DEV: Indicate source and target languages in error prompt

app/services/discourse_translator/amazon.rb

@@ -109,42 +109,46 @@ def self.access_token_key
 
     def self.detect(topic_or_post)
       text = truncate text_for_detection(topic_or_post)
-
       return if text.blank?
 
-      begin
-        detected_lang =
+      topic_or_post.custom_fields[DiscourseTranslator::DETECTED_LANG_CUSTOM_FIELD] ||= (
+        begin
           client.translate_text(
             {
               text: text,
               source_language_code: "auto",
               target_language_code: SUPPORTED_LANG_MAPPING[I18n.locale],
             },
           )&.source_language_code
-
-        assign_lang_custom_field(topic_or_post, detected_lang)
-      rescue Aws::Errors::MissingCredentialsError
-        raise I18n.t("translator.amazon.invalid_credentials")
-      end
+        rescue Aws::Errors::MissingCredentialsError
+          raise I18n.t("translator.amazon.invalid_credentials")
+        end
+      )
     end
 
     def self.translate(topic_or_post)
-      from_custom_fields(topic_or_post) do
-        result =
-          client.translate_text(
-            {
-              text: truncate(text_for_translation(topic_or_post)),
-              source_language_code: "auto",
-              target_language_code: SUPPORTED_LANG_MAPPING[I18n.locale],
-            },
-          )
+      detected_lang = detect(topic_or_post)
 
-        detected_lang = assign_lang_custom_field(topic_or_post, result.source_language_code)
+      from_custom_fields(topic_or_post) do
+        begin
+          result =
+            client.translate_text(
+              {
+                text: truncate(text_for_translation(topic_or_post)),
+                source_language_code: "auto",
+                target_language_code: SUPPORTED_LANG_MAPPING[I18n.locale],
+              },
+            )
+        rescue Aws::Translate::Errors::UnsupportedLanguagePairException
+          raise I18n.t(
+                  "translator.failed",
+                  source_locale: detected_lang,
+                  target_locale: I18n.locale,
+                )
+        end
 
         [detected_lang, result.translated_text]
       end
-    rescue Aws::Translate::Errors::UnsupportedLanguagePairException
-      raise I18n.t("translator.failed")
     end
 
     def self.client

app/services/discourse_translator/google.rb

@@ -105,7 +105,9 @@ def self.translate(topic_or_post)
       # here we handle that situation by returning the original string if the source and target lang are the same.
       return detected_lang, get_text(topic_or_post) if (detected_lang&.to_s.eql? I18n.locale.to_s)
 
-      raise I18n.t("translator.failed") unless translate_supported?(detected_lang, I18n.locale)
+      unless translate_supported?(detected_lang, I18n.locale)
+        raise I18n.t("translator.failed", source_locale: detected_lang, target_locale: I18n.locale)
+      end
 
       translated_text =
         from_custom_fields(topic_or_post) do

app/services/discourse_translator/libre_translate.rb

@@ -103,7 +103,9 @@ def self.translate_supported?(source, target)
     def self.translate(topic_or_post)
       detected_lang = detect(topic_or_post)
 
-      raise I18n.t("translator.failed") unless translate_supported?(detected_lang, I18n.locale)
+      unless translate_supported?(detected_lang, I18n.locale)
+        raise I18n.t("translator.failed", source_locale: detected_lang, target_locale: I18n.locale)
+      end
 
       translated_text =
         from_custom_fields(topic_or_post) do

app/services/discourse_translator/microsoft.rb

@@ -112,7 +112,13 @@ def self.translate(topic_or_post)
 
       if !SUPPORTED_LANG_MAPPING.keys.include?(detected_lang.to_sym) &&
            !SUPPORTED_LANG_MAPPING.values.include?(detected_lang.to_s)
-        raise TranslatorError.new(I18n.t("translator.failed"))
+        raise TranslatorError.new(
+                I18n.t(
+                  "translator.failed",
+                  source_locale: detected_lang,
+                  target_locale: I18n.locale,
+                ),
+              )
       end
 
       if get_text(topic_or_post).length > LENGTH_LIMIT

app/services/discourse_translator/yandex.rb

@@ -141,7 +141,13 @@ def self.translate(topic_or_post)
 
       if !SUPPORTED_LANG_MAPPING.keys.include?(detected_lang.to_sym) &&
            !SUPPORTED_LANG_MAPPING.values.include?(detected_lang.to_s)
-        raise TranslatorError.new(I18n.t("translator.failed"))
+        raise TranslatorError.new(
+                I18n.t(
+                  "translator.failed",
+                  source_locale: detected_lang,
+                  target_locale: I18n.locale,
+                ),
+              )
       end
 
       translated_text =

config/locales/server.en.yml

@@ -18,7 +18,7 @@ en:
     restrict_translation_by_group: "Only allowed groups can translate"
     restrict_translation_by_poster_group: "Only allow translation of posts made by users in allowed groups. If empty, allow translations of posts from all users."
   translator:
-    failed: "The translator is unable to translate this language."
+    failed: "The translator is unable to translate this content (%{source_locale}) to the default language of this site (%{target_locale})."
     not_supported: "This language is not supported by the translator."
     too_long: "This post is too long to be translated by the translator."
     not_available: "The translator service is currently not available."

spec/services/amazon_spec.rb

@@ -65,10 +65,15 @@
         },
       )
       described_class.stubs(:client).returns(client)
+      post.custom_fields[::DiscourseTranslator::DETECTED_LANG_CUSTOM_FIELD] = "en"
+      post.save_custom_fields
+      I18n.stubs(:locale).returns(:es)
     end
 
     it "raises an error when trying to translate an unsupported language" do
-      expect { described_class.translate(post) }.to raise_error(I18n.t("translator.failed"))
+      expect { described_class.translate(post) }.to raise_error(
+        I18n.t("translator.failed", source_locale: "en", target_locale: "es"),
+      )
     end
   end
 end

spec/services/google_spec.rb

@@ -167,6 +167,20 @@
       expect { described_class.translate(post) }.to raise_error DiscourseTranslator::TranslatorError
     end
 
+    it "returns error with source and target locale when translation is not supported" do
+      post.custom_fields[DiscourseTranslator::DETECTED_LANG_CUSTOM_FIELD] = "cat"
+      post.save_custom_fields
+      I18n.stubs(:locale).returns(:dog)
+
+      Excon.expects(:post).returns(
+        mock_response.new(200, %{ { "data": { "languages": [ { "language": "kit" }] } } }),
+      )
+
+      expect { described_class.translate(post) }.to raise_error(
+        I18n.t("translator.failed", source_locale: "cat", target_locale: "dog"),
+      )
+    end
+
     it "truncates text for translation to max_characters_per_translation setting" do
       SiteSetting.max_characters_per_translation = 50
       post.cooked = "a" * 100

spec/services/microsoft_spec.rb

@@ -179,7 +179,7 @@ def translate_endpoint
 
         expect { described_class.translate(post) }.to raise_error(
           DiscourseTranslator::TranslatorError,
-          I18n.t("translator.failed"),
+          I18n.t("translator.failed", source_locale: "donkey", target_locale: I18n.locale),
         )
       end