yongster opened a new pull request, #10707:
URL: https://github.com/apache/arrow-rs/pull/10707
# Which issue does this PR close?
- Closes #10706.
# Rationale for this change
`cast` / `cast_with_options` from an integer array to `Decimal32` or
`Decimal64` can rewrite the value instead of rejecting it.
`cast_integer_to_decimal` first used `AsPrimitive` (`as`), which wraps when
the source integer does not fit the decimal native type. The precision check
then ran on the already-truncated value. If that wrapped value happened to
fit the requested precision, it was stored as if it were the original number.
Examples on current `main`:
- `Int64(5_000_000_000) -> Decimal32(9, 0)` (`safe: true`) becomes
`705032704`
- `UInt32(4_000_000_000) -> Decimal32(9, 0)` (`safe: false`) becomes
`-294967296`
- `UInt64::MAX -> Decimal64(18, 0)` (`safe: false`) becomes `-1`
The same inputs cast to `Decimal128` already return null / `Err`, because
`i64 as i128` is lossless.
# What changes are included in this PR?
- Convert the source integer through a range-checked `i128` path
(`num_cast` + `DecimalCast`) before applying scale and precision.
- `safe: true` writes null when the original value does not fit; `safe:
false`
returns `Err` and reports the original value.
- Add regression tests for `Int64 -> Decimal32`, `UInt32 -> Decimal32`, and
`UInt64::MAX -> Decimal64`.
# Are these changes tested?
Yes. I ran:
```text
cargo test -p arrow-cast --lib -- cast
cargo clippy -p arrow-cast --all-targets --all-features -- -D warnings
cargo +stable fmt --all -- --check
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