log: teach -L/RE/ to search from end of previous -L range

This is complicated slightly by having to remember the previous -L range
for each file specified via -L<range>:file.

The existing implementation coalesces ranges for each file as each -L is
parsed which makes it impossible to refer back to the previous -L range
for any particular file. Re-implement to instead store each file's set
of -L ranges verbatim, and then coalesce the ranges in a post-processing
step.

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

line-log.c

@@ -291,15 +291,13 @@ static void line_log_data_insert(struct line_log_data **list,
 
 	if (p) {
 		range_set_append_unsafe(&p->ranges, begin, end);
-		sort_and_merge_range_set(&p->ranges);
 		free(path);
 		return;
 	}
 
 	p = xcalloc(1, sizeof(struct line_log_data));
 	p->path = path;
 	range_set_append(&p->ranges, begin, end);
-	sort_and_merge_range_set(&p->ranges);
 	if (ip) {
 		p->next = ip->next;
 		ip->next = p;
@@ -566,12 +564,14 @@ parse_lines(struct commit *commit, const char *prefix, struct string_list *args)
 	struct nth_line_cb cb_data;
 	struct string_list_item *item;
 	struct line_log_data *ranges = NULL;
+	struct line_log_data *p;
 
 	for_each_string_list_item(item, args) {
 		const char *name_part, *range_part;
 		char *full_name;
 		struct diff_filespec *spec;
 		long begin = 0, end = 0;
+		long anchor;
 
 		name_part = skip_range_arg(item->string);
 		if (!name_part || *name_part != ':' || !name_part[1])
@@ -590,8 +590,14 @@ parse_lines(struct commit *commit, const char *prefix, struct string_list *args)
 		cb_data.lines = lines;
 		cb_data.line_ends = ends;
 
+		p = search_line_log_data(ranges, full_name, NULL);
+		if (p && p->ranges.nr)
+			anchor = p->ranges.ranges[p->ranges.nr - 1].end + 1;
+		else
+			anchor = 1;
+
 		if (parse_range_arg(range_part, nth_line, &cb_data,
-				    lines, 1, &begin, &end,
+				    lines, anchor, &begin, &end,
 				    full_name))
 			die("malformed -L argument '%s'", range_part);
 		if (lines < end || ((lines || begin) && lines < begin))
@@ -608,6 +614,9 @@ parse_lines(struct commit *commit, const char *prefix, struct string_list *args)
 		ends = NULL;
 	}
 
+	for (p = ranges; p; p = p->next)
+		sort_and_merge_range_set(&p->ranges);
+
 	return ranges;
 }