Subject: Re: [GSoC PATCH v2] apply: report the location of corrupt patches

From: Junio C Hamano <[email-masked]>
Date: Mon, 16 Mar 2026 11:19:11 -0700

Jialong Wang <[email-masked]> writes:

> When parsing a corrupt patch, git apply reports only the line number.
> That does not tell the user which input the line number refers to.
>
> Include the patch input path in the error message, and reset the line
> number for each patch input so the reported location remains useful
> when multiple patch files are provided.
>
> Add tests for file input, standard input, and multiple patch inputs.
>
> Signed-off-by: Jialong Wang <[email-masked]>
> ---
> Changes since v1:
> - reset the line number for each patch input
> - add a test for multiple patch inputs where one input is corrupted
>
>  apply.c               |  4 +++-
>  t/t4100-apply-stat.sh | 38 +++++++++++++++++++++++++++++++++++++-
>  2 files changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/apply.c b/apply.c
> index b6dd1066a0..b7b0a201b3 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -1875,7 +1875,8 @@ static int parse_single_patch(struct apply_state *state,
>  		len = parse_fragment(state, line, size, patch, fragment);
>  		if (len <= 0) {
>  			free(fragment);
> -			return error(_("corrupt patch at line %d"), state->linenr);
> +			return error(_("corrupt patch at %s:%d"),
> +				     state->patch_input_file, state->linenr);
>  		}
>  		fragment->patch = line;
>  		fragment->size = len;
> @@ -4825,6 +4826,7 @@ static int apply_patch(struct apply_state *state,
>  	int flush_attributes = 0;
>  
>  	state->patch_input_file = filename;
> +	state->linenr = 1;
>  	if (read_patch_file(&buf, fd) < 0)
>  		return -128;
>  	offset = 0;

This change is expecially interesting; it shows that practically
nobody feeds more than one patch to a single invocation of the
command ("git am" certainly does not) that this has gone undetected
ever since it was written by Linus 46979f56 (git-apply: improve
error detection and messages, 2005-05-23) ;-)

And all the changes contained in this patch look correctly done.

Having said that, there are places in apply.c that still report
errors only the line number, which we may want to address with a
follow-up patch, or in an updated version of this patch.
find_header() is one, parse_git_diff_header() is another.  There
might be more.

Thanks, will queue.