FIX: 'Show original' button only shows in topics where there are translated content

app/models/concerns/discourse_translator/translatable.rb

@@ -30,7 +30,10 @@ def set_translation(locale, text)
 
     def translation_for(locale)
       locale = locale.to_s.gsub("_", "-")
-      translations.find_by(locale: locale)&.translation
+      # this is a tricky perf balancing act when loading translations for a topic with many posts.
+      # the topic_view_serializer includes(:translations) for posts in the topic,
+      # the alternative is to do a find_by(locale: locale) which would result in a query per post.
+      translations.to_a.find { |t| t.locale == locale }&.translation
     end
 
     def detected_locale

app/models/discourse_translator/post_translation.rb

@@ -10,10 +10,6 @@ class PostTranslation < ActiveRecord::Base
     validates :locale, presence: true
     validates :translation, presence: true
     validates :locale, uniqueness: { scope: :post_id }
-
-    def self.translation_for(post_id, locale)
-      find_by(post_id: post_id, locale: locale)&.translation
-    end
   end
 end
 

app/models/discourse_translator/topic_translation.rb

@@ -10,10 +10,6 @@ class TopicTranslation < ActiveRecord::Base
     validates :locale, presence: true
     validates :translation, presence: true
     validates :locale, uniqueness: { scope: :topic_id }
-
-    def self.translation_for(topic_id, locale)
-      find_by(topic_id: topic_id, locale: locale)&.translation
-    end
   end
 end
 

assets/javascripts/discourse/components/show-original-content.gjs

@@ -6,6 +6,13 @@ import DButton from "discourse/components/d-button";
 import concatClass from "discourse/helpers/concat-class";
 
 export default class ShowOriginalContent extends Component {
+  static shouldRender(args) {
+    return (
+      args.topic.is_translated ||
+      args.topic.postStream.posts.some(({ is_translated }) => is_translated)
+    );
+  }
+
   @service router;
   @tracked isTranslated = true;
 

lib/discourse_translator/guardian_extension.rb

@@ -24,15 +24,17 @@ def can_detect_language?(post)
   def can_translate?(post)
     return false if post.user&.bot?
     return false if !user_group_allow_translate?
-    return false if post.locale_matches?(I18n.locale)
 
     # we want to return false if the post is created within a short buffer ago,
     # this prevents the 🌐from appearing and then disappearing if the lang is same as user's lang
     return false if post.created_at > POST_DETECTION_BUFFER.ago && post.detected_locale.blank?
 
     if SiteSetting.experimental_inline_translation
-      post.translation_for(I18n.locale).nil?
+      locale = DiscourseTranslator::InlineTranslation.effective_locale
+      return false if post.locale_matches?(locale)
+      post.translation_for(locale).nil?
     else
+      return false if post.locale_matches?(I18n.locale)
       poster_group_allow_translate?(post)
     end
   end

lib/discourse_translator/inline_translation.rb

@@ -2,41 +2,69 @@
 
 module DiscourseTranslator
   class InlineTranslation
+    def self.effective_locale
+      if LocaleMatcher.user_locale_is_default? || LocaleMatcher.user_locale_in_target_languages?
+        I18n.locale
+      else
+        SiteSetting.default_locale
+      end
+    end
+
     def inject(plugin)
+      # since locales are eager loaded but translations may not,
+      # always return early if topic and posts are in the user's effective_locale.
+      # this prevents the need to load translations.
+
       plugin.register_modifier(:basic_post_serializer_cooked) do |cooked, serializer|
         if !SiteSetting.experimental_inline_translation ||
-             serializer.scope&.request&.params&.[]("show") == "original" ||
-             serializer.object.detected_locale == I18n.locale.to_s.gsub("_", "-")
+             serializer.object.locale_matches?(InlineTranslation.effective_locale) ||
+             serializer.scope&.request&.params&.[]("show") == "original"
           cooked
         else
-          serializer.object.translation_for(I18n.locale).presence
+          serializer.object.translation_for(InlineTranslation.effective_locale).presence
         end
       end
 
       plugin.register_modifier(:topic_serializer_fancy_title) do |fancy_title, serializer|
         if !SiteSetting.experimental_inline_translation ||
-             serializer.scope&.request&.params&.[]("show") == "original" ||
-             serializer.object.locale_matches?(I18n.locale)
+             serializer.object.locale_matches?(InlineTranslation.effective_locale) ||
+             serializer.scope&.request&.params&.[]("show") == "original"
           fancy_title
         else
-          serializer.object.translation_for(I18n.locale).presence&.then { |t| Topic.fancy_title(t) }
+          serializer
+            .object
+            .translation_for(InlineTranslation.effective_locale)
+            .presence
+            &.then { |t| Topic.fancy_title(t) }
         end
       end
 
