safe git rebase (pre-rebase hook)

_safe rebase.md

Description

This gist contains a script of mine that prevents unsafe rebases.

I consider a rebase as unsafe if there is work based on the branch to rebase.

This works should work cross platform as long as bash is installed correctly on /bin/bash (git for windows comes with bash).

This hook can be useful if git is configured to do a rebase instead of a merge when pulling.

How to use

The script (the pre-rebase file) needs to be in the hooks directory of the local git repository (the .git directory) you want to work it in.

If you want the script to be added to the hooks directory automatically, you can create a template directory for git repositories.

To do that, you just need to create a directory with a subdirectory hooks. After that, set the init.templatedir config to that directory (git config --global init.templatedir <your template directory>) and copy the script (the pre-rebase file) to the directory.

pre-rebase

#!/bin/bash
function printDelim(){
	echo "====================================================================================================="
}
function debug(){
	if [[ -n "$DEBUG" ]]; then
		echo -e "[DEBUG] \e[90m$*\e[0m"
	fi
}
function info(){
	echo -e "\e[94m$*\e[0m"
}
function err(){
	echo -e "\e[91m$*\e[0m"
}
function success(){
	echo -e "\e[92m$*\e[0m"
}
if [[ -n "$SKIP_REBASE_CHECK" ]] && [[ "$SKIP_REBASE_CHECK" != "0" ]]; then
	info "rebase check skipped because SKIP_REBASE_CHECK is set (and not 0)"
	exit 0
fi


from="$1"
to="$2"
if [[ -z "$to" ]]; then
	to="HEAD"
fi
printDelim
info "trying to rebase $to from $from"
info "testing if there is work that is based of newer commits"
printDelim
base="$(git merge-base "$from" "$to")"
debug "base: $base"
for branch in $(git for-each-ref --format='%(refname)'); do
	if [[ "$branch" == \** ]]; then
		debug "skip $branch because of asterisk"
	elif [[ "$(git rev-parse "$branch")" != "$(git rev-parse "$to")" ]]; then
		debug "testing branch: $branch"
		common="$(git merge-base "$branch" "$to")"
		if [[ -z "$common" ]]; then
			debug "skip $branch because no common ancestor has been found"
		elif [[ -z "$(git log "$base".."$common")" ]]; then
			debug "branch $branch ok"
		else
			debug "Problems with branch $branch" > /dev/stderr
			printDelim
			err "\"$branch\" contains work that is based on work that would be rebased."
			err "It is possibly unsafe to continue this rebase."
			err "Try to fix those problems or run this command again using with the variable \"SKIP_REBASE_CHECK\" set to non-zero if you still want to rebase."
			printDelim
			exit 255
		fi
	else
		debug "skipping $branch $branch as it is the branch to rebase"
	fi
done
printDelim
success "This rebase seems safe."
printDelim
exit 0