RFC patchfor-each-ref: do not output empty lines

Hi,

This is a follow-up patch based on conversation from the thread: "[RFC PATCH 1/1] for-each-ref: add '--no-symbolic' option"

I had proposed a `--no-symbolic` option to git-for-each-ref that would filter out symbolic refs from the output. It was discovered that the behavior was already possible using an `%(if)` atom, but with the small caveat that empty lines would be output for each non-symbolic ref.

This patch changes the output behavior of git-for-each-ref such that it only prints lines for refs for which the format string expands to a non-empty string.

If this is deemed to be too disruptive of a change, a new command option could be added to opt in to the new behavior.

Cheers

Eric Freese (1):
  for-each-ref: do not output empty lines

 ref-filter.c            | 3 ++-
 t/t6300-for-each-ref.sh | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

If the format string expands to an empty string for a given ref, do not print the empty line.

This is helpful when wanting to print only certain kinds of refs that you can't already filter for.

For example, to exclude symbolic refs, use format string:
  "%(if)%(symref)%(then)%(else)%(refname)%(end)"

Or to include only symbolic refs, use:
  "%(if)%(symref)%(then)%(refname)%(end)"

Signed-off-by: Eric Freese <ericdfreese@gmail.com>
---
 ref-filter.c            | 3 ++-
 t/t6300-for-each-ref.sh | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

Eric Freese <ericdfreese@gmail.com> writes:

We tend to prefer stating the reason why we want to do so first and then give a command to the codebase to "become like so". Here is to illustrate how you would do it:

    The custom format specifier "--format=<format>" can be used to
    tell the for-each-ref command to say nothing for certain kind of
    refs, e.g.

       --format="%(if)%(symref)%(then)%(else)%(refname)%(end)"

    may be used to show the refname only for refs that are not
    symbolic refs.  Except that the command still would show one
    blank line per each symbolic ref, which is fairly useless.

    Introduce the `--omit-empty-lines` option to squelch these
    useless lines from the output.

While we are introducing a conditional, let's drop the useless fwrite of 0-byte while we are at it [*1*], i.e.

	if (final_buf.len && !omit_empty_lines) {
		fwrite(final_buf.buf, 1, final_buf.len, stdout);
		putchar('\n');
	}

Thanks.

[Footnote]

*1* "While we are at it", the existing code tempts me to drop fwrite
    and replace it with something along the lines of...

	printf("%*s\n", count, buf)

    but I refrained from doing so.  An enhancement patch like this
    is not a place to "improve" existing code (which should be done
    as a separate patch).

Junio C Hamano <gitster@pobox.com> writes:

Of course, that's a typo for "||"; if it is not empty, we'd emit no matter what, and if omit_empty is not given, we'd emit whether it is empty or not.

On Mon, Sep 09, 2019 at 11:02:07PM -0700, Junio C Hamano wrote:

Your proposed commit message (and the suggested code below) have a command-line option, but Eric's patch does it by default. Which do we want? :)

I'm inclined to say that this new behavior should be the default; even though it's technically a compatibility change, I find it hard to imagine people would see it as a regression.

But we could also introduce "--omit-empty-lines", and then flip the default. That gives an escape hatch of "--no-omit-empty-lines", at the minor cost of having to carry an option that we assume nobody would ever use.

-Peff