Git ignore doesn't prevent things from being committed it just prevents them from being "tracked" (for lack of a better word) by default. If you manually explicitly add the file to a commit, and then commit the file will be tracked despite matching the ignore

You can always have local ignore files too (like for your personal IDE or whatever)

Well, if you're the build tool that creates that build-folder, then it just means you don't need to bother your user with adding it to the root gitignore.

One time, I implemented it for basically a repo-specific download cache folder. Ideally, my users don't need to know of that folder at all.

Or recently, I implemented it for a build tool where my users might not be devs. They might not use Git at all, or not be very adept at it, so I'm glad to not need to document it...

.gitignore doesn’t prevent things from being committed. It just tells git to ignore files that aren’t already being tracked. And you can easily override that with -f. Putting .gitignore inside of .gitignore will ignore itself (if it’s not already tracked).

If you're an end user, not a build tool, you'd rather want to place that in .git/info/exclude inside the repo. It's effectively another gitignore file, which won't be committed.

But if you do need something like this for a build tool, then yeah, you can create a file /test/.gitignore with these contents:

real-person-first-last.json
.gitignore

Then running git add . just adds /test/fake-person-first-last.json.

Both /test/.gitignore and /test/real-person-first-last.json would be ignored right away.