range_set: fix coalescing bug when range is a subset of another

When coalescing ranges, sort_and_merge_range_set() unconditionally
assumes that the end of a range being folded into a preceding range
should become the end of the coalesced range. This assumption, however,
is invalid when one range is a subset of another.  For example, given
ranges 1-5 and 2-3 added via range_set_append_unsafe(),
sort_and_merge_range_set() incorrectly coalesces them to range 1-3
rather than the correct union range 1-5. Fix this bug.

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

line-log.c

@@ -116,7 +116,8 @@ static void sort_and_merge_range_set(struct range_set *rs)
 
 	for (i = 1; i < rs->nr; i++) {
 		if (rs->ranges[i].start <= rs->ranges[o-1].end) {
-			rs->ranges[o-1].end = rs->ranges[i].end;
+			if (rs->ranges[o-1].end < rs->ranges[i].end)
+				rs->ranges[o-1].end = rs->ranges[i].end;
 		} else {
 			rs->ranges[o].start = rs->ranges[i].start;
 			rs->ranges[o].end = rs->ranges[i].end;

t/t4211-line-log.sh

@@ -50,8 +50,8 @@ canned_test "-M -L ':f:b.c' parallel-change" parallel-change-f-to-main
 canned_test "-L 4,12:a.c -L :main:a.c simple" multiple
 canned_test "-L 4,18:a.c -L :main:a.c simple" multiple-overlapping
 canned_test "-L :main:a.c -L 4,18:a.c simple" multiple-overlapping
-canned_test_failure "-L 4:a.c -L 8,12:a.c simple" multiple-superset
-canned_test_failure "-L 8,12:a.c -L 4:a.c simple" multiple-superset
+canned_test "-L 4:a.c -L 8,12:a.c simple" multiple-superset
+canned_test "-L 8,12:a.c -L 4:a.c simple" multiple-superset
 
 test_bad_opts "-L" "switch.*requires a value"
 test_bad_opts "-L b.c" "argument.*not of the form"