fix(config): stringify pydantic error loc before join (#5884)

Signed-off-by: Anas Khan <83116240+anxkhn@users.noreply.github.com>

Author: anxkhn

sqlmesh/utils/pydantic.py

@@ -242,7 +242,7 @@ def _formatted_validation_errors(error: pydantic.ValidationError) -> t.List[str]
     for e in error.errors():
         msg = e["msg"]
         loc: t.Optional[t.Tuple] = e.get("loc")
-        loc_str = ".".join(loc) if loc else None
+        loc_str = ".".join(str(p) for p in loc) if loc else None
         result.append(f"Invalid field '{loc_str}':\n    {msg}" if loc_str else msg)
     return result
 

tests/core/test_config.py

@@ -702,7 +702,7 @@ def test_load_model_defaults_validation_statements(tmp_path):
         """
         )
 
-    with pytest.raises(TypeError, match=r"expected str instance, int found"):
+    with pytest.raises(ConfigError, match=r"Invalid field 'model_defaults\.pre_statements\.0"):
         config = load_config_from_paths(
             Config,
             project_paths=[config_path],

tests/utils/test_pydantic.py

@@ -2,8 +2,14 @@
 import pytest
 from functools import cached_property
 
+import pydantic
+
 from sqlmesh.utils.date import TimeLike, to_date, to_datetime
-from sqlmesh.utils.pydantic import PydanticModel, get_concrete_types_from_typehint
+from sqlmesh.utils.pydantic import (
+    PydanticModel,
+    get_concrete_types_from_typehint,
+    validation_error_message,
+)
 
 
 def test_datetime_date_serialization() -> None:
@@ -87,3 +93,19 @@ class TestModel(PydanticModel):
 )
 def test_get_concrete_types_from_typehint(input: t.Any, output: set[type]) -> None:
     assert get_concrete_types_from_typehint(input) == output
+
+
+def test_validation_error_message_with_list_index_location() -> None:
+    class Inner(PydanticModel):
+        x: int
+
+    class Outer(PydanticModel):
+        items: t.List[Inner]
+
+    with pytest.raises(pydantic.ValidationError) as ex:
+        Outer(items=[{"x": "not_an_int"}])
+
+    # The error is located at a list index, so pydantic's loc mixes str field
+    # names with an int sequence index (e.g. ("items", 0, "x")).
+    message = validation_error_message(ex.value, "Invalid config:")
+    assert "Invalid field 'items.0.x'" in message