Ignore a versioned file from a Git repository and its clones

Question

For some reason, I would like to have an empty file on my repository. The file needs to exists, but the build process changes it, and I do not want those changes to be committed. I need that users that clone my repository ignore changes on this file too.

git update-index --assume-unchanged seems good, but it only works locally.

Do you know how I can solve this ?

Answer 1

The clean filter approach mentioned by jthill is the right approach. +1

It forces the file to be restored each time it is "added" to the index (meaning it never is actually added, since it hasn't changed).

Problem: How to force users to define it?

Solution: make them clone a template repo, which already contains:

• that empty file,
• and the .gitattributes file with the clean filter declared in it

If you set your main centralized repo to deny a ref update which is not a fast-forward one (git config receive.denyNonFastForwards true), your users won't have any choice but to push from a repo with the same common history than your template repo.
That means they will have those settings in place.

Sure they could delete said settings in a new commit, but that is when the pre-receive hooks from jthill's answer kicks in.
If they don't need to know about that files, chances are they won't mess with what was already defined for them.

Answer 2

It's easy to set up a repo to preserve a particular committed state for a file, and you can reject anything inbound you don't like.

To preserve a particular committed state for a file:

# do this once when the committed path/to/file is in the state you want
x=`git rev-parse master:path/to/file`
echo path/to/file filter=wired-to-$x >>.gitattributes

# then in each repo that wants it
git config filter.wired-to-$x.clean "git show $x"

The pre-receive hook tests inbound pushes, this simple one

#!/bin/sh
set -e
while read old new ref; do
        git ls-tree $new path/to/file \
        | awk '$3 != "e69de29bb2d1d6434b8b29ae775ad8c2e48c5391" {
                print "path/to/file is not empty"; exit 1; }'
done

will reject any push containing an inbound branch tip with a non-empty path/to/file. Sub in your "$x" to check for your desired state, and for added thoroughness you can run through all the inbounds with an inner rev-list loop feeding the ls-tree.

Answer 3

If they do not git add the changed file then it's not a problem. Teach them not to use git add . and it's near equivalents Difference of “git add -A” and “git add .”.

The project README could also include your git update-index --assume-unchanged instruction for the relevant file(s)

Answer 4

This seems like an application's task rather than git's. I would add this file to .gitignore and make sure that build process or any other process that uses it could create it.