Paginate ancestor statuses in public page (#7102)

This also limits the statuses returned by API, but pagination is not
implemented in Web API yet. I still expect it brings user experience
better than making a user wait to fetch all ancestor statuses and flooding
the column with them.

app/controllers/api/v1/statuses_controller.rb

@@ -17,7 +17,7 @@ class Api::V1::StatusesController < Api::BaseController
   end
 
   def context
-    ancestors_results   = @status.in_reply_to_id.nil? ? [] : @status.ancestors(current_account)
+    ancestors_results   = @status.in_reply_to_id.nil? ? [] : @status.ancestors(DEFAULT_STATUSES_LIMIT, current_account)
     descendants_results = @status.descendants(current_account)
     loaded_ancestors    = cache_collection(ancestors_results, Status)
     loaded_descendants  = cache_collection(descendants_results, Status)

app/controllers/statuses_controller.rb

@@ -4,6 +4,8 @@ class StatusesController < ApplicationController
   include SignatureAuthentication
   include Authorization
 
+  ANCESTORS_LIMIT = 20
+
   layout 'public'
 
   before_action :set_account
@@ -16,8 +18,9 @@ class StatusesController < ApplicationController
   def show
     respond_to do |format|
       format.html do
-        @ancestors   = @status.reply? ? cache_collection(@status.ancestors(current_account), Status) : []
-        @descendants = cache_collection(@status.descendants(current_account), Status)
+        @ancestors     = @status.reply? ? cache_collection(@status.ancestors(ANCESTORS_LIMIT, current_account), Status) : []
+        @next_ancestor = @ancestors.size < ANCESTORS_LIMIT ? nil : @ancestors.shift
+        @descendants   = cache_collection(@status.descendants(current_account), Status)
 
         render 'stream_entries/show'
       end

app/javascript/styles/mastodon/stream_entries.scss

@@ -6,7 +6,8 @@
     background: $simple-background-color;
 
     .detailed-status.light,
-    .status.light {
+    .status.light,
+    .more.light {
       border-bottom: 1px solid $ui-secondary-color;
       animation: none;
     }
@@ -290,6 +291,17 @@
       text-decoration: underline;
     }
   }
+
+  .more {
+    color: $classic-primary-color;
+    display: block;
+    padding: 14px;
+    text-align: center;
+
+    &:not(:hover) {
+      text-decoration: none;
+    }
+  }
 }
 
 .embed {

app/models/concerns/status_threading_concern.rb

@@ -3,8 +3,8 @@
 module StatusThreadingConcern
   extend ActiveSupport::Concern
 
-  def ancestors(account = nil)
-    find_statuses_from_tree_path(ancestor_ids, account)
+  def ancestors(limit, account = nil)
+    find_statuses_from_tree_path(ancestor_ids(limit), account)
   end
 
   def descendants(account = nil)
@@ -13,14 +13,21 @@ module StatusThreadingConcern
 
   private
 
-  def ancestor_ids
-    Rails.cache.fetch("ancestors:#{id}") do
-      ancestor_statuses.pluck(:id)
+  def ancestor_ids(limit)
+    key = "ancestors:#{id}"
+    ancestors = Rails.cache.fetch(key)
+
+    if ancestors.nil? || ancestors[:limit] < limit
+      ids = ancestor_statuses(limit).pluck(:id).reverse!
+      Rails.cache.write key, limit: limit, ids: ids
+      ids
+    else
+      ancestors[:ids].last(limit)
     end
   end
 
-  def ancestor_statuses
-    Status.find_by_sql([<<-SQL.squish, id: in_reply_to_id])
+  def ancestor_statuses(limit)
+    Status.find_by_sql([<<-SQL.squish, id: in_reply_to_id, limit: limit])
       WITH RECURSIVE search_tree(id, in_reply_to_id, path)
       AS (
         SELECT id, in_reply_to_id, ARRAY[id]
@@ -34,7 +41,8 @@ module StatusThreadingConcern
       )
       SELECT id
       FROM search_tree
-      ORDER BY path DESC
+      ORDER BY path
+      LIMIT :limit
     SQL
   end
 

app/views/stream_entries/_status.html.haml

@@ -14,6 +14,10 @@
   entry_classes = h_class + ' ' + mf_classes + ' ' + style_classes
 
 - if status.reply? && include_threads
+  - if @next_ancestor
+    .entry{ class: entry_classes }
+      = link_to short_account_status_url(@next_ancestor.account.username, @next_ancestor), class: 'more light'  do
+        = t('statuses.show_more')
   = render partial: 'stream_entries/status', collection: @ancestors, as: :status, locals: { is_predecessor: true, direct_reply_id: status.in_reply_to_id }
 
 .entry{ class: entry_classes }