rebar_compiler_dag: store/load dag using internal knowledge

Saves a few seconds when loading DAG with thousands of files.
Unfortunately, uses internal knowledge about digraph implementation.

src/rebar_compiler_dag.erl

@@ -7,17 +7,19 @@
 
 -include("rebar.hrl").
 
--define(DAG_VSN, 3).
+-define(DAG_VSN, 4).
 -define(DAG_ROOT, "source").
 -define(DAG_EXT, ".dag").
 
--type dag_v() :: {digraph:vertex(), term()} | 'false'.
--type dag_e() :: {digraph:vertex(), digraph:vertex()}.
--type critical_meta() :: term(). % if this changes, the DAG is invalid
--type dag_rec() :: {list(dag_v()), list(dag_e()), critical_meta()}.
--type dag() :: digraph:graph().
+-type critical_meta() :: term().
+
 -record(dag, {vsn = ?DAG_VSN :: pos_integer(),
-              info = {[], [], []} :: dag_rec()}).
+    meta :: critical_meta(),
+    vtab :: notable | [tuple()],
+    etab :: notable | [tuple()],
+    ntab :: notable | [tuple()]}).
+
+-type dag() :: digraph:graph().
 
 %% @doc You should initialize one DAG per compiler module.
 %% `CritMeta' is any contextual information that, if it is found to change,
@@ -253,19 +255,23 @@ restore_dag(G, File, CritMeta) ->
         {ok, Data} ->
             %% The CritMeta value is checked and if it doesn't match, we fail
             %% the whole restore operation.
-            #dag{vsn=?DAG_VSN, info={Vs, Es, CritMeta}} = binary_to_term(Data),
-            [digraph:add_vertex(G, V, LastUpdated) || {V, LastUpdated} <- Vs],
-            [digraph:add_edge(G, V1, V2, Label) || {_, V1, V2, Label} <- Es],
+            #dag{vsn=?DAG_VSN, meta = CritMeta, vtab = VTab,
+                etab = ETab, ntab = NTab} = binary_to_term(Data),
+            {digraph, VT, ET, NT, false} = G,
+            true = ets:insert_new(VT, VTab),
+            true = ets:insert_new(ET, ETab),
+            true = ets:delete_all_objects(NT),
+            true = ets:insert(NT, NTab),
             ok;
         {error, _Err} ->
             ok
     end.
 
 store_dag(G, File, CritMeta) ->
     ok = filelib:ensure_dir(File),
-    Vs = lists:map(fun(V) -> digraph:vertex(G, V) end, digraph:vertices(G)),
-    Es = lists:map(fun(E) -> digraph:edge(G, E) end, digraph:edges(G)),
-    Data = term_to_binary(#dag{info={Vs, Es, CritMeta}}, [{compressed, 2}]),
+    {digraph, VT, ET, NT, false} = G,
+    Data = term_to_binary(#dag{meta = CritMeta, vtab = ets:tab2list(VT),
+        etab = ets:tab2list(ET), ntab = ets:select(NT, [{'_',[],['$_']}])}, [{compressed, 2}]),
     file:write_file(File, Data).
 
 %% Drop a file from the digraph if it doesn't exist, and if so,