fix(machinery): better handle placeholders in OpenAI

Do not confuse it by talking about placeholders when there are none, it
then tends to hallucinate and add ones.

docs/changes.rst

@@ -12,6 +12,8 @@ Not yet released.
 
 **Bug fixes**
 
+* Improved handling placeables in :ref:`mt-openai`.
+
 **Compatibility**
 
 **Upgrading**

weblate/machinery/base.py

@@ -112,6 +112,8 @@ class BatchMachineTranslation:
     settings_form: None | type[BaseMachineryForm] = None
     request_timeout = 5
     is_available = True
+    replacement_start = "[X"
+    replacement_end = "X]"
 
     @classmethod
     def get_rank(cls):
@@ -317,7 +319,7 @@ def format_replacement(
         self, h_start: int, h_end: int, h_text: str, h_kind: None | Unit
     ) -> str:
         """Generate a single replacement."""
-        return f"[X{h_start}X]"
+        return f"{self.replacement_start}{h_start}{self.replacement_end}"
 
     def get_highlights(
         self, text: str, unit

weblate/machinery/openai.py

@@ -41,7 +41,7 @@
 You always reply with translated string only.
 You do not include transliteration.
 {separator}
-You treat strings like {placeable_1} or {placeable_2} as placeables for user input and keep them intact.
+{placeables}
 {glossary}
 """
 SEPARATOR = "\n==WEBLATE_PART==\n"
@@ -53,6 +53,9 @@
 Use the following glossary during the translation:
 {}
 """
+PLACEABLES_PROMPT = """
+You treat strings like {placeable_1} or {placeable_2} as placeables for user input and keep them intact.
+"""
 
 
 class OpenAITranslation(BatchMachineTranslation):
@@ -97,7 +100,7 @@ def format_prompt_part(self, name: Literal["style", "persona"]):
         return text
 
     def get_prompt(
-        self, source_language: str, target_language: str, units: list
+        self, source_language: str, target_language: str, texts: list[str], units: list
     ) -> str:
         glossary = ""
         if any(units):
@@ -107,15 +110,21 @@ def get_prompt(
             if glossary:
                 glossary = GLOSSARY_PROMPT.format(glossary)
         separator = SEPARATOR_PROMPT if len(units) > 1 else ""
+        placeables = ""
+        if any(self.replacement_start in text for text in texts):
+            placeables = PLACEABLES_PROMPT.format(
+                placeable_1=self.format_replacement(0, -1, "", None),
+                placeable_2=self.format_replacement(123, -1, "", None),
+            )
+
         return PROMPT.format(
             source_language=source_language,
             target_language=target_language,
             persona=self.format_prompt_part("persona"),
             style=self.format_prompt_part("style"),
             glossary=glossary,
             separator=separator,
-            placeable_1=self.format_replacement(0, -1, "", None),
-            placeable_2=self.format_replacement(123, -1, "", None),
+            placeables=placeables,
         )
 
     def download_multiple_translations(
@@ -128,7 +137,7 @@ def download_multiple_translations(
     ) -> DownloadMultipleTranslations:
         texts = [text for text, _unit in sources]
         units = [unit for _text, unit in sources]
-        prompt = self.get_prompt(source, language, units)
+        prompt = self.get_prompt(source, language, texts, units)
         messages = [
             ChatCompletionSystemMessageParam(role="system", content=prompt),
             ChatCompletionUserMessageParam(role="user", content=SEPARATOR.join(texts)),