       plugin.register_modifier(:topic_view_serializer_fancy_title) do |fancy_title, serializer|
         if !SiteSetting.experimental_inline_translation ||
-             serializer.scope&.request&.params&.[]("show") == "original" ||
-             serializer.object.topic.locale_matches?(I18n.locale)
+             serializer.object.topic.locale_matches?(InlineTranslation.effective_locale) ||
+             serializer.scope&.request&.params&.[]("show") == "original"
           fancy_title
         else
           serializer
             .object
             .topic
-            .translation_for(I18n.locale)
+            .translation_for(InlineTranslation.effective_locale)
             .presence
             &.then { |t| Topic.fancy_title(t) }
         end
       end
+
+      plugin.add_to_serializer(:basic_post, :is_translated) do
+        SiteSetting.experimental_inline_translation &&
+          !object.locale_matches?(InlineTranslation.effective_locale) &&
+          object.translation_for(InlineTranslation.effective_locale).present?
+      end
+
+      plugin.add_to_serializer(:topic_view, :is_translated) do
+        SiteSetting.experimental_inline_translation &&
+          !object.topic.locale_matches?(InlineTranslation.effective_locale) &&
+          object.topic.translation_for(InlineTranslation.effective_locale).present?
+      end
     end
   end
 end

lib/discourse_translator/locale_matcher.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module DiscourseTranslator
+  class LocaleMatcher
+    def self.user_locale_in_target_languages?
+      # e.g. "en|es|pt_BR" vs :en_UK
+      SiteSetting.automatic_translation_target_languages.split("|").include?(I18n.locale.to_s)
+    end
+
+    def self.user_locale_is_default?
+      # e.g. :en_UK vs "en_UK"
+      I18n.locale.to_s == SiteSetting.default_locale
+    end
+  end
+end

lib/discourse_translator/topic_view_serializer_extension.rb

@@ -4,7 +4,20 @@ module DiscourseTranslator
   module TopicViewSerializerExtension
     def posts
       if SiteSetting.translator_enabled?
-        object.instance_variable_set(:@posts, object.posts.includes(:content_locale))
+        posts_query = object.posts.includes(:content_locale)
+        # this is kind of a micro-optimization.
+        # we do not want to eager load translations if the user is using the site's language.
+        # we will only load them if the user is using a different language that is supported by the site.
+        if SiteSetting.experimental_inline_translation && !LocaleMatcher.user_locale_is_default? &&
+             LocaleMatcher.user_locale_in_target_languages?
+          posts_query =
+            posts_query.includes(:translations).where(
+              translations: {
+                locale: InlineTranslation.effective_locale.to_s.gsub("_", "-"),
+              },
+            )
+        end
+        object.instance_variable_set(:@posts, posts_query)
       end
       super
     end

spec/lib/guardian_extension_spec.rb

@@ -177,7 +177,12 @@
       end
 
       describe "when experimental_inline_translation enabled" do
-        before { SiteSetting.experimental_inline_translation = true }
+        before do
+          SiteSetting.experimental_inline_translation = true
+
+          SiteSetting.automatic_translation_backfill_maximum_translations_per_hour = 1
+          SiteSetting.automatic_translation_target_languages = "pt"
+        end
 
         describe "logged in user" do
           it "cannot translate when user is not in restrict_translation_by_group" do
@@ -190,7 +195,7 @@
             before { SiteSetting.restrict_translation_by_group = "#{group.id}" }
 
             it "cannot translate when post has translation for user locale" do
-              post.set_detected_locale("jp")
+              post.set_detected_locale("ja")
               post.set_translation("pt", "Olá, mundo!")
 
               expect(guardian.can_translate?(post)).to eq(false)

spec/serializers/basic_topic_serializer_spec.rb

@@ -20,6 +20,9 @@
       topic.title = original_title
       SiteSetting.experimental_inline_translation = true
       I18n.locale = "ja"
+
+      SiteSetting.automatic_translation_backfill_maximum_translations_per_hour = 1
+      SiteSetting.automatic_translation_target_languages = "ja"
     end
 
     def serialize_topic(guardian_user: user, params: {})
@@ -53,6 +56,14 @@ def serialize_topic(guardian_user: user, params: {})
       expect(serialize_topic.fancy_title).to eq(topic.fancy_title)
     end
 
