From: Junio C Hamano <gitster@pobox.com>
Date: Tue, 09 Aug 2016 22:40:29 GMT
Subject: Re: [PATCH RFC] diff: add SUBMODULE_DIFF format to display submodule diff
Message-ID: <xmqq37md8t2a.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20160809223219.17982-1-jacob.e.keller@intel.com>

Jacob Keller <jacob.e.keller@intel.com> writes:

> +static int prepare_submodule_diff(struct strbuf *buf, const char *path,
> +		unsigned char one[20], unsigned char two[20])
> +{
> +	struct child_process cp = CHILD_PROCESS_INIT;
> +	cp.git_cmd = 1;
> +	cp.dir = path;
> +	cp.out = -1;
> +	cp.no_stdin = 1;
> +	argv_array_push(&cp.args, "diff");
> +	argv_array_push(&cp.args, sha1_to_hex(one));
> +	argv_array_push(&cp.args, sha1_to_hex(two));
> +
> +	if (start_command(&cp))
> +		return -1;
> +
> +	if (strbuf_read(buf, cp.out, 0) < 0)
> +		return -1;
> +
> +	if (finish_command(&cp))
> +		return -1;
> +
> +	return 0;
> +}

It is a good idea to keep the submodule data isolated from the main
process by going through run-command/start-command interface (I
think the call to add_submodule_odb() should be rethought and
removed if possible).

I however wonder if you want to use src/dst-prefix to make the path
to the submodule appear there?  That is, if your superproject has a
submodule at "dir/" and two versions of the submodule changes a file
"doc/README", wouldn't you rather want to see

	diff --git a/dir/doc/README b/dir/doc/README

instead of comparison between a/doc/README and b/doc/README?