neilconway opened a new issue, #10665:
URL: https://github.com/apache/arrow-rs/issues/10665
### Describe the bug
When casting strings to `Decimal256`, an input whose unscaled value exceeds
the `i256` range is handled incorrectly; it is converted to an incorrect result
value (due to wrapping of the internal i256 representation), rather than being
rejected.
### To Reproduce
```
```rust
use arrow_array::{cast::AsArray, types::Decimal256Type, StringArray};
use arrow_cast::{cast_with_options, CastOptions};
use arrow_schema::DataType;
use std::sync::Arc;
fn main() {
// ~7.2 x 10^64: 65 integer digits and 33 fractional digits
let input =
"72167486952390333280550343777716101824043691957654319462507011489.831702916080743443465428641160496";
let array = Arc::new(StringArray::from(vec![input])) as
arrow_array::ArrayRef;
let options = CastOptions { safe: false, ..Default::default() };
let result = cast_with_options(&array, &DataType::Decimal256(76, 17),
&options).unwrap();
println!("{}",
result.as_primitive::<Decimal256Type>().value_as_string(0));
}
```
Results
```
67335233014482809727371051363254493174014793837924915072256.89984486799063144
```
### Expected behavior
A cast error, because the input is not representable as `Decimal256` (it
requires 82 decimal digits, but `Decimal256` tops out at ~77 decimal digits).
### Additional context
_No response_
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