From: Matthew Hughes <matthewhughes934@gmail.com>
Date: Fri, 29 May 2026 18:06:29 GMT
Subject: Re: Suggetsions for collaboration workflows in large repos
Message-ID: <ahnUeESE1x802Z9N@desktop>
In-Reply-To: <20260529163117.z2auhbg4sdxxgmis@archP14s>

On Fri, May 29, 2026 at 05:31:17PM +0100, Matthew Hughes wrote:
> I thought about doing something like tracking
> `refs/heads*/some-colleague-branch` from the remote, since with the wildcard
> `*` I at least won't the fatal error on the missing reference during fetch, but
> that risks my config containing an ever growing list of such wildcards, or a
> bunch of manual work occasionally cleaning up old ones (or maybe that could be
> automated).

I hacked some scripts to automate this. Firstly, one for fetching:

1. Fetches the branch
2. Adds a fetch config with wildcard hacks so `git fetch` brings in updates for
  that branch (the refspec should match _exactly_ that branch and never
  anything more)
3. Adds a separate ref to record that we're tracking this branch (so something
  knows to clean it up later)

    #!/usr/bin/env bash

    set -o errexit -o pipefail -o nounset

    # save command as e.g. git-fetch-other
    CMD_NAME="$(basename "$0" | sed 's/git-//g')"
    if [ $# -lt 1 ]
    then
        echo "usage: git $CMD_NAME branch-name [ remote-name ]" >&2
        exit 1
    fi

    BRANCH_NAME="$1"
    REMOTE_NAME="${2:-origin}"
    FETCH_CONFIG_NAME="remote.$REMOTE_NAME.fetch"

    git fetch "$REMOTE_NAME" "$BRANCH_NAME"
    git checkout -b "$BRANCH_NAME"

    # we want to record that we are tracking this branch, to do this create
    # a new ref whose name tells us what we're tracking, but whose value is
    # unimportant. So as a placeholder value just use the hash of an empty tree
    # taken from https://git.kernel.org/pub/scm/git/git.git/commit/?id=9c8a294a1ae1335511475db9c0eb8841c0ec9738
    EMPTY_TREE_REF="$(git hash-object -t tree /dev/null)"

    # refspec used to track the branch: we expect branches to be deleted from the
    # upstream when merged so tracking exactly:
    # "+refs/heads/$BRANCH_NAME:refs/remotes/$REMOTE_NAME/$BRANCH_NAME" will error
    # when we go to fetch that exact ref after its removed upstream.
    # so HACK around this: add wildcards that we still expect to only ever match
    # this exact branch (but doesn't have the issue of git complaining when it
    # tries to fetch an _exact_ ref)
    TRACKING_REFSPEC="+refs/heads*/$BRANCH_NAME:refs/remotes*/$REMOTE_NAME/$BRANCH_NAME"

    # record that we're tracking this branch. First check we've not already
    # recorded this, then ...
    if ! git config get --local --fixed-value --value "$TRACKING_REFSPEC" "$FETCH_CONFIG_NAME" >/dev/null
    then
        # ... set the config to track it for fetching, and ...
        git config set --comment "$CMD_NAME: tracking at $(date -I)"  --local --append "$FETCH_CONFIG_NAME" "$TRACKING_REFSPEC"
        # ... record that we have special cased this tracking
        git update-ref "refs/tracked/$REMOTE_NAME/$BRANCH_NAME" "$EMPTY_TREE_REF"
    fi

And the cleanup script (needs to be run periodically):

1. Collects all the remote branches we know about
2. Checks all the references from step 3. above and checks if any branches
defined there are missing remotes (I have fetch.prune=true to keep the remote
tracking references up-to-date)
3. If they are, drops the tracking config for that branch

    #!/usr/bin/env bash

    set -o errexit -o pipefail -o nounset

    REMOTE_NAME="${1:-origin}"
    TRACKED_REF_PREFIX="refs/tracked/$REMOTE_NAME"
    REMOTE_REF_PREFIX="refs/remotes/$REMOTE_NAME"

    declare -A remote_branch_lookup
    while read -r remote_ref
    do
        # strip prefix, e.g. 'refs/remotes/origin/some-branch' -> 'some-branch'
        branch_name="${remote_ref#$REMOTE_REF_PREFIX/}"
        remote_branch_lookup["$branch_name"]=1
    done < <(git for-each-ref --format='%(refname)' "$REMOTE_REF_PREFIX/")

    while read -r tracking_info
    do
        tracked_branch="${tracking_info#$TRACKED_REF_PREFIX/}"
        if ! [[ -v "remote_branch_lookup[$tracked_branch]" ]]
        then
            echo "branch $tracked_branch has been removed from the remote, untracking it"
            git update-ref -d "$TRACKED_REF_PREFIX/$tracked_branch"

            tracking_refspec="+refs/heads*/$tracked_branch:refs/remotes*/$REMOTE_NAME/$tracked_branch"
            git config unset --local --fixed-value --value "$tracking_refspec" "remote.$REMOTE_NAME.fetch"
        fi
    done < <(git for-each-ref --format='%(refname)' "$TRACKED_REF_PREFIX/")

So functionally I think this allows for the workflow I want, but does feel like
a big ol' hack :>