bookend: Simplify can_toggle_subscription variable flow.

frontend_tests/node_tests/message_list.js

@@ -312,6 +312,7 @@ run_test("bookend", ({override}) => {
 
     override(stream_data, "is_subscribed_by_name", () => is_subscribed);
     override(stream_data, "get_sub", () => ({invite_only}));
+    override(stream_data, "can_toggle_subscription", () => true);
 
     {
         const stub = make_stub();
@@ -323,13 +324,11 @@ run_test("bookend", ({override}) => {
             "subscribed",
             "deactivated",
             "just_unsubscribed",
-            "show_button",
         );
         assert.equal(bookend.stream_name, "IceCream");
         assert.equal(bookend.subscribed, true);
         assert.equal(bookend.deactivated, false);
         assert.equal(bookend.just_unsubscribed, false);
-        assert.equal(bookend.show_button, true);
     }
 
     list.last_message_historical = false;
@@ -345,13 +344,11 @@ run_test("bookend", ({override}) => {
             "subscribed",
             "deactivated",
             "just_unsubscribed",
-            "show_button",
         );
         assert.equal(bookend.stream_name, "IceCream");
         assert.equal(bookend.subscribed, false);
         assert.equal(bookend.deactivated, false);
         assert.equal(bookend.just_unsubscribed, true);
-        assert.equal(bookend.show_button, true);
     }
 
     // Test when the stream is privates (invite only)
@@ -367,13 +364,11 @@ run_test("bookend", ({override}) => {
             "subscribed",
             "deactivated",
             "just_unsubscribed",
-            "show_button",
         );
         assert.equal(bookend.stream_name, "IceCream");
         assert.equal(bookend.subscribed, false);
         assert.equal(bookend.deactivated, false);
         assert.equal(bookend.just_unsubscribed, true);
-        assert.equal(bookend.show_button, false);
     }
 
     list.last_message_historical = true;
@@ -388,13 +383,11 @@ run_test("bookend", ({override}) => {
             "subscribed",
             "deactivated",
             "just_unsubscribed",
-            "show_button",
         );
         assert.equal(bookend.stream_name, "IceCream");
         assert.equal(bookend.subscribed, false);
         assert.equal(bookend.deactivated, false);
         assert.equal(bookend.just_unsubscribed, false);
-        assert.equal(bookend.show_button, true);
     }
 });
 

static/js/message_list.js

@@ -244,23 +244,21 @@ export class MessageList {
 
         let deactivated = false;
         let just_unsubscribed = false;
-        let show_button = true;
         const subscribed = stream_data.is_subscribed_by_name(stream_name);
         const sub = stream_data.get_sub(stream_name);
+        const can_toggle_subscription =
+            sub !== undefined && stream_data.can_toggle_subscription(sub);
         if (sub === undefined) {
             deactivated = true;
-            // Hide the resubscribe button for streams that no longer exist.
-            show_button = false;
         } else if (!subscribed && !this.last_message_historical) {
             just_unsubscribed = true;
-            show_button = stream_data.can_toggle_subscription(sub);
         }
         this.view.render_trailing_bookend(
             stream_name,
             subscribed,
             deactivated,
             just_unsubscribed,
-            show_button,
+            can_toggle_subscription,
             page_params.is_spectator,
         );
     }

static/js/message_list_view.js

@@ -1300,13 +1300,13 @@ export class MessageListView {
         subscribed,
         deactivated,
         just_unsubscribed,
-        show_button,
+        can_toggle_subscription,
         is_spectator,
     ) {
         const rendered_trailing_bookend = $(
             render_bookend({
                 stream_name,
-                trailing: show_button,
+                can_toggle_subscription,
                 subscribed,
                 deactivated,
                 just_unsubscribed,

static/templates/bookend.hbs

@@ -1,5 +1,5 @@
 {{! Client-side Mustache template for rendering the trailing bookend.}}
-<div class="{{#if trailing}}trailing_bookend{{/if}} bookend sub-unsub-message">
+<div class="{{#if can_toggle_subscription}}trailing_bookend{{/if}} bookend sub-unsub-message">
     {{#if is_spectator}}
         <span class="recent-topics-link">
             <a href="#recent_topics">{{t "Browse recent topics" }}</a>
@@ -17,7 +17,7 @@
             {{/if}}
         </span>
     {{/if}}
-    {{#if trailing}}
+    {{#if can_toggle_subscription}}
     <div class="sub_button_row new-style">
         <button class="button white rounded stream_sub_unsub_button {{#unless subscribed}}sea-green{{/unless}}" type="button" name="subscription">
             {{#if subscribed}}