treeset: fix a bug in Subset where some non-subsets could trigger panic

shoenig · shoenig · commit c2ca09880588 · 2023-05-06T08:01:16.000-05:00
diff --git a/treeset.go b/treeset.go
@@ -383,7 +383,8 @@ func (s *TreeSet[T, C]) Subset(o *TreeSet[T, C]) bool {
 next:
 	for ; idxO < o.Size(); idxO++ {
 		nextO := <-iterO
-		for ; idxS < s.Size(); idxS++ {
+		for idxS < s.Size() {
+			idxS++
 			nextS := <-iterS
 			cmp := s.compare(nextS, nextO)
 			switch {
diff --git a/treeset_test.go b/treeset_test.go
@@ -321,6 +321,12 @@ func TestTreeSet_Subset(t *testing.T) {
 		t2 := TreeSetFrom[int, Compare[int]]([]int{6, 7, 8, 9, 10}, Cmp[int])
 		must.False(t, t1.Subset(t2))
 	})
+
+	t.Run("exhaust s1", func(t *testing.T) {
+		s1 := TreeSetFrom[string, Compare[string]]([]string{"a", "b", "c", "d", "e"}, Cmp[string])
+		s2 := TreeSetFrom[string, Compare[string]]([]string{"a", "z"}, Cmp[string])
+		must.False(t, s1.Subset(s2))
+	})
 }
 
 func TestTreeSet_Union(t *testing.T) {
