Discuss use of submodule for library

[jmshapir]

I'm opening this issue to discuss whether we might like to make /source/lib/JMSLab a standalone repository that is imported in Template as a submodule. For background see github blog, git docs, gist.

I'm assinging to @veli-m-andirin @rcalvo12 but anyone who has a view should feel free to weigh in!

[veli-m-andirin]

Thanks @jmshapir!

Here are my thoughts about this:

• I tried to think of the advantages that using submodules can bring:
  • I agree with the two points mentioned in gist, although I think the first point is not very relevant for us. (Template is not a huge repository, and source/lib/JMSLab makes a small part of it, so taking it out would not help the Template a lot. Moreover, most of our development efforts here is focused on source/lib/JMSLab, so we do not really have a pollution of commit history, i.e., majority of the commits concern that directory.)
  • In terms of the second point, here are my thoughts: The fact that people will not have to manually copy-paste the builders when we update them sounds nice. However, this also does not mean that any changes in submodules will be reflected in parent repositories automatically. git pull does not automatically update submodules, so one has to run git submodule update. I think this would require every user of a repository to do the same thing since git pull won't update the submodule for them either. Hence, there is still manual effort required, and that can become more complicated with every user having to enter an additional command rather than git pull.
• In terms of the downsides:
  • One thing that I appreciate about current architecture is that having copies of the builders in each repository also allows us to modify them depending on the needs of a project. (Consider the case we want to tweak some builders or modify executable names in a project but not in others.) I wondered if this functionality would be preserved if we use submodules. The answer is yes, but things seem to require additional care as per the discussion here.
  • Moreover, per the section "Switching to submodules" here, taking out an existing folder to become an external dependency requires some more effort compared to a clean start.
  • This is minor, but I don't know how well this functionality is represented in GitHub Desktop. When cloning a repository with submodules or updating submodules within a repository, the most basic commands such as git clone or git pull are not sufficient, so switching to submodules might require everyone to use the command-line client from time to time.

Overall, I think both the costs and the benefits are small, and I think the costs slightly exceed the benefits. (Or at least, the benefits don't seem large enough to necessitate a move.)

Curious to know your thoughts @jmshapir @rcalvo12.

[jmshapir]

@veli-m-andirin thanks! That sounds reasonable to me. I'll leave the issue open for a bit in case anyone has thoughts to add. Also, to be clear, this isn't pressing--just wanted to open the discussion while I was thinking about it.

[jmshapir]

Summary: In this issue we considered transitioning the python library in the Template to a submodule. Since no one has advocated in favor I am closing the issue, but we can reopen if someone wishes to take the other side!