[Go] Fix (*BitSet).equals (#3455)

runtime/Go/antlr/utils.go

@@ -169,12 +169,18 @@ func (b *BitSet) equals(other interface{}) bool {
 		return true
 	}
 
-	if len(b.data) != len(otherBitSet.data) {
+	// We only compare set bits, so we cannot rely on the two slices having the same size. Its
+	// possible for two BitSets to have different slice lengths but the same set bits. So we only
+	// compare the relavent words and ignore the trailing zeros.
+	bLen := b.minLen()
+	otherLen := otherBitSet.minLen()
+
+	if bLen != otherLen {
 		return false
 	}
 
-	for k := range b.data {
-		if b.data[k] != otherBitSet.data[k] {
+	for i := 0; i < bLen; i++ {
+		if b.data[i] != otherBitSet.data[i] {
 			return false
 		}
 	}

runtime/Go/antlr/utils_test.go

@@ -53,4 +53,10 @@ func TestBitSet(t *testing.T) {
 	bs3.add(63)
 	bs1.or(bs3)
 	testBitSet(t, bs1, "{63, 64}", 2, []int{63, 64}, 63, 2)
+	bs1.clear(64)
+	bs4 := NewBitSet()
+	bs4.or(bs1)
+	if got, want := bs4.equals(bs1), true; got != want {
+		t.Errorf("%+v.equals(%+v) = %v, want %v", bs4, bs1, got, want)
+	}
 }