RSH 22: resolving git conflicts

Video

Collaborative notes taken during the session

Git conflicts

Session outline

• What is a conflict in git

  • example repository: https://github.com/ResearchSoftwareHour/demo-git-conflict
  • is a conflict bad?

• How to understand conflicts

  • graph on GitHub: https://github.com/ResearchSoftwareHour/demo-git-conflict/network
  • graph on GitLab: https://gitlab.com/bast/demo-git-conflict/-/network/main
  • git graph $ git config --global alias.graph "log --all --graph --decorate --oneline"
  • view your ("ours") changes separately
  • view their ("theirs") changes separately
  • when to expect a conflict:
    • two branches modified same portion of the code in two different ways
    • one branch modified a file, another branch deleted the file
  • when not to expect a conflict
    • modify different portions of the same file
    • one modification is ancestor of the other modification

• How to minimize conflicts

  • communication
  • keep branches as focused as possible
  • keep branches as short-lived as possible
  • pull before you do new work

• Useful config

  • $ git config --global merge.conflictstyle diff3
  • I have in my .gitconfig:

  [merge]
      conflictstyle = diff3
      tool = meld
  [mergetool]
      keepBackup = false
  [mergetool.meld]
      useAutoMerge = true
  

• Our general strategies

  • Resolve it the classic way
  • Decide "these do the same thing" and keep the more recent/active branch version
  • Recognize that one branch is "better" and keep one of the two (see later: ours/theirs), maybe transplant few changes manually on top

• Locally

  • example: we clone https://github.com/ResearchSoftwareHour/demo-git-conflict
  • merge conflict resolution on command line
  • git status and git diff in a conflicting merge
  • most scary of the methods
  • visual tools

• Ours/theirs strategy

  • on all conflicting files

    $ git merge -s recursive -Xours somebranch
    $ git merge -s recursive -Xtheirs somebranch
    

  • ours/theirs on only few files

• Conflict resolution on the web

  • GitHub
  • GitLab

• How to abort a conflicting merge

  • a merge/rebase only modifies my current branch, never the other branch
  • how to check whether it will conflict

• What is git rebase

  • how a git rebase differs from a git merge: https://coderefinery.github.io/git-branch-design/01-rebase/
  • rebase is not a free ticket out of a conflict: show how to resolve when rebasing
  • conflicts appear separately, one by one, instead of all in one as in a merge conflict

• Other strategies

Questions/comments

• Research Software Hour intro tune can be found at: https://soundcloud.com/w-m-vanvliet/research-software-hour-intro-tune

  • Licence CC-BY, feel free to remix and make better
  • Note: Quality is very bad because of how we played it, we need solve this for next time.

• Nice that you are back! My question is: Does this git graph command work always? Or does it need special packages on the host cluster, please?

  • It's an alias, it adds some extra options to "git log" so always works. Well, maybe not on very old git, but all the options are pretty old.

• Rebase means just to attach a branch somewhere else to the head, please? Or at least at another position of the main (?) branch, please?

  • Yes, basically transplanting part to another. As you might expect you can do lots of different things...

• Does it have to be always main or could it be also another branch?

  • ... like attach it to a different branch, different commit, etc. There are --onto options, and upstream and branch. More than anything I learned about it by playing with it some.
  • any branch, git rebase somebranch means move commits from my current branch which are not on somebranch behind somebranch