Subject: Re: [PATCH] subtree: fix argument handling in check_parents

From: Junio C Hamano <[email-masked]>
Date: Wed, 01 Dec 2021 15:04:51 -0800

"James Limbouris via GitGitGadget" <[email-masked]> writes:

> From: James Limbouris <[email-masked]>
>
> check_parents was taking all of its arguments as a single string,
> and erroneously passing them to cache_miss as a single string.
> cache_miss would then fail, and the spurious cache misses it produced
> would hurt performance.
>
> For consistency, take multiple arguments in check_parents,
> and pass all of them to cache_miss separately.
>
> Signed-off-by: James Limbouris <[email-masked]>
> ---
>     subtree: fix argument handling in check_parents
>     
>     Hello git developers. Please consider this small patch that fixes a bug
>     introduced during a coding style cleanup of the subtree command. Changes
>     to the argument handling were causing check_parents to fail when more
>     than one parent was supplied, which led to a small loss of performance.

I do not do "git subtree", and this cannot really be a proper review
that is more than "Looks OK from a cursory look", but anyway...

It seems that 315a84f9 (subtree: use commits before rejoins for
splits, 2018-09-28) is what broke the logic, but it does not look
like a coding style clean-up to me.

> diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
> index 7f767b5c38f..56f24000c2c 100755
> --- a/contrib/subtree/git-subtree.sh
> +++ b/contrib/subtree/git-subtree.sh
> @@ -296,10 +296,9 @@ cache_miss () {
>  	done
>  }
>  
> -# Usage: check_parents PARENTS_EXPR
> +# Usage: check_parents [REVS...]
>  check_parents () {
> -	assert test $# = 1
> -	missed=$(cache_miss "$1") || exit $?
> +	missed=$(cache_miss $*) || exit $?

We know at this point each of $1, $2, etc. have exactly one
revision, and we want cache_miss function to take one revision per
its parameter, so writing "$@" is much more preferrable over $* even
though they do the same thing in practice in the context of this
code, I think.

>  	local indent=$(($indent + 1))
>  	for miss in $missed
>  	do
> @@ -753,7 +752,7 @@ process_split_commit () {
>  	fi
>  	createcount=$(($createcount + 1))
>  	debug "parents: $parents"
> -	check_parents "$parents"
> +	check_parents $parents
>  	newparents=$(cache_get $parents) || exit $?
>  	debug "newparents: $newparents"
>  
>
> base-commit: e9d7761bb94f20acc98824275e317fa82436c25d