fix and tests

Author: JeroenSchmidt

pyiceberg/io/pyarrow.py

@@ -1970,13 +1970,14 @@ def _cast_if_needed(self, field: NestedField, values: pa.Array) -> pa.Array:
                             return values.cast(target_type)
                     raise ValueError(f"Unsupported schema projection from {values.type} to {target_type}")
                 elif isinstance(field.field_type, (IntegerType, LongType)):
-                    # Cast smaller integer types to target type for cross-platform compatibility
-                    # Only allow widening conversions (smaller bit width to larger)
-                    # Narrowing conversions fall through to promote() handling below
+                    # Cast integer types for cross-platform compatibility (e.g. Spark reads):
+                    # widening (smaller bit width to larger) and unsigned-to-signed at same width
                     if pa.types.is_integer(values.type):
                         source_width = values.type.bit_width
                         target_width = target_type.bit_width
-                        if source_width < target_width:
+                        if source_width < target_width or (
+                            pa.types.is_unsigned_integer(values.type) and source_width <= target_width
+                        ):
                             return values.cast(target_type)
 
             if field.field_type != file_field.field_type:

tests/io/test_pyarrow.py

@@ -3084,6 +3084,7 @@ def test__to_requested_schema_timestamps_without_downcast_raises_exception(
         (pa.int8(), IntegerType(), pa.int32()),
         (pa.int16(), IntegerType(), pa.int32()),
         (pa.uint16(), IntegerType(), pa.int32()),
+        (pa.uint32(), IntegerType(), pa.int32()),
         (pa.uint32(), LongType(), pa.int64()),
         (pa.int32(), LongType(), pa.int64()),
     ],