refactor: Call compose_fade without triggers.

We are trying to phase out the trigger-event way
of telling modules to do something.

In this case we not only remove the indirection
of the event handler, but we also get to remove
`compose_fade` from the `ui_init` startup sequence.

This also has us update `compose_fade` outside
the loop, although that's only a theoretical
improvement, since I don't think `peer_add` events
every actually include multiple streams.

To make the dispatch tests a little flatter, I
added a one-line change to zjsunit to add
`make_stub` to `global`.

To manually test:
    * have Aaron reply to Denmark (keep compose box open)
    * have Iago add Hamlet to Denmark
    * have Hamlet unsubscribe

frontend_tests/node_tests/dispatch.js

@@ -646,6 +646,9 @@ with_overrides(function (override) {
         });
     });
 
+    const compose_fade_stub = global.make_stub();
+    override('compose_fade.update_faded_users', compose_fade_stub.f);
+
     event = event_fixtures.subscription__peer_add;
     global.with_stub(function (stub) {
         override('stream_data.add_subscriber', stub.f);
@@ -654,6 +657,7 @@ with_overrides(function (override) {
         assert_same(args.sub, event.subscriptions[0]);
         assert_same(args.user_id, 555);
     });
+    assert.equal(compose_fade_stub.num_calls, 1);
 
     event = event_fixtures.subscription__peer_remove;
     global.with_stub(function (stub) {
@@ -663,6 +667,7 @@ with_overrides(function (override) {
         assert_same(args.sub, event.subscriptions[0]);
         assert_same(args.user_id, 555);
     });
+    assert.equal(compose_fade_stub.num_calls, 2);
 
     event = event_fixtures.subscription__remove;
     let stream_id_looked_up;

frontend_tests/node_tests/ui_init.js

@@ -108,7 +108,6 @@ zrequire('tutorial');
 zrequire('notifications');
 zrequire('pointer');
 zrequire('pm_conversations');
-zrequire('compose_fade');
 zrequire('pm_list');
 zrequire('list_cursor');
 zrequire('keydown_util');

frontend_tests/zjsunit/index.js

@@ -44,6 +44,7 @@ global.to_$ = () => window;
 
 // Set up stub helpers.
 const stub = require('./stub.js');
+global.make_stub = stub.make_stub;
 global.with_stub = stub.with_stub;
 
 // Set up fake jQuery

static/js/compose_fade.js

@@ -239,11 +239,4 @@ exports.update_rendered_message_groups = function (message_groups, get_element)
     }
 };
 
-exports.initialize = function () {
-    $(document).on('peer_subscribe.zulip peer_unsubscribe.zulip', function () {
-        exports.update_faded_users();
-    });
-};
-
-
 window.compose_fade = exports;

static/js/server_events_dispatch.js

@@ -335,6 +335,7 @@ exports.dispatch_normal_event = function dispatch_normal_event(event) {
                     blueslip.warn('Cannot process peer_add event');
                 }
             }
+            compose_fade.update_faded_users();
         } else if (event.op === 'peer_remove') {
             for (const sub of event.subscriptions) {
                 if (stream_data.remove_subscriber(sub, event.user_id)) {
@@ -343,6 +344,7 @@ exports.dispatch_normal_event = function dispatch_normal_event(event) {
                     blueslip.warn('Cannot process peer_remove event.');
                 }
             }
+            compose_fade.update_faded_users();
         } else if (event.op === 'remove') {
             for (const rec of event.subscriptions) {
                 const sub = stream_data.get_sub_by_id(rec.stream_id);

static/js/ui_init.js

@@ -475,7 +475,6 @@ exports.initialize_everything = function () {
     presence.initialize(presence_params);
     activity.initialize();
     emoji_picker.initialize();
-    compose_fade.initialize();
     pm_list.initialize();
     topic_list.initialize();
     topic_zoom.initialize();