tustvold opened a new issue, #3265:
URL: https://github.com/apache/arrow-rs/issues/3265
**Describe the bug**
<!--
A clear and concise description of what the bug is.
-->
```
#[test]
fn test_cast_decimal128_to_decimal256_negative() {
let input_type = DataType::Decimal128(10, 3);
let output_type = DataType::Decimal256(10, 5);
assert!(can_cast_types(&input_type, &output_type));
let array = vec![Some(i128::MAX), Some(i128::MIN)];
let input_decimal_array = create_decimal_array(array, 10,
3).unwrap();
let array = Arc::new(input_decimal_array) as ArrayRef;
let hundred = i256::from_i128(100);
generate_cast_test_case!(
&array,
Decimal256Array,
&output_type,
vec![
Some(i256::from_i128(i128::MAX).mul_wrapping(hundred)),
Some(i256::from_i128(i128::MIN).mul_wrapping(hundred))
]
);
}
```
Fails with
```
thread 'cast::tests::test_cast_decimal128_to_decimal256_negative' panicked
at 'assertion failed: `(left == right)`
left: `0`,
right: `17014118346046923173168730371588410572700`',
arrow-cast/src/cast.rs:7251:9
```
The issue is that it is not performing the scaling operation in the
destination type
```
let iter = array.iter().map(|v| {
v.and_then(|v| v.mul_checked(mul).ok().map(i256::from_i128))
});
let casted_array = unsafe {
PrimitiveArray::<Decimal256Type>::from_trusted_len_iter(iter)
};
casted_array
.with_precision_and_scale(*output_precision, *output_scale)
.map(|a| Arc::new(a) as ArrayRef)
```
**To Reproduce**
<!--
Steps to reproduce the behavior:
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**Expected behavior**
<!--
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-->
**Additional context**
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