neilconway opened a new issue, #10866:
URL: https://github.com/apache/arrow-rs/issues/10866
### Describe the bug
As discussed in #2387, validating that a decimal value fits within the
declared precision is opt-in; i.e., decimal values that exceed their type's
declared precision is allowed. When such values are displayed/formatted (e.g.,
via `value_as_string`), there is incorrect behavior: either an incorrect value
is produced or a panic occurs.
### To Reproduce
```rust
use arrow_array::Decimal128Array;
use arrow_schema::DataType;
// 1234.5 declared as Decimal128(3, 1)
let a = Decimal128Array::from(vec![12345])
.with_precision_and_scale(3, 1)
.unwrap();
a.value_as_string(0); // "12.3" — expected "1234.5"
// 12.345 declared as Decimal128(3, 3)
let a = Decimal128Array::from(vec![12345])
.with_precision_and_scale(3, 3)
.unwrap();
a.value_as_string(0); // ".123" — expected "12.345"
// 1.2345 declared as Decimal128(2, 4)
let a =
Decimal128Array::from(vec![12345]).with_data_type(DataType::Decimal128(2, 4));
a.value_as_string(0);
```
### Expected behavior
The decimal value should be displayed correctly (i.e., the declared
precision should effectively be ignored for display purposes).
We could in principle produce an error instead of displaying such values,
but this is difficult for practical purposes (e.g., related APIs don't return
`Result` or a similar channel for surfacing errors), and would be inconsistent
with Arrow behavior elsewhere.
### Additional context
_No response_
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