Fix scan empty array into multi-dimension slice

pgtype/array_codec_test.go

@@ -126,6 +126,23 @@ func TestArrayCodecScanMultipleDimensions(t *testing.T) {
 	require.NoError(t, rows.Err())
 }
 
+func TestArrayCodecScanMultipleDimensionsEmpty(t *testing.T) {
+	conn := testutil.MustConnectPgx(t)
+	defer testutil.MustCloseContext(t, conn)
+
+	rows, err := conn.Query(context.Background(), `select '{}'::int4[]`)
+	require.NoError(t, err)
+
+	for rows.Next() {
+		var ss [][]int32
+		err := rows.Scan(&ss)
+		require.NoError(t, err)
+		require.Equal(t, [][]int32{}, ss)
+	}
+
+	require.NoError(t, rows.Err())
+}
+
 func TestArrayCodecScanWrongMultipleDimensions(t *testing.T) {
 	conn := testutil.MustConnectPgx(t)
 	defer testutil.MustCloseContext(t, conn)

pgtype/builtin_wrappers.go

@@ -763,7 +763,10 @@ func (a *anyMultiDimSliceArray) SetDimensions(dimensions []ArrayDimension) error
 
 	switch len(dimensions) {
 	case 0:
-		return fmt.Errorf("impossible: non-nil dimensions but zero elements")
+		// Empty, but non-nil array
+		slice := reflect.MakeSlice(sliceType, 0, 0)
+		a.slice.Set(slice)
+		return nil
 	case 1:
 		elementCount := cardinality(dimensions)
 		slice := reflect.MakeSlice(sliceType, elementCount, elementCount)