notifications: Warn if all PM notifications will be disabled.

This PR adds a modal to warn when user unchecks a box on the "PMs,
mentions, and alerts" line of notifications panel that will result in
all notifications for private messages and mentions being disabled.

Fixes #24151.

web/src/settings_notifications.js

@@ -1,9 +1,11 @@
 import $ from "jquery";
 
+import render_confirm_disable_all_notifications from "../templates/confirm_dialog/confirm_disable_all_notifications.hbs";
 import render_stream_specific_notification_row from "../templates/settings/stream_specific_notification_row.hbs";
 
 import * as channel from "./channel";
-import {$t} from "./i18n";
+import * as confirm_dialog from "./confirm_dialog";
+import {$t, $t_html} from "./i18n";
 import * as notifications from "./notifications";
 import {page_params} from "./page_params";
 import * as settings_config from "./settings_config";
@@ -196,6 +198,40 @@ export function set_up(settings_panel) {
             setting_name = "email_notifications_batching_period_seconds";
         }
 
+        if (
+            settings_config.pm_mention_notification_settings.includes(setting_name) &&
+            !setting_value
+        ) {
+            let enabled_pm_mention_notifications_count = 0;
+            const pm_mention_notification_settings =
+                settings_config.get_notifications_table_row_data(
+                    settings_config.pm_mention_notification_settings,
+                    user_settings,
+                );
+
+            for (const setting of pm_mention_notification_settings) {
+                if (setting.is_checked && !setting.is_disabled) {
+                    enabled_pm_mention_notifications_count += 1;
+                }
+            }
+            if (enabled_pm_mention_notifications_count === 1) {
+                const html_body = render_confirm_disable_all_notifications();
+                $input_elem.prop("checked", user_settings[setting_name]);
+
+                confirm_dialog.launch({
+                    html_heading: $t_html({defaultMessage: "Disable notifications?"}),
+                    html_body,
+                    on_click: () =>
+                        change_notification_setting(
+                            setting_name,
+                            setting_value,
+                            $input_elem.closest(".subsection-parent").find(".alert-notification"),
+                        ),
+                });
+                return;
+            }
+        }
+
         change_notification_setting(
             setting_name,
             setting_value,

web/templates/confirm_dialog/confirm_disable_all_notifications.hbs

@@ -0,0 +1,12 @@
+<p>
+    {{#tr}}
+    You are about to disable all notifications for private messages,
+    @&#8209;mentions and alerts, which may cause you to miss messages
+    that require your timely attention.
+    If you would like to temporarily disable all desktop notifications,
+    consider <z-link>turning on "Do not disturb"</z-link> instead.
+    {{#*inline "z-link"}}<a href="/help/do-not-disturb">{{> @partial-block}}</a>{{/inline}}
+    {{/tr}}
+</p>
+
+<p>{{t "Are you sure you want to continue?"}}</p>