Cache vsn info to avoid expensive vcs cmd calls

src/rebar.erl

@@ -96,6 +96,9 @@ run_aux(Commands) ->
     %% Initialize logging system
     rebar_log:init(),
 
+    %% Initialize vsn cache
+    _VsnCacheTab = ets:new(rebar_vsn_cache,[named_table, public]),
+
     %% Convert command strings to atoms
     CommandAtoms = [list_to_atom(C) || C <- Commands],
 

src/rebar_core.erl

@@ -90,6 +90,9 @@ process_commands([Command | Rest], ParentConfig) ->
         _ ->
             ok
     end,
+    %% Wipe out vsn cache to avoid invalid hits when
+    %% dependencies are updated
+    ets:delete_all_objects(rebar_vsn_cache),
     process_commands(Rest, ParentConfig).
 
 

src/rebar_utils.erl

@@ -189,6 +189,17 @@ expand_env_variable(InStr, VarName, RawVarValue) ->
     end.
 
 vcs_vsn(Vcs, Dir) ->
+    Key = {Vcs, Dir},
+    case ets:lookup(rebar_vsn_cache, Key) of
+        [{Key, VsnString}] ->
+            VsnString;
+        [] ->
+            VsnString = vcs_vsn_1(Vcs, Dir),
+            ets:insert(rebar_vsn_cache, {Key, VsnString}),
+            VsnString
+    end.
+
+vcs_vsn_1(Vcs, Dir) ->
     case vcs_vsn_cmd(Vcs) of
         {unknown, VsnString} ->
             ?DEBUG("vcs_vsn: Unknown VCS atom in vsn field: ~p\n", [Vcs]),