fix(types): validate DecimalType scale, not just precision

DecimalType only bounded precision (1-38) via a model validator; scale
was accepted unbounded, including negative or larger than precision,
and flowed unchecked into downstream type construction and binding.
Add an equivalent check enforcing 0 <= scale <= precision, and fix
pre-existing test fixtures across the suite that relied on scale >
precision or negative scale.

Fixes #3981

Author: ArulJerald

pyiceberg/types.py

@@ -334,6 +334,15 @@ def check_precision(self) -> DecimalType:
             raise ValidationError(f"Decimal precision must be between 1 and 38 (inclusive), got: {precision}")
         return self
 
+    @model_validator(mode="after")
+    def check_scale(self) -> DecimalType:
+        precision = getattr(self, "precision", None) or self.root[0]
+        scale = getattr(self, "scale", None) or self.root[1]
+
+        if not (0 <= scale <= precision):
+            raise ValidationError(f"Decimal scale must be between 0 and the precision {precision} (inclusive), got: {scale}")
+        return self
+
     @model_serializer
     def ser_model(self) -> str:
         """Serialize the model to a string."""

tests/avro/test_reader.py

@@ -282,7 +282,7 @@ def test_fixed_reader() -> None:
 
 
 def test_decimal_reader() -> None:
-    assert construct_reader(DecimalType(19, 25)) == DecimalReader(19, 25)
+    assert construct_reader(DecimalType(25, 19)) == DecimalReader(25, 19)
 
 
 def test_boolean_reader() -> None:

tests/avro/test_resolver.py

@@ -205,7 +205,7 @@ def test_resolve_float_to_double() -> None:
 
 def test_resolve_decimal_to_decimal() -> None:
     # DecimalType(P, S) to DecimalType(P2, S) where P2 > P
-    assert resolve_reader(DecimalType(19, 25), DecimalType(22, 25)) == DecimalReader(19, 25)
+    assert resolve_reader(DecimalType(19, 10), DecimalType(22, 10)) == DecimalReader(19, 10)
 
 
 def test_struct_not_aligned() -> None:
@@ -251,9 +251,9 @@ def test_decimal_not_aligned() -> None:
 def test_resolve_decimal_to_decimal_reduce_precision() -> None:
     # DecimalType(P, S) to DecimalType(P2, S) where P2 > P
     with pytest.raises(ResolveError) as exc_info:
-        _ = resolve_reader(DecimalType(19, 25), DecimalType(10, 25)) == DecimalReader(22, 25)
+        _ = resolve_reader(DecimalType(19, 10), DecimalType(10, 10)) == DecimalReader(22, 10)
 
-    assert "Cannot reduce precision from decimal(19, 25) to decimal(10, 25)" in str(exc_info.value)
+    assert "Cannot reduce precision from decimal(19, 10) to decimal(10, 10)" in str(exc_info.value)
 
 
 def test_resolve_decimal_to_decimal_change_scale() -> None:

tests/avro/test_writer.py

@@ -81,7 +81,7 @@ def test_fixed_writer() -> None:
 
 
 def test_decimal_writer() -> None:
-    assert construct_writer(DecimalType(19, 25)) == DecimalWriter(19, 25)
+    assert construct_writer(DecimalType(25, 19)) == DecimalWriter(25, 19)
 
 
 def test_boolean_writer() -> None:

tests/table/test_partitioning.py

@@ -225,7 +225,7 @@ def test_partition_type_missing_source_field(table_schema_simple: Schema) -> Non
     [
         (IntegerType(), 22),
         (LongType(), 22),
-        (DecimalType(5, 9), Decimal(19.25)),
+        (DecimalType(9, 5), Decimal(19.25)),
         (DateType(), datetime.date(1925, 5, 22)),
         (TimeType(), datetime.time(19, 25, 00)),
         (TimestampType(), datetime.datetime(2022, 5, 1, 22, 1, 1)),

