Fix mix xref order across OTP versions (OTP 27) (#13430)

Author: sabiwara

lib/mix/lib/mix/tasks/xref.ex

@@ -1003,10 +1003,12 @@ defmodule Mix.Tasks.Xref do
   end
 
   defp cycles(graph, opts) do
+    # Vertices order in cyclic_strong_components/1 return is arbitrary and changes between
+    # OTP versions, sorting is necessary to make the output stable across versions.
     cycles =
       graph
       |> :digraph_utils.cyclic_strong_components()
-      |> Enum.reduce([], &inner_cycles(graph, &1, &2))
+      |> Enum.reduce([], &inner_cycles(graph, Enum.sort(&1), &2))
       |> Enum.map(&{length(&1), &1})
 
     if min = opts[:min_cycle_size], do: Enum.filter(cycles, &(elem(&1, 0) > min)), else: cycles

lib/mix/test/mix/tasks/xref_test.exs

@@ -445,9 +445,9 @@ defmodule Mix.Tasks.XrefTest do
 
       Cycle of length 3:
 
-          lib/b.ex
           lib/a.ex
           lib/b.ex
+          lib/a.ex
 
       """)
     end
@@ -1085,7 +1085,7 @@ defmodule Mix.Tasks.XrefTest do
                  ^first_line | ["Generated sample app" | result]
                ] = receive_until_no_messages([]) |> String.split("\n")
 
-        assert normalize_graph_output(result |> Enum.join("\n")) == expected
+        assert result |> Enum.join("\n") |> normalize_graph_output() == expected
       end)
     end