From: Junio C Hamano <gitster@pobox.com>
Date: Fri, 14 Sep 2018 16:59:24 GMT
Subject: Re: [PATCH v1 2/4] fsmonitor: update GIT_TEST_FSMONITOR support
Message-ID: <xmqqmuskc8wj.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20180914143708.63024-3-benpeart@microsoft.com>

Ben Peart <benpeart@microsoft.com> writes:

> +if test -n "$GIT_FSMONITOR_TEST"
> +then
> +	if test -n "$GIT_TEST_FSMONITOR"
> +	then
> +		echo "warning: the GIT_FSMONITOR_TEST variable has been renamed to GIT_TEST_FSMONITOR"
> +	else
> +		echo "error: the GIT_FSMONITOR_TEST variable has been renamed to GIT_TEST_FSMONITOR"
> +		exit 1
> +	fi
> +fi

I would have expected that, because we are now doing multiple pairs
of variables in a single series, we would add a helper function that
can be called like so:

	check_var_migration GIT_FSMONITOR_TEST GIT_TEST_FSMONITOR

in the earliest step.  Perhaps something like this.

check_var_migration () {
	old_name=$1 new_name=$2
	eval "old_isset=\${${old_name}:+isset}"
	eval "new_isset=\${${new_name}:+isset}"
	case "$old_isset,$new_isset" in
	isset,)
		echo >&2 "error: $old_name is now $new_name"
		exit 1 ;;
	isset,isset)
		# enable this, once $old_name no longer is valid anywhere
		# echo >&2 "warning: $old_name is now $new_name"
		# echo >&2 "hint: remove $old_name"
		;;
	esac
}