Day 6

Merging branches

If branch happens, then change happens. You are going to want to incorporate the work from your separate branch back into your main line of development. git merge and git mergetool are two tools to deal with the consequence of a branch being so easy to do!

Typically main is the branch designated to accept all merges, but YMMV. A merge results in a commit that has two+ parent commits.

Commands in Play

git merge
git checkout [main]
git diff main…bugfix -> § see below
git diff —name-status main…bugfix -> §§
git log -1 -> §§§
git merge —abort
git config

The output from git diff main...bugfix shows the difference between branches relative to when they became different. It’s a preview of what merge will do. The order is significant for it: “main” is listed first and appears on top (“the highway”), bugfix is listed second (“the on-ramp”).

Elementary fix, dear Watson. Don’t divide by zero in bash script 'baz'. — Elementary fix, dear Watson. Don’t divide by zero in bash script ‘baz’.

This command is overkill,in the example, but it demonstrates that bash script ‘baz’ (from bugfix) will be merged into main by the identifying glyph ‘M’. For large repositories, this command gives a useful summary of the actions that will be performed on merge.

Another sampling of “what was done” (after git merge). At the CLI, we have the SHA1 IDs that made up the merge commit. It’s the same in gitk, maybe a little easier to interpret\see.

GITK does not lack for the same info. See also the node connectors: color:red==main branch and color:blue==bugfix branch.

10.3.1 Dealing with merge that needs human

Now we will refresh\restart and append a printf statement to bash script ‘baz’ on branch main. Nothing has changed on branch bugfix. But we cannot auto-merge them via the tools.

Auto-merging baz
CONFLICT (content): Merge conflict in baz
Automatic merge failed; fix conflicts and then commit the 
result.

Having gotten this error, bash script ‘baz’ on branch main has been altered, and it was altered with the glyphs denoting the local change <<<<<< HEAD and the remote change >>>>>> bugfix. We can see what happened and adjust bash script ‘baz’ to take the preferred code.

Bouncing the conflicted merge thru VS Code (not shown) was an interesting, but mid-to-heavyweight action.

10.3.4 Aborting a merge

Short\Easy mode: If you are mid-merge and in a moment of realization that you have selected incorrectly, you can perform a git diff to see the conflicted hunks and abandon it via git merge --abort if necessary. Chap 16 covers revert, or to take back, a merge.

10.4 Performing fast-forward merges

Definition: The fast-forward merge takes effect when the target branch is a descendant of the branch that it will merge with. /Once Git detects that the branch being merged is a direct descendent of the current branch, it moves the local branch up on the remote branch–a fast forward to main!/

10.6.2 Changing how conflicts are displayed (merge.conflictstyle)

Enable this configuration (using git config) to subtly change the way conflicting hunks are displayed in a file.

Performing octopus merges

An octopus merge is a merge that consists of more than two parents.

References

How to use VS Code as your Git editor, difftool, and mergetool
/I had not configured a difftool nor mergetool in ~/.gitconfig The blog post, above, ☝️ was a useful reference. I briefly considered using graphical comparison tool (i.e. bcomp4), too!/
HOW TO RESOLVE CONFLICTS from git merge command documentation
octopus-merge README.md
Kindly forked from code ocelot ☝️. This README as explainer for “famous octopus merge”.

Last updated on Feb 1, 2022