message view: Refactor top loading indicators.

This commit makes the `loading_older_messages_indicator` similar
to the `loading_newer_messages_indicator`.
Now all the decisions about whether to show a loading indicator
will be made from the `fetch_status` API. We still hide the
indicators everytime the view is changed, as explained in the
previous commit.

frontend_tests/node_tests/fetch_status.js

@@ -1,5 +1,7 @@
 const FetchStatus = zrequire('fetch_status');
 set_global('message_scroll', {
+    hide_loading_older: () => {},
+    show_loading_older: () => {},
     hide_loading_newer: () => {},
     show_loading_newer: () => {},
 });
@@ -54,7 +56,7 @@ run_test('basics', () => {
     reset();
 
     fetch_status.start_newer_batch({ update_loading_indicator: false });
-    fetch_status.start_older_batch();
+    fetch_status.start_older_batch({ update_loading_indicator: false });
 
     blocked_newer();
     blocked_older();
@@ -80,7 +82,7 @@ run_test('basics', () => {
     reset();
 
     fetch_status.start_newer_batch({ update_loading_indicator: true });
-    fetch_status.start_older_batch();
+    fetch_status.start_older_batch({ update_loading_indicator: true });
 
     blocked_newer();
     blocked_older();
@@ -103,13 +105,14 @@ run_test('basics', () => {
 
     can_load_older();
 
-    fetch_status.start_older_batch();
+    fetch_status.start_older_batch({ update_loading_indicator: false });
 
     blocked_older();
     can_load_newer();
     can_load_history();
 
     fetch_status.finish_older_batch({
+        update_loading_indicator: true,
         found_oldest: false,
         history_limited: false,
     });
@@ -118,13 +121,14 @@ run_test('basics', () => {
     can_load_newer();
     can_load_history();
 
-    fetch_status.start_older_batch();
+    fetch_status.start_older_batch({ update_loading_indicator: true });
 
     blocked_older();
     can_load_newer();
     can_load_history();
 
     fetch_status.finish_older_batch({
+        update_loading_indicator: true,
         found_oldest: true,
         history_limited: true,
     });

frontend_tests/node_tests/message_fetch.js

@@ -26,6 +26,8 @@ set_global('ui_report', {
 set_global('channel', {});
 set_global('document', 'document-stub');
 set_global('message_scroll', {
+    show_loading_older: noop,
+    hide_loading_older: noop,
     show_loading_newer: noop,
     hide_loading_newer: noop,
 });

static/js/fetch_status.js

@@ -8,14 +8,20 @@ const FetchStatus = function () {
     let found_newest = false;
     let history_limited = false;
 
-    self.start_older_batch = function () {
+    self.start_older_batch = function (opts) {
         loading_older = true;
+        if (opts.update_loading_indicator) {
+            message_scroll.show_loading_older();
+        }
     };
 
     self.finish_older_batch = function (opts) {
         loading_older = false;
         found_oldest = opts.found_oldest;
         history_limited = opts.history_limited;
+        if (opts.update_loading_indicator) {
+            message_scroll.hide_loading_older();
+        }
     };
 
     self.can_load_older_messages = function () {

static/js/message_fetch.js

@@ -64,6 +64,7 @@ function get_messages_success(data, opts) {
     const update_loading_indicator = opts.msg_list === current_msg_list;
     if (opts.num_before > 0) {
         opts.msg_list.data.fetch_status.finish_older_batch({
+            update_loading_indicator: update_loading_indicator,
             found_oldest: data.found_oldest,
             history_limited: data.history_limited,
         });
@@ -73,6 +74,7 @@ function get_messages_success(data, opts) {
             // which is never rendered (and just used for
             // prepopulating narrowed views).
             message_list.all.data.fetch_status.finish_older_batch({
+                update_loading_indicator: false,
                 found_oldest: data.found_oldest,
                 history_limited: data.history_limited,
             });
@@ -174,9 +176,13 @@ exports.load_messages = function (opts) {
 
     const update_loading_indicator = opts.msg_list === current_msg_list;
     if (opts.num_before > 0) {
-        opts.msg_list.data.fetch_status.start_older_batch();
+        opts.msg_list.data.fetch_status.start_older_batch({
+            update_loading_indicator: update_loading_indicator,
+        });
         if (opts.msg_list === home_msg_list) {
-            message_list.all.data.fetch_status.start_older_batch();
+            message_list.all.data.fetch_status.start_older_batch({
+                update_loading_indicator: update_loading_indicator,
+            });
         }
     }
 
@@ -284,13 +290,9 @@ exports.maybe_load_older_messages = function (opts) {
         return;
     }
 
-    opts.show_loading();
     exports.do_backfill({
         msg_list: msg_list,
         num_before: consts.backward_batch_size,
-        cont: function () {
-            opts.hide_loading();
-        },
     });
 };
 

static/js/message_scroll.js

@@ -63,8 +63,6 @@ exports.scroll_finished = function () {
     if (message_viewport.at_top()) {
         message_fetch.maybe_load_older_messages({
             msg_list: current_msg_list,
-            show_loading: exports.show_loading_older,
-            hide_loading: exports.hide_loading_older,
         });
     }
 

static/js/narrow.js

@@ -299,8 +299,6 @@ exports.activate = function (raw_operators, opts) {
             id_info: id_info,
             select_offset: then_select_offset,
         });
-    } else {
-        message_scroll.show_loading_older();
     }
 
     // Put the narrow operators in the URL fragment.