Deduplicate variable names in Template MissingVariables error

llm/templates.py

@@ -76,7 +76,7 @@ def interpolate(cls, text: str | None, params: dict[str, Any]) -> str | None:
         # Confirm all variables in text are provided
         string_template = string.Template(text)
         vars = cls.extract_vars(string_template)
-        missing = [p for p in vars if p not in params]
+        missing = list(dict.fromkeys(p for p in vars if p not in params))
         if missing:
             raise cls.MissingVariables(
                 "Missing variables: {}".format(", ".join(missing))

tests/test_templates.py

@@ -21,6 +21,9 @@
         ("S: $input", "system", None, {}, "S: input", "system", None),
         ("No vars", None, None, {}, "No vars", None, None),
         ("$one and $two", None, None, {}, None, None, "Missing variables: one, two"),
+        # A variable reused in the template is reported once, not once per use.
+        ("$name and $name", None, None, {}, None, None, "Missing variables: name"),
+        ("$a $b $a", None, None, {}, None, None, "Missing variables: a, b"),
         ("$one and $two", None, None, {"one": 1, "two": 2}, "1 and 2", None, None),
         ("$one and $two", None, {"one": 1}, {"two": 2}, "1 and 2", None, None),
         ("$one and $$2", None, None, {"one": 1}, "1 and $2", None, None),