Re: RFC: Using '--no-output-indicator-old' to only show new state

[Linus Torvalds <torvalds@linux-foundation.org>]

[-- Attachment #1: Type: text/plain, Size: 981 bytes --]

On Thu, Mar 10, 2022 at 1:26 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> I often use -W and the above would give us a natural extension, but
> I agree that is a bit too dense and totally unintuitive.  As we use
> parse-options for patch output formatting options, my pick would be
> "--new-only" vs "--old-only" (

I was "ok, that's really easy" and did

+               OPT_ALIAS(0, "new-only", "no-output-indicator-old"),
+               OPT_ALIAS(0, "old-only", "no-output-indicator-new"),

but sadly the parse-options alias code isn't quite smart enough.

Doing it with an explicit callback obviously works, but the "unique
abbreviations" part doesn't actually work for me. I think it's due to
PARSE_OPT_KEEP_UNKNOWN making the abbreviated options not work, but I
don't know tha option parsing code well enough.

Here's the stupid patch that "works" but doesn't allow the shortened
version. Maybe somebody can point out what silly thing I did wrong.

               Linus

[-- Attachment #2: patch.diff --]
[-- Type: text/x-patch, Size: 1321 bytes --]

 diff.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/diff.c b/diff.c
index 895951b849..cf168e727d 100644
--- a/diff.c
+++ b/diff.c
@@ -5000,6 +5000,17 @@ static int diff_opt_char(const struct option *opt,
 	return 0;
 }
 
+static int diff_opt_no_char(const struct option *opt,
+			 const char *arg, int unset)
+{
+	char *value = opt->value;
+
+	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
+	*value = 0;
+	return 0;
+}
+
 static int diff_opt_color_moved(const struct option *opt,
 				const char *arg, int unset)
 {
@@ -5493,6 +5504,14 @@ static void prep_parse_options(struct diff_options *options)
 			       N_("<char>"),
 			       N_("specify the character to indicate a context instead of ' '"),
 			       PARSE_OPT_NONEG, diff_opt_char),
+		OPT_CALLBACK_F(0, "new-only",
+			       &options->output_indicators[OUTPUT_INDICATOR_OLD], NULL,
+			       N_("show only new lines in diff"),
+			       PARSE_OPT_NONEG | PARSE_OPT_NOARG, diff_opt_no_char),
+		OPT_CALLBACK_F(0, "old-only",
+			       &options->output_indicators[OUTPUT_INDICATOR_NEW], NULL,
+			       N_("show only old lines in diff"),
+			       PARSE_OPT_NONEG | PARSE_OPT_NOARG, diff_opt_no_char),
 
 		OPT_GROUP(N_("Diff rename options")),
 		OPT_CALLBACK_F('B', "break-rewrites", &options->break_opt, N_("<n>[/<m>]"),