Subject: Re: [PATCH] patch-id: fix scan_hunk_header on diffs with -U1

From: Junio C Hamano <[email-masked]>
Date: Tue, 25 Jan 2022 21:13:25 -0800

Jerry Zhang <[email-masked]> writes:

> Normally diffs will contain a hunk header of the format
> "@@ -2,2 +2,15 @@ code". However when git diff is given "-U1"
> indicating that diffs are surrounded by only one line of
> context, it can omit the second comma separated value in
> either before or after line counts in the case where there
> is only one line.

Yes, it is possible that l and n in "@@ -k,l +m,n @@" is 1 in which
case ",1" is omitted altogether.  I however do not think it is
limited to "-U1".  The above description is inaccurate.

	$ echo one >foo
	$ git add foo
	$ echo two >foo
	$ git diff foo
	diff --git i/foo w/foo
	index 257cc5642c..5716ca5987 100644
	--- i/foo
	+++ w/foo
	@@ -1 +1 @@
	-one
	+two

> Fix by explicitly setting line count to 1 when there is
> no comma, and add a test.

It is correct to assume missing ,l and ,n as 1.  We should have the
same logic in apply.c (I wonder if there is a way to share the
parser, but I do not know if it is worth it).

> Signed-off-by: Jerry Zhang <[email-masked]>
> ---
>  builtin/patch-id.c  |  9 +++++++--
>  t/t4204-patch-id.sh | 32 +++++++++++++++++++++++++++++++-
>  2 files changed, 38 insertions(+), 3 deletions(-)
>
> diff --git a/builtin/patch-id.c b/builtin/patch-id.c
> index 822ffff51f..881fcf3273 100644
> --- a/builtin/patch-id.c
> +++ b/builtin/patch-id.c
> @@ -30,26 +30,31 @@ static int scan_hunk_header(const char *p, int *p_before, int *p_after)
>  
>  	q = p + 4;

I wonder if the repeated code from here ...

>  	n = strspn(q, digits);
>  	if (q[n] == ',') {
>  		q += n + 1;
> +		*p_before = atoi(q);
>  		n = strspn(q, digits);
> +	} else {
> +		*p_before = 1;
>  	}
> +

... down to here ought to be in a helper function to parse l out of
k[,l].  But that can and should be done as a post-fix cleanup.

>  	if (n == 0 || q[n] != ' ' || q[n+1] != '+')
>  		return 0;
>  
>  	r = q + n + 2;
>  	n = strspn(r, digits);
>  	if (r[n] == ',') {
>  		r += n + 1;
> +		*p_after = atoi(r);
>  		n = strspn(r, digits);
> +	} else {
> +		*p_after = 1;
>  	}
>  	if (n == 0)
>  		return 0;
>  
> -	*p_before = atoi(q);
> -	*p_after = atoi(r);
>  	return 1;
>  }
>  
>  static int get_one_patchid(struct object_id *next_oid, struct object_id *result,
>  			   struct strbuf *line_buf, int stable)
> diff --git a/t/t4204-patch-id.sh b/t/t4204-patch-id.sh
> index 80f4a65b28..08d10dfc3e 100755
> --- a/t/t4204-patch-id.sh
> +++ b/t/t4204-patch-id.sh
> @@ -36,11 +36,11 @@ test_expect_success 'patch-id output is well-formed' '
>  calc_patch_id () {
>  	patch_name="$1"
>  	shift
>  	git patch-id "$@" >patch-id.output &&
>  	sed "s/ .*//" patch-id.output >patch-id_"$patch_name" &&
> -	test_line_count -gt 0 patch-id_"$patch_name"
> +	test_line_count -eq 1 patch-id_"$patch_name"
>  }
>  
>  get_top_diff () {
>  	git log -p -1 "$@" -O bar-then-foo --
>  }
> @@ -200,6 +200,36 @@ EOF
>  test_expect_success 'patch-id handles no-nl-at-eof markers' '
>  	cat nonl | calc_patch_id nonl &&
>  	cat withnl | calc_patch_id withnl &&
>  	test_cmp patch-id_nonl patch-id_withnl
>  '
> +
> +cat >diffu1 <<\EOF
> +diff --git a/bar b/bar
> +index bdaf90f..31051f6 100644
> +--- a/bar
> ++++ b/bar
> +@@ -2 +2,2 @@
> + b
> ++c
> +diff --git a/car b/car
> +index 00750ed..2ae5e34 100644
> +--- a/car
> ++++ b/car
> +@@ -1 +1,2 @@
> + 3
> ++d
> +diff --git a/foo b/foo
> +index e439850..7146eb8 100644
> +--- a/foo
> ++++ b/foo
> +@@ -2 +2,2 @@
> + a
> ++e
> +EOF
> +
> +test_expect_success 'patch-id handles diffs with -U1' '
> +	cat diffu1 | calc_patch_id diffu1 &&
> +	test_config patchid.stable true &&
> +	cat diffu1 | calc_patch_id diffu1stable
> +'
>  test_done