tests/test_conversions.py

@@ -569,7 +569,7 @@ def test_datetime_obj_to_bytes(primitive_type: PrimitiveType, value: datetime |
         (DoubleType(), 1.0, 1.0),
         (DecimalType(9, 4), Decimal("123.4500"), "123.4500"),
         (DecimalType(9, 0), Decimal("2"), "2"),
-        (DecimalType(9, -20), Decimal("2E+20"), "2E+20"),
+        (DecimalType(9, 9), Decimal("0.123456789"), "0.123456789"),
         (DateType(), date(2017, 11, 16), "2017-11-16"),
         (TimeType(), time(22, 31, 8, 123456), "22:31:08.123456"),
         (TimestampType(), datetime(2017, 11, 16, 22, 31, 8, 123456), "2017-11-16T22:31:08.123456"),
@@ -594,7 +594,7 @@ def test_json_single_serialization(primitive_type: PrimitiveType, value: Any, ex
         (DoubleType(), 1.0),
         (DecimalType(9, 4), Decimal("123.4500")),
         (DecimalType(9, 0), Decimal("2")),
-        (DecimalType(9, -20), Decimal("2E+20")),
+        (DecimalType(9, 9), Decimal("0.123456789")),
         (DateType(), date(2017, 11, 16)),
         (TimeType(), time(22, 31, 8, 123456)),
         (TimestampType(), datetime(2017, 11, 16, 22, 31, 8, 123456)),

tests/test_schema.py

@@ -1105,7 +1105,7 @@ def test_add_nested_lists(primitive_fields: NestedField, table_v2: Table) -> Non
                                     element_id=7,
                                     element_type=ListType(
                                         element_id=8,
-                                        element_type=ListType(element_id=9, element_type=DecimalType(precision=11, scale=20)),
+                                        element_type=ListType(element_id=9, element_type=DecimalType(precision=20, scale=11)),
                                         element_required=False,
                                     ),
                                     element_required=False,

tests/test_types.py

@@ -504,14 +504,14 @@ def test_repr_binary() -> None:
 
 
 def test_serialization_decimal() -> None:
-    assert DecimalType(19, 25).model_dump_json() == '"decimal(19, 25)"'
+    assert DecimalType(25, 19).model_dump_json() == '"decimal(25, 19)"'
 
 
 def test_deserialization_decimal() -> None:
-    decimal = DecimalType.model_validate_json('"decimal(19, 25)"')
-    assert decimal == DecimalType(19, 25)
-    assert decimal.precision == 19
-    assert decimal.scale == 25
+    decimal = DecimalType.model_validate_json('"decimal(25, 19)"')
+    assert decimal == DecimalType(25, 19)
+    assert decimal.precision == 25
+    assert decimal.scale == 19
 
 
 def test_deserialization_decimal_failure() -> None:
@@ -522,11 +522,11 @@ def test_deserialization_decimal_failure() -> None:
 
 
 def test_str_decimal() -> None:
-    assert str(DecimalType(19, 25)) == "decimal(19, 25)"
+    assert str(DecimalType(25, 19)) == "decimal(25, 19)"
 
 
 def test_repr_decimal() -> None:
-    assert repr(DecimalType(19, 25)) == "DecimalType(precision=19, scale=25)"
+    assert repr(DecimalType(25, 19)) == "DecimalType(precision=25, scale=19)"
 
 
 def test_repr_nested_field_default_nones_should_not_appear() -> None:
@@ -935,3 +935,15 @@ def test_decimal_precision_validation() -> None:
 
     with pytest.raises(ValidationError, match="Decimal precision must be between 1 and 38"):
         DecimalType(-5, 2)
+
+
+def test_decimal_scale_validation() -> None:
+    """Test that DecimalType rejects a scale that is negative or exceeds the precision."""
+    assert DecimalType(9, 9).scale == 9
+    assert DecimalType(9, 0).scale == 0
+
+    with pytest.raises(ValidationError, match="Decimal scale must be between 0 and the precision"):
+        DecimalType(10, -1)
+
+    with pytest.raises(ValidationError, match="Decimal scale must be between 0 and the precision"):
+        DecimalType(5, 10)

tests/utils/test_schema_conversion.py

@@ -317,9 +317,9 @@ def test_avro_list_missing_element_id() -> None:
 
 
 def test_convert_decimal_type() -> None:
-    avro_decimal_type = {"type": "bytes", "logicalType": "decimal", "precision": 19, "scale": 25}
+    avro_decimal_type = {"type": "bytes", "logicalType": "decimal", "precision": 25, "scale": 19}
     actual = AvroSchemaConversion()._convert_logical_type(avro_decimal_type)
-    expected = DecimalType(precision=19, scale=25)
+    expected = DecimalType(precision=25, scale=19)
     assert actual == expected