Add SEARCH_ALL_VISIBLE_TOOTS env flag

Context: https://docs.joinmastodon.org/user/network/#search

Vanilla Mastodon intentionally refuses to search outside a user's
own toots, favs, bookmarks, and mentions. This flag makes that
restricted search behavior a per-instance choice, defaulting
to the same behavior as vanilla Mastodon if the flag is absent.

.env.production.sample

@@ -283,6 +283,11 @@ MAX_POLL_OPTION_CHARS=100
 # Customize the number of hashtags shown in 'Explore'
 # MAX_TRENDING_TAGS=10
 
+# Search all visible toots
+# (Normally searches only a user's own toots, favs, bookmarks, and mentions)
+# Only relevant when elasticsearch is installed
+# SEARCH_ALL_VISIBLE_TOOTS=true
+
 # Maximum custom emoji file sizes
 # If undefined or smaller than MAX_EMOJI_SIZE, the value
 # of MAX_EMOJI_SIZE will be used for MAX_REMOTE_EMOJI_SIZE

app/chewy/statuses_index.rb

@@ -71,5 +71,6 @@ class StatusesIndex < Chewy::Index
     end
 
     field :searchable_by, type: 'long', value: ->(status, crutches) { status.searchable_by(crutches) }
+    field :searchable_by_anyone, type: 'boolean', value: ->(status) { status.public_visibility? or status.unlisted_visibility? }
   end
 end

app/services/search_service.rb

@@ -1,6 +1,9 @@
 # frozen_string_literal: true
 
 class SearchService < BaseService
+
+  SEARCH_ALL_VISIBLE_TOOTS = ENV['SEARCH_ALL_VISIBLE_TOOTS'] == 'true'
+
   def call(query, account, limit, options = {})
     @query   = query&.strip
     @account = account
@@ -35,7 +38,11 @@ class SearchService < BaseService
   end
 
   def perform_statuses_search!
-    definition = parsed_query.apply(StatusesIndex.filter(term: { searchable_by: @account.id }))
+    statuses_index = StatusesIndex.filter(term: { searchable_by: @account.id })
+    if SEARCH_ALL_VISIBLE_TOOTS
+      statuses_index = statuses_index.or.filter(term: { searchable_by_anyone: true })
+    end
+    definition = parsed_query.apply(statuses_index)
 
     if @options[:account_id].present?
       definition = definition.filter(term: { account_id: @options[:account_id] })