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Add git sync, and stop trusting the cached default branch

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BuildEmpire/Totara renamed its default branch from main to totara-20.
Nothing local noticed, because refs/remotes/origin/HEAD is written once at
clone time and remote.<name>.followRemoteHEAD defaults to `create`, which
only fills the ref in when it is missing. So `git default-branch` still
said main, as did nvim's diff-against-branch prompt.

bin/git-sync does the start-of-work sequence for a fork - fast-forward the
default branch from upstream, push it to origin - and works out which
branch that is by asking the server, not the cache. It sets the cached
HEADs from the answer, so everything reading that ref agrees afterwards.
It lives in bin/ rather than as an alias because git picks up git-<name>
on the $PATH as a subcommand, and this is more shell than a gitconfig
alias should hold. followRemoteHEAD = always is set for origin as well, so
an ordinary fetch keeps the ref current without running the script.

The nvim prompt now prefers origin, then upstream, then the remaining
remotes. It took the first remote alphabetically before, which in
be-edition means kdog - a colleague's fork - rather than anything
authoritative.

Verified against a fixture of bare repos whose default branch is
totara-20 and whose cached HEAD is stale: the branch is created tracking
origin when absent, fast-forwarded when behind, pushed to the fork,
refuses to merge when the local copy has diverged, and is a no-op on a
second run. The nvim prompt was checked in three real repos.
This commit is contained in:
Jonny Barnes 2026-08-27 16:05:49 +01:00
commit 80683b82c1
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4 changed files with 137 additions and 11 deletions
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16
gitconfig
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@ -2,13 +2,18 @@
# list aliases
aliases = !git config --get-regexp 'alias.*' | colrm 1 6 | sed 's/[ ]/ = /' | sort
bdm = "!git branch --merged | grep -v '*' | xargs -n 1 git branch -d"
default-branch = "!git symbolic-ref refs/remotes/origin/HEAD | cut -d'/' -f4"
# Reads origin's cached HEAD, which `git sync` and remote.origin.followRemoteHEAD
# below keep pointing at whatever the server currently calls its default.
# --short over cut -d/ -f4, which mangles names like release/1.0.
default-branch = "!git symbolic-ref --short refs/remotes/origin/HEAD | sed 's|^origin/||'"
lg = log --graph --pretty=tformat:'%Cred%h%Creset -%C(auto)%d%Creset %s %Cgreen(%an %ar)%Creset'
lg2 = log --graph --abbrev-commit --decorate --format=format:'%C(bold blue)%h%C(reset) - %C(bold cyan)%aD%C(reset) %C(bold green)(%ar)%C(reset)%C(bold yellow)%d%C(reset)%n' %C(white)%s%C(reset) %C(dim white)- %an%C(reset)' --all
lastchange = log -p --follow -n 1
plog = log --graph --pretty='format:%C(red)%d%C(reset) %C(yellow)%h%C(reset) %ar %C(green)%aN%C(reset) %s'
rank = shortlog -sn --no-merges
st = status -sb
# `git sync` is not here - it is bin/git-sync, on the $PATH, which git picks
# up as a subcommand. `git aliases` above will not list it.
tlog = log --stat --since='1 Day Ago' --graph --pretty=oneline --abbrev-commit --date=relative
[apply]
@ -35,6 +40,15 @@
[pull]
ff = only
[remote "origin"]
# refs/remotes/origin/HEAD is written once at clone time, and the default
# `create` only fills it in when missing - so a default branch renamed on the
# server (main -> totara-20) leaves every tool reading that ref pointing at a
# branch that may not even exist. `always` re-points it on each fetch, off the
# ref advertisement that fetch already receives, so it costs no extra round
# trip. Only applies to remotes actually named origin.
followRemoteHEAD = always
[core]
pager = delta --side-by-side --width ${FZF_PREVIEW_COLUMNS-$COLUMNS}