feat: enhance exception message on conversion error (#2)

* feat: enhance exception message on conversion error

* chore: bump to 0.2.0

Author: clintval

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "typeline"
-version = "0.1.0"
+version = "0.2.0"
 description = "Write dataclasses to delimited text formats and read them back again."
 authors = ["Clint Valentine <[email protected]>"]
 license = "MIT"

tests/test_reader.py

@@ -4,6 +4,7 @@
 from typing import get_origin
 
 import pytest
+from msgspec import ValidationError
 from typing_extensions import override
 
 from typeline import CsvStructReader
@@ -259,3 +260,26 @@ def _decode(record_type: type[Any] | str | Any, item: Any) -> Any:
 
     with SimpleListReader.from_path(tmp_path / "test.txt", MyMetric) as reader:
         assert list(reader) == [MyMetric(0.1, [1, 2, 3])]
+
+
+def test_reader_msgspec_validation_exception(tmp_path: Path) -> None:
+    """Test that we clarify when msgspec cannot decode a structure of builtins."""
+
+    @dataclass
+    class MyData:
+        field1: str
+        field2: list[int]
+
+    (tmp_path / "test.txt").write_text("field1,field2\nmy-name,null\n")
+
+    with CsvStructReader.from_path(tmp_path / "test.txt", MyData) as reader:
+        with pytest.raises(
+            ValidationError,
+            match=(
+                r"Could not parse JSON-like object into requested structure:"
+                + r" \{'field1'\: 'my-name', 'field2': None\}."
+                + r" Requested structure: MyData. Original exception:"
+                + r" Expected \`array\`, got \`null\` - at \`\$.field2\`"
+            ),
+        ):
+            list(reader)

typeline/_reader.py

@@ -20,6 +20,7 @@
 from typing import get_args
 from typing import get_origin
 
+from msgspec import ValidationError
 from msgspec import convert
 from typing_extensions import Self
 from typing_extensions import override
@@ -164,11 +165,11 @@ def __iter__(self) -> Iterator[RecordType]:
             as_builtins = self._csv_dict_to_json(record)
             try:
                 yield convert(as_builtins, self._record_type, strict=False)
-            except ValueError as exception:
-                raise ValueError(
-                    f"Could not parse {record} as {self._record_type.__name__}!"
-                    + f" Intermediate structure formed is: {as_builtins}."
-                    + f" Original error: {exception}"
+            except ValidationError as exception:
+                raise ValidationError(
+                    f"Could not parse JSON-like object into requested structure: {as_builtins}."
+                    + f" Requested structure: {self._record_type.__name__}."
+                    + f" Original exception: {exception}"
                 ) from exception
 
     @staticmethod