Re: [PATCH 4/8] perf/run: use $default_value instead of $4

From: Junio C Hamano <gitster@pobox.com>
Date: Dec 13, 2017, 20:40 UTC
Message-ID: <xmqqbmj2wedd.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20171213151344.2138-5-chriscool@tuxfamily.org>

Christian Couder <christian.couder@gmail.com> writes:

Show 24 quoted lines

> Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
> ---
>  t/perf/run | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/t/perf/run b/t/perf/run
> index 43e4de49ef..bbd703dc4f 100755
> --- a/t/perf/run
> +++ b/t/perf/run
> @@ -105,7 +105,7 @@ get_var_from_env_or_config () {
>  	env_var="$1"
>  	conf_sec="$2"
>  	conf_var="$3"
> -	# $4 can be set to a default value
> +	default_value="$4" # optional
>  
>  	# Do nothing if the env variable is already set
>  	eval "test -z \"\${$env_var+x}\"" || return
> @@ -123,7 +123,7 @@ get_var_from_env_or_config () {
>  	conf_value=$(git config -f "$GIT_PERF_CONFIG_FILE" "$var") &&
>  	eval "$env_var=\"$conf_value\"" && return
>  
> -	test -n "${4+x}" && eval "$env_var=\"$4\""
> +	test -n "${default_value+x}" && eval "$env_var=\"$default_value\""

This conversion changes the behaviour. Because default_value is always set by your change in the previous hunk, we end up always doing this eval.

The original says "If $4 is set, then ${4+x} becomes x and if $4 is not set, ${4+x} is empty, so let's check if ${4+x} is a non-empty string to see if $4 is set. If ${4+x} is a non-empty string, that means $4 was set so we do the eval.

If you want to be able to use this helper to specify a default value of an empty string (which the orignal that used $4 did), then the previous hunk must be corrected so that it does not unconditionally set default_value to $4. Perhaps like

	if test -n "${4+x}"
	then
		default_value=$4
	else
		unset default_value || :
	fi

or something.

>  }
>  
>  run_subsection () {