Say you have two git repositories that you want to combine into one.
Maybe you’re assembling a monorepo, or maybe you’ve decided your standalone tool/library shouldn’t be standalone any more. Whatever the reason, you almost certainly don’t want to lose your commit history.
So here’s how:
The important thing to realise is that while a git repository contains a graph of commits, the graph doesn’t need to be fully connected - you can have multiple distinct unconnected trees. If you’ve ever used GitHub Pages for a project then you’ve exploited this - it creates a totally disconnected
With that in mind, the whole process is fairly straightforward:
First, start with your target repo, and fetch in the commits from your source repo
Now your target repo has both trees in it
At this point, you might want to tweak your source a little (e.g. moving it into a subdirectory, shifting files around to avoid collision etc.)
Now go back to your target branch, and merge in the source!
Fancy things like subtree merges exist, and I’m sure there’s a neat one-liner that’ll do the whole shebang. For me this is a rare enough need that I’m likely to have forgotten the magic incantation, doing it “manually” costs little extra, and inevitably I want to fiddle with the source repository a little in the middle.
I find the whole process a nice reminder of the quite elegant and simple system at the heart of git.