Subject: Re: [PATCH] diff: disabled quick optimization with --find-copies-harder

From: Phillip Wood <[email-masked]>
Date: Sun, 9 Nov 2025 14:18:39 +0000

On 09/11/2025 12:11, René Scharfe wrote:
> If --find-copies-harder is given, diff-lib.c::show_modified() queues
> even non-modified entries using diff_change() because we need them for
> copy detection.  diff_change() sets flags.has_changes, though.  If
> --quiet is also given this causes diff_can_quit_early() to declare we're
> done after seeing only the very first entry, which is way too soon.
> Disable this optimization in that case.

Stepping back a bit I'm confused as to why we don't disable rename and 
copy detection when "--quiet" is given. I can't see why detecting copies 
or renames would change the exit code but maybe I'm missing something.

Thanks

Phillip

> This issue is hidden without --no-ext-diff because then we set
> flags.diff_from_contents, which disables the optimization in a
> different way.
> 
> Reported-by: D. Ben Knoble <[email-masked]>
> Signed-off-by: René Scharfe <[email-masked]>
> ---
>   diff.c              |  1 +
>   t/t4007-rename-3.sh | 10 ++++++++++
>   2 files changed, 11 insertions(+)
> 
> diff --git a/diff.c b/diff.c
> index a1961526c0..84ac148c37 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -7188,6 +7188,7 @@ int diff_can_quit_early(struct diff_options *opt)
>   {
>   	return (opt->flags.quick &&
>   		!opt->filter &&
> +		!opt->flags.find_copies_harder &&
>   		opt->flags.has_changes);
>   }
>   
> diff --git a/t/t4007-rename-3.sh b/t/t4007-rename-3.sh
> index e8faf0dd2e..3fc81bcd76 100755
> --- a/t/t4007-rename-3.sh
> +++ b/t/t4007-rename-3.sh
> @@ -41,6 +41,16 @@ test_expect_success 'copy detection, cached' '
>   	compare_diff_raw current expected
>   '
>   
> +test_expect_success 'exit code of quiet copy detection' '
> +	test_expect_code 1 \
> +	git diff --quiet --cached --find-copies-harder $tree
> +'
> +
> +test_expect_success 'exit code of quiet copy detection with --no-ext-diff' '
> +	test_expect_code 1 \
> +	git diff --quiet --cached --find-copies-harder --no-ext-diff $tree
> +'
> +
>   # In the tree, there is only path0/COPYING.  In the cache, path0 and
>   # path1 both have COPYING and the latter is a copy of path0/COPYING.
>   # However when we say we care only about path1, we should just see