will be
successful since the changes are exactly the same). You will then have
to reset to origin/master in order to discard the useless duplicate
commit and merge.

So if you have git-review installed, the commit step actually works out to:

$ git stash && git pull && git stash apply && git commit -a && git review

# submit the change on gerrit

$ git stash && git pull --no-edit && git reset --hard origin/master &&
git stash apply

# caveat, adjusting the argument to git reset as appropriate if
working on master-1.10 or master-1.8 instead of master.

"Beware of bugs in the above code; I have only proved it correct, not
tried it." --Knuth