[GRASS-dev] git: how to switch between branches?

[Markus Neteler]

Hi Panos,

thanks so much for writing up this guide which looks very good to me
(and saves disk space; and offers an approach more close to those
freshly coming from SVN)!

Some comments + questions inline:

On Mon, May 20, 2019 at 10:23 AM Panagiotis Mavrogiorgos
<pmav99 at gmail.com> wrote:
>
> Hello Markus
>
> I don't have real-world experience with this, but I am not sure if changing branches and
> distcleaning/recompiling is the most convenient workflow. I think I would prefer to have
> multiple local repositories with different branches checked out. Thankfully git makes it
> rather easy to have this.  E.g.:
>
> 1. You create two root directories. One for Python2 and one for Python3:
>
>     mkdir /home/user/git/grass-p{2,3}
>
> 2. Create a virtualenv inside grass-p2 and grass-p3. E.g.:
>
>     cd /home/user/git/grass-p2
>     virtualenv -p python2 venv
>
>     cd /home/user/git/grass-p2

... I suppose, it should be
     cd /home/user/git/grass-p3

>     python3 -m venv venv
>
> 3. Clone the remote GRASS repo and name the local repo `dev`. You will only do this for `grass-p3`:
>
>     cd /home/user/git/grass-p3
>     git clone https://github.com/neteler/grass dev
>
> 5. For python 2 and for each release branch you will make a local git clone. This way
>    you won't be wasting disk space. Read more about this
>    [here](https://stackoverflow.com/questions/7187088/git-how-to-create-local-repo-with-symbolic-links-to-the-git-main-repo).
>
>     cd /home/user/git/grass-p2
>     git clone ../grass-p3/dev dev
>     git clone ../grass-p3/dev r72
>     git clone ../grass-p3/dev r74
>     git clone ../grass-p3/dev r76
>
> 6. The dir structure should look like this:
>
>     $ tree grass*
>
>     grass-p2
>     ├── dev
>     ├── r72
>     ├── r74
>     ├── r76
>     └── venv
>     grass-p3
>     ├── dev
>     └── venv

So far, so nice (locally, I used "master" instead of "dev" but that's
cosmetics).

> 7. On each release clone you need to checkout the respective branch:
>
>     cd /home/user/git/grass-p2/r72 && git checkout releasebranch_7_2

Now, here I cannot proceed:

cd $REPOPATH/grass-p2/r72 && git checkout releasebranch_7_2
error: pathspec 'releasebranch_7_2' did not match any file(s) known to git

git branch -a
* master
  remotes/origin/HEAD -> origin/master
  remotes/origin/master

Any ideas?

>     cd /home/user/git/grass-p2/r74 && git checkout releasebranch_7_4
>     cd /home/user/git/grass-p2/r76 && git checkout releasebranch_7_6
>
> 7. Each directory is a full blown git repo. It is only by convention that 7.6 backports
>    will happen in `r76` etc.  If you want to directly pull/push from/to github from the release
>    directories, you will probably need to setup remotes. Regardless, setting up remotes
>    etc should only be done once.

Yes.

> 8. Obviously, when 7.8 gets released, two more directories will need to be added (one
>    for python2  and one for python 3).

(...looking fwd to dropping Python-2 support)

> The benefit of this approach is that at least for trivial backports, you will not need
> to recompile everything and, perhaps more importantly, you will not need to recompile
> "master" in order to test a fix in 7.2.

Yes, that's pretty cool.

> all the best,
> Panos
>
> PS1. There are other ways to achieve something like this, e.g.
> [`--singlebranch`](https://stackoverflow.com/a/1911126/592289) but I don't see much
> benefit.
>
> PS2. You can optionally use something like [direnv](https://github.com/direnv/direnv) to
> automatically activate the virtualenvs when you cd into the corresponding directory.
> This way there is no confusion WRT which python is active. I use this and it works
> marvellously.

Wow, didn't know about that so far. As soon as I get the problem
mentioned above sorted out I'll try.

Best,
Markus