chore(appup): make update_appup.escript output only differences for

external dependencies

Currently, the update_appup.escript outputs as an error the full appup
file for external dependencies, even if all the changes are already
contained in the depency.  Here, we make it only output the missing
actions to be inserted, to aid in seeing what are the differences.

scripts/update_appup.escript

@@ -99,8 +99,31 @@ main(Options, Baseline) ->
                 [] ->
                     ok;
                 _ ->
-                    set_invalid(),
-                    log("ERROR: The appup files are incomplete. Missing changes:~n   ~p", [AppupChanges])
+                    Diffs =
+                        lists:filtermap(
+                          fun({App, {Upgrade, Downgrade, OldUpgrade, OldDowngrade}}) ->
+                                  DiffUp = diff_appup_instructions(Upgrade, OldUpgrade),
+                                  DiffDown = diff_appup_instructions(Downgrade, OldDowngrade),
+                                  case {DiffUp, DiffDown} of
+                                      {[], []} ->
+                                          %% no diff for external dependency
+                                          false;
+                                      _ ->
+                                          Diffs = #{ up => DiffUp
+                                                   , down => DiffDown
+                                                   },
+                                          {true, {App, Diffs}}
+                                  end
+                          end,
+                          AppupChanges),
+                    case Diffs =:= [] of
+                        true ->
+                            ok;
+                        false ->
+                            set_invalid(),
+                            log("ERROR: The appup files are incomplete. Missing changes:~n   ~p",
+                                [Diffs])
+                    end
             end;
         false ->
             update_appups(AppupChanges)
@@ -189,9 +212,35 @@ find_appup_actions(App, CurrAppIdx, PrevAppIdx = #app{version = PrevVersion}) ->
             %% The appup file has been already updated:
             [];
        true ->
-            [{App, {Upgrade, Downgrade}}]
+            [{App, {Upgrade, Downgrade, OldUpgrade, OldDowngrade}}]
     end.
 
+%% For external dependencies, show only the changes that are missing
+%% in their current appup.
+diff_appup_instructions(ComputedChanges, PresentChanges) ->
+    lists:foldr(
+      fun({Vsn, ComputedActions}, Acc) ->
+              case find_matching_version(Vsn, PresentChanges) of
+                  undefined ->
+                      [{Vsn, ComputedActions} | Acc];
+                  PresentActions ->
+                      DiffActions = ComputedActions -- PresentActions,
+                      case DiffActions of
+                          [] ->
+                              %% no diff
+                              Acc;
+                          _ ->
+                              [{Vsn, DiffActions} | Acc]
+                      end
+              end
+      end,
+      [],
+      ComputedChanges).
+
+%% TODO: handle regexes
+find_matching_version(Vsn, PresentChanges) ->
+    proplists:get_value(Vsn, PresentChanges).
+
 find_old_appup_actions(App, PrevVersion) ->
     {Upgrade0, Downgrade0} =
         case locate(ebin_current, App, ".appup") of
@@ -270,12 +319,12 @@ check_appup_files() ->
 
 update_appups(Changes) ->
     lists:foreach(
-      fun({App, {Upgrade, Downgrade}}) ->
-              do_update_appup(App, Upgrade, Downgrade)
+      fun({App, {Upgrade, Downgrade, OldUpgrade, OldDowngrade}}) ->
+              do_update_appup(App, Upgrade, Downgrade, OldUpgrade, OldDowngrade)
       end,
       Changes).
 
-do_update_appup(App, Upgrade, Downgrade) ->
+do_update_appup(App, Upgrade, Downgrade, OldUpgrade, OldDowngrade) ->
     case locate(src, App, ".appup.src") of
         {ok, AppupFile} ->
             render_appfile(AppupFile, Upgrade, Downgrade);
@@ -284,8 +333,20 @@ do_update_appup(App, Upgrade, Downgrade) ->
                 {ok, AppupFile} ->
                     render_appfile(AppupFile, Upgrade, Downgrade);
                 false ->
-                    set_invalid(),
-                    log("ERROR: Appup file for the external dependency '~p' is not complete.~n       Missing changes: ~p~n", [App, Upgrade])
+                    DiffUp = diff_appup_instructions(Upgrade, OldUpgrade),
+                    DiffDown = diff_appup_instructions(Downgrade, OldDowngrade),
+                    case {DiffUp, DiffDown} of
+                        {[], []} ->
+                            %% no diff for external dependency; ignore
+                            ok;
+                        _ ->
+                            set_invalid(),
+                            Diffs = #{ up => DiffUp
+                                     , down => DiffDown
+                                     },
+                            log("ERROR: Appup file for the external dependency '~p' is not complete.~n       Missing changes: ~100p~n", [App, Diffs]),
+                            log("NOTE: Some changes above might be already covered by regexes.~n")
+                    end
             end
     end.