log-tree: show_log: make commentary block delimiting reusable

In patches generated by git-format-patch, the area below the "---" line
following the commit message and before the actual 'diff' can be used
for commentary which the patch author wants to convey to readers of the
patch itself but not include in the commit message proper.

By default, the commentary area is empty, however, the --notes option
causes it to be populated with notes associated with the commit. In the
future, other options may be added which also insert content into the
commentary section.

To accommodate this, factor out the logic which delimits commentary
blocks from the commit message so that it can be re-used for upcoming
optional inserted content.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

log-tree.c

@@ -541,6 +541,16 @@ static int show_mergetag(struct rev_info *opt, struct commit *commit)
 	return for_each_mergetag(show_one_mergetag, commit, opt);
 }
 
+static void next_commentary_block(struct rev_info *opt, struct strbuf *sb)
+{
+	const char *x = opt->shown_dashes ? "\n" : "---\n";
+	if (sb)
+		strbuf_addstr(sb, x);
+	else
+		fputs(x, opt->diffopt.file);
+	opt->shown_dashes = 1;
+}
+
 void show_log(struct rev_info *opt)
 {
 	struct strbuf msgbuf = STRBUF_INIT;
@@ -698,10 +708,8 @@ void show_log(struct rev_info *opt)
 
 	if ((ctx.fmt != CMIT_FMT_USERFORMAT) &&
 	    ctx.notes_message && *ctx.notes_message) {
-		if (cmit_fmt_is_mail(ctx.fmt)) {
-			strbuf_addstr(&msgbuf, "---\n");
-			opt->shown_dashes = 1;
-		}
+		if (cmit_fmt_is_mail(ctx.fmt))
+			next_commentary_block(opt, &msgbuf);
 		strbuf_addstr(&msgbuf, ctx.notes_message);
 	}
 
@@ -765,9 +773,10 @@ int log_tree_diff_flush(struct rev_info *opt)
 
 			/*
 			 * We may have shown three-dashes line early
-			 * between notes and the log message, in which
-			 * case we only want a blank line after the
-			 * notes without (an extra) three-dashes line.
+			 * between generated commentary (notes, etc.)
+			 * and the log message, in which case we only
+			 * want a blank line after the commentary
+			 * without (an extra) three-dashes line.
 			 * Otherwise, we show the three-dashes line if
 			 * we are showing the patch with diffstat, but
 			 * in that case, there is no extra blank line