format-patch: move range/inter diff at the end of a single patch output

When running "format-patch" on a multiple patch series, the output
coming from "--interdiff" and "--range-diff" options is inserted
after the "shortlog" list of commits and the overall diffstat.

The idea is that shortlog/diffstat are shorter and with denser
information content, which gives a better overview before the
readers dive into more details of range/inter diff.

When working on a single patch, however, we stuff the inter/range
diff output before the actual patch, next to the diffstat.  This
pushes down the patch text way down with inter/range diff output,
distracting readers.

Move the inter/range diff output to the very end of the output,
after all the patch text is shown.

As the inter/range diff is no longer part of the commentary block
(i.e., what comes after the log message and "---", but before the
patch text), stop producing "---" in the function that generates
them.  But to separate it out visually (note: this is not needed
to help tools like "git apply" that pay attention to the hunk
headers to figure out the length of the hunks), add an extra blank
line between the end of the patch text and the inter/range diff.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

log-tree.c

@@ -684,8 +684,7 @@ static void show_diff_of_diff(struct rev_info *opt)
 		memcpy(&dq, &diff_queued_diff, sizeof(diff_queued_diff));
 		DIFF_QUEUE_CLEAR(&diff_queued_diff);
 
-		next_commentary_block(opt, NULL);
+		fprintf_ln(opt->diffopt.file, "\n%s", opt->idiff_title);
-		fprintf_ln(opt->diffopt.file, "%s", opt->idiff_title);
 		show_interdiff(opt->idiff_oid1, opt->idiff_oid2, 2,
 			       &opt->diffopt);
 
@@ -704,8 +703,7 @@ static void show_diff_of_diff(struct rev_info *opt)
 		memcpy(&dq, &diff_queued_diff, sizeof(diff_queued_diff));
 		DIFF_QUEUE_CLEAR(&diff_queued_diff);
 
-		next_commentary_block(opt, NULL);
+		fprintf_ln(opt->diffopt.file, "\n%s", opt->rdiff_title);
-		fprintf_ln(opt->diffopt.file, "%s", opt->rdiff_title);
 		/*
 		 * Pass minimum required diff-options to range-diff; others
 		 * can be added later if deemed desirable.
@@ -903,8 +901,6 @@ void show_log(struct rev_info *opt)
 	strbuf_release(&msgbuf);
 	free(ctx.notes_message);
 	free(ctx.after_subject);
-
-	show_diff_of_diff(opt);
 }
 
 int log_tree_diff_flush(struct rev_info *opt)
@@ -1173,9 +1169,12 @@ int log_tree_commit(struct rev_info *opt, struct commit *commit)
 	}
 	if (opt->track_linear && !opt->linear && opt->reverse_output_stage)
 		fprintf(opt->diffopt.file, "\n%s\n", opt->break_bar);
+	if (shown)
+		show_diff_of_diff(opt);
 	opt->loginfo = NULL;
 	maybe_flush_or_die(opt->diffopt.file, "stdout");
 	opt->diffopt.no_free = no_free;
+
 	diff_free(&opt->diffopt);
 	return shown;
 }

t/t4014-format-patch.sh

@@ -2482,13 +2482,37 @@ test_expect_success 'interdiff: reroll-count with a integer' '
 '
 
 test_expect_success 'interdiff: solo-patch' '
-	cat >expect <<-\EOF &&
-	  +fleep
-
-	EOF
 	git format-patch --interdiff=boop~2 -1 boop &&
-	test_grep "^Interdiff:$" 0001-fleep.patch &&
+
-	sed "1,/^  @@ /d; /^$/q" 0001-fleep.patch >actual &&
+	# remove up to the last "patch" output line,
+	# and remove everything below the signature mark.
+	sed -e "1,/^+fleep\$/d" -e "/^-- /,\$d" 0001-fleep.patch >actual &&
+
+	# fabricate Interdiff output.
+	git diff boop~2 boop >inter &&
+	{
+		echo &&
+		echo "Interdiff:" &&
+		sed -e "s/^/  /" inter
+	} >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'range-diff: solo-patch' '
+	git format-patch --creation-factor=999 \
+		--range-diff=boop~2..boop~1 -1 boop &&
+
+	# remove up to the last "patch" output line,
+	# and remove everything below the signature mark.
+	sed -e "1,/^+fleep\$/d" -e "/^-- /,\$d" 0001-fleep.patch >actual &&
+
+	# fabricate range-diff output.
+	{
+		echo &&
+		echo "Range-diff:" &&
+		git range-diff --creation-factor=999 \
+			boop~2..boop~1 boop~1..boop
+	} >expect &&
 	test_cmp expect actual
 '