Subject: Re: [PATCH] blame: fix unblamable and ignored lines in porcelain mode

From: Patrick Steinhardt <[email-masked]>
Date: Mon, 24 Mar 2025 11:16:31 +0100

On Sun, Mar 23, 2025 at 08:58:03AM -0700, Junio C Hamano wrote:
> Karthik Nayak <[email-masked]> writes:
> 
> > However, this option was never extended to the porcelain mode of
> > 'git-blame(1)'. Since the documentation does not indicate this
> > exclusion, it is a bug.
> 
> I agree it is a bug when people added ignore or unblamable support
> that they did not _consider_ what to do with their new pieces of
> information to help porcelain writers.  It is not a bug in the code
> per-se, but it is a bug in the brain of these people ;-)
> 
> But prefixing random garbage to the commit object name line in the
> porcelain mode output does not sound like the right solution to the
> bug, either.
> 
> When enhancing an existing output format, make sure that your
> changes will have minimum empact to existing parsers that do not
> know about your extension.  It is reasonably expected that existing
> Porcelain scripts reading from --porcelain mode output works by
> 
>  - Recognizing a line that match "^[0-9a-f]{40} \d+ \d+ \d+$" and
>    take it as the beginning of a new record;
> 
>  - Collect all info lines before the payload line.  Lines that
>    describe per-commit information are not repeated if it is already
>    shown, so remember them when you see the commit for the first
>    time, and recall them when you recognize the commit you already
>    saw.
> 
>  - A payload line is indented with HT and terminates the record.
> 
> If you start to add unrecognizable garbage to the line with very
> well known fixed format that is used as record delimiter, you would
> break the existing parsers, which is not a very nice thing to do.
> Are there other and better ways you can think of to add new pieces
> of information like this in a way with less severe damage?

I think the porcelain mode is already built so that it can be extended
with arbitrary new information, no? In `emit_one_suspect_detail()` we
end up printing one line per info we want to display. I would have
expected that we can extend that function to also print information
around unblamable or ignored commits, like we already do for boundary
commits. E.g. something like the patch further down.

Thanks!

Patrick

diff --git a/builtin/blame.c b/builtin/blame.c
index c470654c7ec..cd8322e2619 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -255,7 +255,8 @@ static void write_filename_info(struct blame_origin *suspect)
  * the first time each commit appears in the output (unless the
  * user has specifically asked for us to repeat).
  */
-static int emit_one_suspect_detail(struct blame_origin *suspect, int repeat)
+static int emit_one_suspect_detail(struct blame_entry *ent,
+				   struct blame_origin *suspect, int repeat)
 {
 	struct commit_info ci = COMMIT_INFO_INIT;
 
@@ -275,6 +276,10 @@ static int emit_one_suspect_detail(struct blame_origin *suspect, int repeat)
 	printf("summary %s\n", ci.summary.buf);
 	if (suspect->commit->object.flags & UNINTERESTING)
 		printf("boundary\n");
+	if (mark_unblamable_lines && ent->unblamable)
+		printf("unblamable\n");
+	if (mark_ignored_lines && ent->ignored)
+		printf("ignored\n");
 
 	commit_info_destroy(&ci);
 
@@ -295,7 +300,7 @@ static void found_guilty_entry(struct blame_entry *ent, void *data)
 		printf("%s %d %d %d\n",
 		       oid_to_hex(&suspect->commit->object.oid),
 		       ent->s_lno + 1, ent->lno + 1, ent->num_lines);
-		emit_one_suspect_detail(suspect, 0);
+		emit_one_suspect_detail(ent, suspect, 0);
 		write_filename_info(suspect);
 		maybe_flush_or_die(stdout, "stdout");
 	}
@@ -344,9 +349,10 @@ static const char *format_time(timestamp_t time, const char *tz_str,
 #define OUTPUT_COLOR_LINE           (1U<<10)
 #define OUTPUT_SHOW_AGE_WITH_COLOR  (1U<<11)
 
-static void emit_porcelain_details(struct blame_origin *suspect, int repeat)
+static void emit_porcelain_details(struct blame_entry *ent,
+				   struct blame_origin *suspect, int repeat)
 {
-	if (emit_one_suspect_detail(suspect, repeat) ||
+	if (emit_one_suspect_detail(ent, suspect, repeat) ||
 	    (suspect->commit->object.flags & MORE_THAN_ONE_PATH))
 		write_filename_info(suspect);
 }
@@ -366,7 +372,7 @@ static void emit_porcelain(struct blame_scoreboard *sb, struct blame_entry *ent,
 	       ent->s_lno + 1,
 	       ent->lno + 1,
 	       ent->num_lines);
-	emit_porcelain_details(suspect, repeat);
+	emit_porcelain_details(ent, suspect, repeat);
 
 	cp = blame_nth_line(sb, ent->lno);
 	for (cnt = 0; cnt < ent->num_lines; cnt++) {
@@ -376,7 +382,7 @@ static void emit_porcelain(struct blame_scoreboard *sb, struct blame_entry *ent,
 			       ent->s_lno + 1 + cnt,
 			       ent->lno + 1 + cnt);
 			if (repeat)
-				emit_porcelain_details(suspect, 1);
+				emit_porcelain_details(ent, suspect, 1);
 		}
 		putchar('\t');
 		do {