Return cycles in deps solver

src/rebar_digraph.erl

@@ -18,7 +18,15 @@ compile_order(Apps) ->
                   end, Apps),
     case digraph_utils:topsort(Graph) of
         false ->
-            {error, no_sort};
+            case digraph_utils:is_acyclic(Graph) of
+                true ->
+                    {error, no_sort};
+                false ->
+                    Cycles = lists:sort(
+                        [lists:sort(Comp) || Comp <- digraph_utils:strong_components(Graph),
+                                             length(Comp)>1]),
+                    {error, {cycles, Cycles}}
+            end;
         V ->
             {ok, names_to_apps(lists:reverse(V), Apps)}
     end.

test/rebar_deps_SUITE.erl

@@ -47,11 +47,11 @@ deps(pick_earliest) ->
 deps(circular1) ->
     {[{"B", [{"A", []}]}, % A is the top-level app
       {"C", []}],
-     {error, no_sort}}; % circular dep
+     {error, {cycles, [[<<"A">>,<<"B">>]]}}}; % circular dep
 deps(circular2) ->
     {[{"B", [{"C", [{"B", []}]}]},
       {"C", []}],
-     {error, no_sort}}. % circular dep
+     {error, {cycles, [[<<"B">>,<<"C">>]]}}}. % circular dep
 
 end_per_testcase(_, Config) ->
     mock_git_resource:unmock(),