Re: [PATCH RFC] diff: add SUBMODULE_DIFF format to display submodule diff

Jacob Keller [off-list ref] 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?