typeddicts: raise proper error on invalid input

Author: Tinche

HISTORY.md

@@ -29,6 +29,8 @@ Our backwards-compatibility policy can be found [here](https://github.com/python
   ([#598](https://github.com/python-attrs/cattrs/pull/598))
 - Preconf converters now handle dictionaries with literal keys properly.
   ([#599](https://github.com/python-attrs/cattrs/pull/599))
+- Structuring TypedDicts from invalid inputs now properly raises a {class}`ClassValidationError`.
+  ([#615](https://github.com/python-attrs/cattrs/issues/615) [#616](https://github.com/python-attrs/cattrs/pull/616))
 - Replace `cattrs.gen.MappingStructureFn` with `cattrs.SimpleStructureHook[In, T]`.
 - Python 3.13 is now supported.
   ([#543](https://github.com/python-attrs/cattrs/pull/543) [#547](https://github.com/python-attrs/cattrs/issues/547))

src/cattrs/gen/typeddicts.py

@@ -307,9 +307,16 @@ def make_dict_structure_fn(
         globs["__c_a"] = allowed_fields
         globs["__c_feke"] = ForbiddenExtraKeysError
 
-    lines.append("  res = o.copy()")
-
     if _cattrs_detailed_validation:
+        # When running under detailed validation, be extra careful about copying
+        # so that the correct error is raised if the input isn't a dict.
+        lines.append("  try:")
+        lines.append("    res = o.copy()")
+        lines.append("  except Exception as exc:")
+        lines.append(
+            f"    raise __c_cve('While structuring ' + {cl.__name__!r}, [exc], __cl)"
+        )
+
         lines.append("  errors = []")
         internal_arg_parts["__c_cve"] = ClassValidationError
         internal_arg_parts["__c_avn"] = AttributeValidationNote
@@ -383,6 +390,7 @@ def make_dict_structure_fn(
             f"  if errors: raise __c_cve('While structuring ' + {cl.__name__!r}, errors, __cl)"
         )
     else:
+        lines.append("  res = o.copy()")
         non_required = []
 
         # The first loop deals with required args.

tests/test_typeddicts.py

@@ -10,7 +10,7 @@
 from pytest import raises
 from typing_extensions import NotRequired, Required
 
-from cattrs import BaseConverter, Converter
+from cattrs import BaseConverter, Converter, transform_error
 from cattrs._compat import ExtensionsTypedDict, get_notrequired_base, is_generic
 from cattrs.errors import (
     ClassValidationError,
@@ -509,3 +509,12 @@ class A(ExtensionsTypedDict):
 
     assert converter.unstructure({"a": 10, "b": 10}, A) == {"a": 1, "b": 2}
     assert converter.structure({"a": 10, "b": 10}, A) == {"a": 1, "b": 2}
+
+
+def test_nondict_input():
+    """Trying to structure typeddict from a non-dict raises the proper exception."""
+    converter = Converter(detailed_validation=True)
+    with raises(ClassValidationError) as exc:
+        converter.structure(1, TypedDictA)
+
+    assert transform_error(exc.value) == ["expected a mapping @ $"]