Re: [PATCH 2/2] fetch-pack: refactor writing promisor file

On Wed, Jan 13, 2021 at 08:25:40AM -0500, Jeff King wrote:

quoted

+void write_promisor_file(const char *promisor_name, struct ref **sought, int nr_sought)
+{
+	int i;
+	FILE *output = xfopen(promisor_name, "w");
+
+	for (i = 0; i < nr_sought; i++)
+		fprintf(output, "%s %s\n", oid_to_hex(&sought[i]->old_oid),
+			sought[i]->name);
+	fclose(output);
+}

We check errors on open via xfopen(), which is good. But we would not
notice any problems writing via fprintf or fclose. Is it worth doing
something like:

  err = ferror(output);
  err |= fclose(output);
  return err ? -1 : 0;

?

I agree below that *not* doing this isn't a regression against the
current code, since it doesn't check either, but this could be done
relatively easily. It is appropriate for both callers of
write_promisor_file() to immediately die() if they get an error, so I
think that this is potentially worth doing.

(As an aside, this ferror/fclose dance is awkward enough and has caused
us enough questions in the past that I wonder if it is worth
encapsulating into a wrapper).

From a quick grep through uses of ferror, there are a reasonable handful
of spots that I think could be improved if there was a ferror+fclose
helper, perhaps: xfclose().

The existing callers behave the same way (checking open, but not the
writes), so definitely not a regression. But the helper function may
provide an opportunity to make things more robust without adding a lot
of duplicated code.

Yep.

-Peff

Thanks,
Taylor