Re: [PATCH v3 4/4] log: speed up --follow following renames for non-linear history

[Patrick Steinhardt <ps@pks.im>]

On Thu, Oct 22, 2026 at 10:47:06PM +0200, Miklos Vajna wrote:
> diff --git a/log-tree.c b/log-tree.c
> index c5ac6c2bcb..d5ce58d91d 100644
> --- a/log-tree.c
> +++ b/log-tree.c
> @@ -1153,6 +1169,29 @@ void release_follow_pathspec_slab(struct rev_info *opt)
>  	FREE_AND_NULL(opt->follow_pathspec_slab);
>  }
>  
> +/*
> + * When the path in a merge is the same as in 'same', does the path still need
> + * renames to be followed in 'parent'? Only if the merge has the path, 'parent'
> + * doesn't have it, but its fork point with 'same' had it, e.g. 'parent'
> + * renamed the path.
> + */
> +static int follow_needs_renames(struct rev_info *opt, struct commit *parent,
> +				struct commit *same, const char *path)
> +{
> +	struct commit_list *bases = NULL, *base;
> +	int ret = 0;
> +
> +	if (commit_has_path(opt, parent, path) ||
> +	    !commit_has_path(opt, same, path))
> +		return 0;

Doesn't this miss the reverse case where we have the path in "parent",
but not in "same"? So basically this test case, which is very similar to
the one you already added to 4219:

test_expect_success 'setup merge keeping the renamed path, other side edited the old one' '
	git init keep-renamed &&
	printf "line 1\nline 2\nline 3\nline 4\nline 5\n" >keep-renamed/F &&
	git -C keep-renamed add F &&
	test_tick &&
	git -C keep-renamed commit -m "O: add F" &&
	git -C keep-renamed branch B &&
	git -C keep-renamed mv F G &&
	test_tick &&
	git -C keep-renamed commit -m "A1: rename F to G on master" &&

	git -C keep-renamed checkout B &&
	printf "line 1\nline 2\nline 3\nline 4 T\nline 5\n" >keep-renamed/F &&
	test_tick &&
	git -C keep-renamed commit -am "B2: update F on B" &&

	git -C keep-renamed checkout master &&
	test_tick &&
	git -C keep-renamed merge -s ours -m "M: merge B, keep G, drop F" B
'

test_expect_success '--follow follows an edit on the side the merge did not take' '
	git -C keep-renamed log --follow --pretty=tformat:%s G >actual &&
	cat >expect <<-\EOF &&
	B2: update F on B
	A1: rename F to G on master
	O: add F
	EOF
	test_cmp expect actual
'

That test passes with HEAD~, but fails with HEAD.

Patrick