neilconway opened a new issue, #10664:
URL: https://github.com/apache/arrow-rs/issues/10664
### Describe the bug
Casting a string to a decimal type fails if the input has more than ~76
fractional digits. This is suboptimal, because digits beyond the target scale
only matter for rounding, and the correct result is easily representable in the
target type.
### To Reproduce
```rust
use arrow_array::{cast::AsArray, types::Decimal128Type, StringArray};
use arrow_cast::{cast_with_options, CastOptions};
use arrow_schema::DataType;
use std::sync::Arc;
fn main() {
// 0.111... with 80 fractional digits; at scale 4 this is exactly 0.1111
let input = format!("0.{}", "1".repeat(80));
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::Decimal128(38, 4),
&options);
println!("{result:?}");
}
```
Result
```
Err(CastError("Cannot cast string '0.11111...11111' to value of
Decimal128(38, 10) type"))
```
### Expected behavior
This should succeed and print `0.1111`, following the rounding behavior we
use for shorter inputs.
### Additional context
_No response_
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