I just renamed the title to more easily reflect the commits that are in here.

Well, that didn't work like intended...
I tried doing a git rebase -i HEAD~9, and changed the relevant picks to squash instead, but I'm unsure as to what that actually did. What am I supposed to do? Please excuse my inexperience

The right command is head git rebase -i @~9. I am not sure what you did now but it is not the right thing and merging master into a PR is a big no go.

(FWIW, HEAD~9 works fine.)

You first do the git rebase command you used. Then, you choose the commits you want to squash, but you must order them to come DIRECTLY AFTER the commit you want to squash them into. e.g.

pick asdf1 commit 1
pick asdf2 commit 2
pick asdf3 commit 3, intended to become part of commit 1
pick asdf4 commit 4, intended to become part of commit 2
pick asdf5 commit 5, intended to become part of commit 1
pick asdf6 commit 6, intended to become part of commit 1
pick asdf7 commit 7, intended to become part of commit 2

would become

pick asdf1 commit 1
squash asdf3 commit 3, intended to become part of commit 1
squash asdf5 commit 5, intended to become part of commit 1
squash asdf6 commit 6, intended to become part of commit 1
pick asdf2 commit 2
squash asdf4 commit 4, intended to become part of commit 2
squash asdf7 commit 7, intended to become part of commit 2

I usually use fixup instead of squash, since I don't care about the commit message most times.

I usually use fixup instead of squash, since I don't care about the commit message most times.

Actually this is what I do all the time, too but it is still called squashing.

but you must order them to come DIRECTLY AFTER the commit you want to squash them into

That's exactly what I did, so I don't know what I did wrong.

I am not sure what you did now but it is not the right thing and merging master into a PR is a big no go.

Are you referring to this pull request 971f2a1? If yes, I don't know how to avoid doing that. After the rebase git wanted me to pull changes for some reason, and since I had local unpushed commits, the merge emerged.

Is there a simple way to rescue this disaster? I'm thinking of attempting something like this, but figured I should probably ask someone who knows what to do before I screw things up more.

Another thing I could try is to start from scratch and redo the changes in the PR, but I'd like to learn how to do it properly too.

I learn from my mistakes ;)

You can take the changes from this PR, delete the branch, create it under the new name and commit the changes into 3 commits and then force push.

Instead of creating a merge commit, you usually want to git pull --rebase which will automatically rebase your local changes on top of wherever you're pulling from. If there are conflicts, you'll be able to fix them and git rebase --continue until your changes are "compatible" with wherever you pulled from.

@ofborg eval

I was able to fix the problem by rebasing a second time, and using git push --force to push the changes. I didn't use the force flag the first time, and that's probably why the commits didn't squash.

I have now added @romildo's suggested changes, some even in both files (like removing unneeded files, and not copying ${src} directly)