+    it "does not replace fancy_title when user's locale is not in target languages" do
+      I18n.locale = "es"
+      topic.set_detected_locale("en")
+      topic.set_translation("es", jap_title)
+
+      expect(serialize_topic.fancy_title).to eq(topic.fancy_title)
+    end
+
     it "returns translated title in fancy_title when translation exists for current locale" do
       topic.set_translation("ja", jap_title)
       expect(serialize_topic.fancy_title).to eq("<h1>フス・ロ・ダ・ア</h1>")

spec/serializers/post_serializer_spec.rb

@@ -56,6 +56,63 @@
     end
   end
 
+  describe "#is_translated" do
+    fab!(:post)
+
+    it "returns false when translator disabled" do
+      SiteSetting.translator_enabled = false
+      serializer = PostSerializer.new(post, scope: Guardian.new)
+
+      expect(serializer.is_translated).to eq(false)
+    end
+
+    it "returns false when experimental inline translation disabled" do
+      SiteSetting.translator_enabled = true
+      SiteSetting.experimental_inline_translation = false
+      serializer = PostSerializer.new(post, scope: Guardian.new)
+
+      expect(serializer.is_translated).to eq(false)
+    end
+
+    it "returns true when there is a translation for the user's locale in target languages" do
+      SiteSetting.translator_enabled = true
+      SiteSetting.experimental_inline_translation = true
+      SiteSetting.automatic_translation_backfill_maximum_translations_per_hour = 1
+      SiteSetting.automatic_translation_target_languages = "ja"
+      I18n.locale = "ja"
+      post.set_detected_locale("en")
+      post.set_translation("ja", "こんにちは")
+      serializer = PostSerializer.new(post, scope: Guardian.new)
+
+      expect(serializer.is_translated).to eq(true)
+    end
+
+    it "returns false when there is a translation for the user's locale not in target languages" do
+      SiteSetting.translator_enabled = true
+      SiteSetting.experimental_inline_translation = true
+      SiteSetting.automatic_translation_backfill_maximum_translations_per_hour = 1
+      SiteSetting.automatic_translation_target_languages = "es"
+      I18n.locale = "ja"
+      post.set_detected_locale("en")
+      post.set_translation("ja", "こんにちは")
+      serializer = PostSerializer.new(post, scope: Guardian.new)
+
+      expect(serializer.is_translated).to eq(false)
+    end
+
+    it "returns false when there is no translation for the current locale in target languages" do
+      SiteSetting.translator_enabled = true
+      SiteSetting.experimental_inline_translation = true
+      SiteSetting.automatic_translation_backfill_maximum_translations_per_hour = 1
+      SiteSetting.automatic_translation_target_languages = "ja"
+      I18n.locale = "ja"
+      post.set_translation("es", "Hola")
+      serializer = PostSerializer.new(post, scope: Guardian.new)
+
+      expect(serializer.is_translated).to eq(false)
+    end
+  end
+
   describe "#cooked" do
     def serialize_post(guardian_user: user, params: {})
       env = { "action_dispatch.request.parameters" => params, "REQUEST_METHOD" => "GET" }
@@ -76,6 +133,8 @@ def serialize_post(guardian_user: user, params: {})
 
     it "does not return translated_cooked when show=original param is present" do
       I18n.locale = "ja"
+      SiteSetting.automatic_translation_backfill_maximum_translations_per_hour = 1
+      SiteSetting.automatic_translation_target_languages = "ja"
       post.set_translation("ja", "こんにちは")
 
       expect(serialize_post(params: { "show" => "original" }).cooked).to eq(post.cooked)
@@ -90,11 +149,17 @@ def serialize_post(guardian_user: user, params: {})
       expect(serialize_post.cooked).to eq(post.cooked)
     end
 
-    it "returns translated content based on locale" do
-      I18n.locale = "ja"
+    it "returns translated content based on locale presence in target languages" do
+      SiteSetting.automatic_translation_backfill_maximum_translations_per_hour = 1
       post.set_translation("ja", "こんにちは")
       post.set_translation("es", "Hola")
+      I18n.locale = "ja"
+
+      SiteSetting.automatic_translation_target_languages = "ja"
       expect(serialize_post.cooked).to eq("こんにちは")
+
+      SiteSetting.automatic_translation_target_languages = "es"
+      expect(serialize_post.cooked).to eq(post.cooked)
     end
 
     it "does not return translated_cooked when plugin is disabled" do