Re: [PATCH] subtree: fix argument handling in check_parents
- From
Johannes Schindelin <johannes.schindelin@gmx.de>
- Date
- Dec 3, 2021, 15:22 UTC
- Message-ID
- <nycvar.QRO.7.76.6.2112031610590.63@tvgsbejvaqbjf.bet>
- In-Reply-To
- <pull.1086.git.1638324413653.gitgitgadget@gmail.com>
Hi James,
On Wed, 1 Dec 2021, James Limbouris via GitGitGadget wrote:
Show 18 quoted lines
> From: James Limbouris <james@digitalmatter.com> > > 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 <james@digitalmatter.com> > --- > 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.
When I look through the commit history of `git-subtree.sh`, I see that the change was introduced in 315a84f9aa0 (subtree: use commits before rejoins for splits, 2018-09-28) (which was not really a coding style cleanup).
The change was actually not done right, if I read the commit correctly, because it added a new parameter _to the end_, even if the `check_parents()` function took an arbitrary number of parameters already. And indeed, it changed the `"$@"` into a "$1", pretending that only one parent would be passed.
Now, I do not really understand under what circumstances multiple parents could be passed to `check_parents()`, but I think that it does not matter whether you use `--format=%P` or `^@` (the former was changed to the latter in 19ad68d95d6 (subtree: performance improvement for finding unexpected parent commits, 2018-10-12)), you can always get an arbitrary number of parents that way.
The natural thing, now, would be to move the added `indent` parameter to the front of the parameter list, but I see that there was some cleanup in e9525a8a029 (subtree: have $indent actually affect indentation, 2021-04-27) which _removed_ that `indent` parameter.
So I _think_ your change is correct, even if I would love to see an easy-to-understand description of the scenario where more than one parents might be checked.
Another thing I would like to see is probably even more important: rather than using $*, we should use the original "$@" instead (with double-quotes). It should not matter a lot right now because we know that the parameters are the output of `git rev-parse "$rev^@"` (which provides them as a list of full object IDs, i.e. containing no white-space except to delimit the IDs), but it still the correct form to use "$@" instead.
Thanks, Dscho
Show 39 quoted lines
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1086%2Fjamesl-dm%2Fmaint-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1086/jamesl-dm/maint-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/1086
>
> contrib/subtree/git-subtree.sh | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> 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 $?
> local indent=$(($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
> --
> gitgitgadget
>