Jefffrey opened a new issue, #6480:
URL: https://github.com/apache/arrow-rs/issues/6480
**Describe the bug**
<!--
A clear and concise description of what the bug is.
-->
BitIterator panics when retrieving its length via ExactSizeIterator
**To Reproduce**
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Steps to reproduce the behavior:
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```rust
#[test]
fn test123() {
let b = BitIterator::new(&[0b00000010], 0, 2);
dbg!(b.len());
}
```
Output:
```
arrow-rs$ cargo test -p arrow-buffer --lib
util::bit_iterator::tests::test123 -- --nocapture
Blocking waiting for file lock on build directory
Compiling arrow-buffer v53.0.0 (/home/jeffrey/Code/arrow-rs/arrow-buffer)
Finished `test` profile [unoptimized + debuginfo] target(s) in 9.48s
Running unittests src/lib.rs
(/media/jeffrey/1tb_860evo_ssd/.cargo_target_cache/debug/deps/arrow_buffer-9f4040912c29ccf9)
running 1 test
thread 'util::bit_iterator::tests::test123' panicked at
/rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/core/src/iter/traits/exact_size.rs:122:9:
assertion `left == right` failed
left: None
right: Some(0)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
test util::bit_iterator::tests::test123 ... FAILED
failures:
failures:
util::bit_iterator::tests::test123
test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 128 filtered
out; finished in 0.00s
error: test failed, to rerun pass `-p arrow-buffer --lib`
```
**Expected behavior**
<!--
A clear and concise description of what you expected to happen.
-->
Doesn't panic
**Additional context**
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Add any other context about the problem here.
-->
Panic is here:
https://github.com/rust-lang/rust/blob/eeb90cda1969383f56a2637cbd3037bdf598841c/library/core/src/iter/traits/exact_size.rs#L122
Looks like BitIterator implements ExactSizeIterator:
https://github.com/apache/arrow-rs/blob/f41c258246cd4bd9d89228cded9ed54dbd00faff/arrow-buffer/src/util/bit_iterator.rs#L71
But it does not override the default size_hint from Iterator:
https://github.com/apache/arrow-rs/blob/f41c258246cd4bd9d89228cded9ed54dbd00faff/arrow-buffer/src/util/bit_iterator.rs#L56-L69
According to docs:
https://doc.rust-lang.org/std/iter/trait.ExactSizeIterator.html
> When doing so, the implementation of [`Iterator::size_hint`] *must* return
the exact size of the iterator.
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