add runtime validation of syntax

this makes coverage drop dramatically

Author: matthewfranglen

pydantic_ai_slim/pydantic_ai/tools.py

@@ -179,6 +179,8 @@ def __post_init__(self) -> None:
                 re.compile(self.grammar)
             except re.error as e:
                 raise ValueError('Regex is invalid') from e
+        else:
+            raise ValueError(f'Unsupported syntax {self.syntax}')
 
 
 class GenerateToolJsonSchema(GenerateJsonSchema):

tests/test_tools.py

@@ -1496,6 +1496,11 @@ def test_function_text_format_lark_invalid():
         FunctionTextFormat(syntax='lark', grammar='invalid grammar [')
 
 
+def test_function_text_format_syntax_invalid():
+    with pytest.raises(ValueError, match='Unsupported syntax antlr'):
+        FunctionTextFormat(syntax='antlr', grammar="grammar T; a: 'a';")
+
+
 def test_tool_definition_single_string_argument():
     schema = {
         'type': 'object',