streams: Show message retention policy details in subscription_type text.

This commit adds message retention policy details in the subscription_type
text below the stream description.

We do not show any text when realm-level settings is set to forever and
stream-level is set to either forever or realm_default.

frontend_tests/node_tests/stream_events.js

@@ -160,7 +160,7 @@ run_test('update_property', () => {
     // Test stream message_retention_days change event
     with_overrides(function (override) {
         global.with_stub(function (stub) {
-            override('stream_data.update_message_retention_setting', stub.f);
+            override('subs.update_message_retention_setting', stub.f);
             stream_events.update_property(1, 'message_retention_days', 20);
             const args = stub.get_args('sub', 'val');
             assert.equal(args.sub.stream_id, 1);

static/js/stream_edit.js

@@ -63,6 +63,30 @@ exports.get_users_from_subscribers = function (subscribers) {
     });
 };
 
+exports.get_retention_policy_text_for_subscription_type = function (sub) {
+    let message_retention_days = sub.message_retention_days;
+    // If both this stream and the organization-level policy are to retain forever,
+    // there's no need to comment on retention policies when describing the stream.
+    if ((page_params.realm_message_retention_days === -1 ||
+         page_params.realm_message_retention_days === null)
+            && (sub.message_retention_days === null || sub.message_retention_days === -1)) {
+        return;
+    }
+
+    // Forever for this stream, overriding the organization default
+    if (sub.message_retention_days === -1) {
+        return i18n.t("Messages in this stream will be retained forever.");
+    }
+
+    // If we are deleting messages, even if it's the organization
+    // default, it's worth commenting on the policy.
+    if (message_retention_days === null)  {
+        message_retention_days = page_params.realm_message_retention_days;
+    }
+
+    return i18n.t("Messages in this stream will be automatically deleted after __retention_days__ days.", {retention_days: message_retention_days});
+};
+
 exports.get_display_text_for_realm_message_retention_setting = function () {
     const realm_message_retention_days = page_params.realm_message_retention_days;
     if (realm_message_retention_days === -1 || realm_message_retention_days === null) {
@@ -315,6 +339,7 @@ exports.show_settings_for = function (node) {
         sub: sub,
         settings: exports.stream_settings(sub),
         stream_post_policy_values: stream_data.stream_post_policy_values,
+        message_retention_text: exports.get_retention_policy_text_for_subscription_type(sub),
     });
     ui.get_content_element($('.subscriptions .right .settings')).html(html);
 

static/js/stream_events.js

@@ -56,7 +56,7 @@ exports.update_property = function (stream_id, property, value, other_values) {
         subs.update_stream_post_policy(sub, value);
         break;
     case 'message_retention_days':
-        stream_data.update_message_retention_setting(sub, value);
+        subs.update_message_retention_setting(sub, value);
         break;
     default:
         blueslip.warn("Unexpected subscription property type", {property: property,

static/js/stream_ui_updates.js

@@ -146,6 +146,7 @@ exports.update_stream_subscription_type_text = function (sub) {
     const template_data = {
         ...sub,
         stream_post_policy_values: stream_data.stream_post_policy_values,
+        message_retention_text: stream_edit.get_retention_policy_text_for_subscription_type(sub),
     };
     const html = render_subscription_type(template_data);
     if (stream_edit.is_sub_settings_active(sub)) {

static/js/subs.js

@@ -192,6 +192,11 @@ exports.update_stream_post_policy = function (sub, new_value) {
     stream_ui_updates.update_stream_subscription_type_text(sub);
 };
 
+exports.update_message_retention_setting = function (sub, new_value) {
+    stream_data.update_message_retention_setting(sub, new_value);
+    stream_ui_updates.update_stream_subscription_type_text(sub);
+};
+
 exports.set_color = function (stream_id, color) {
     const sub = stream_data.get_sub_by_id(stream_id);
     stream_edit.set_stream_property(sub, 'color', color);

static/templates/subscription_settings.hbs

@@ -35,7 +35,8 @@
         <div class="subscription-type">
             <div class="subscription-type-text">
                 {{> subscription_type
-                  stream_post_policy_values=../stream_post_policy_values}}
+                  stream_post_policy_values=../stream_post_policy_values
+                  message_retention_text=../message_retention_text}}
             </div>
             <a class="change-stream-privacy" {{#unless can_change_stream_permissions}}style="display: none;"{{/unless}}>[{{t "Change" }}]</a>
         </div>

static/templates/subscription_type.hbs

@@ -15,3 +15,4 @@
 {{else}}
 {{t 'All stream members can post.'}}
 {{/if}}
+{{message_retention_text}}