Fix all clippy lints in parquet crate

[alamb]

Describe the bug
Due to "historical reasons" there are several clippy lints that are disabled in the parquet crate
https://github.com/apache/arrow-rs/blob/master/parquet/src/lib.rs#L18-L36

#![allow(incomplete_features)]
#![allow(dead_code)]
#![allow(non_camel_case_types)]
#![allow(
    clippy::approx_constant,
    clippy::cast_ptr_alignment,
    clippy::float_cmp,
    clippy::float_equality_without_abs,
    clippy::from_over_into,
    clippy::many_single_char_names,
    clippy::needless_range_loop,
    clippy::new_without_default,
    clippy::or_fun_call,
    clippy::same_item_push,
    clippy::too_many_arguments,
    clippy::transmute_ptr_to_ptr,
    clippy::upper_case_acronyms,
    clippy::vec_init_then_push
)]

It would be great to clean up the code to pass these lints for tidiness

To Reproduce
Remove one of the #[allow] lines above, run clippy

Expected behavior
Clippy runs cleanly without blank #allow across the whole crate

Additional context
Add any other context about the problem here.

[HaoYang670]

I'd like to have a try if no one else has been doing it!
Rust Clippy is really interesting!

[HaoYang670]

There are many dead code and unused public functions. I am not sure whether to clean them up.

[alamb]

There are many dead code and unused public functions. I am not sure whether to clean them up.

I recommend doing this issue in a few PRs -- in the first take care of the easier lints, and then in follow ons we can sort out dead code / public function nonsense together

[HaoYang670]

Lots of pub members are detected as dead code. I am not sure whether to clean them up. For example:

warning: enum is never used: `LevelDecoder`
   --> parquet/src/encodings/levels.rs:151:10
    |
151 | pub enum LevelDecoder {
    |          ^^^^^^^^^^^^

warning: associated function is never used: `v1`
   --> parquet/src/encodings/levels.rs:165:12
    |
165 |     pub fn v1(encoding: Encoding, max_level: i16) -> Self {
    |            ^^

warning: associated function is never used: `v2`
   --> parquet/src/encodings/levels.rs:180:12
    |
180 |     pub fn v2(max_level: i16) -> Self {
    |            ^^

warning: associated function is never used: `set_data`
   --> parquet/src/encodings/levels.rs:194:12
    |
194 |     pub fn set_data(&mut self, num_buffered_values: usize, data: ByteBufferPtr) -> usize {
    |            ^^^^^^^^

warning: associated function is never used: `set_data_range`
   --> parquet/src/encodings/levels.rs:221:12
    |
221 |     pub fn set_data_range(
    |            ^^^^^^^^^^^^^^

warning: associated function is never used: `is_data_set`
   --> parquet/src/encodings/levels.rs:242:12
    |
242 |     pub fn is_data_set(&self) -> bool {
    |            ^^^^^^^^^^^

warning: associated function is never used: `get`
   --> parquet/src/encodings/levels.rs:254:12
    |
254 |     pub fn get(&mut self, buffer: &mut [i16]) -> Result<usize> {
    |            ^^^

warning: associated function is never used: `buffer`
   --> parquet/src/encodings/rle.rs:171:12
    |
171 |     pub fn buffer(&self) -> &[u8] {
    |            ^^^^^^

warning: associated function is never used: `get`
   --> parquet/src/encodings/rle.rs:358:12
    |
358 |     pub fn get<T: FromBytes>(&mut self) -> Result<Option<T>> {

[alamb]

Sorry for the late reply @HaoYang670

Lots of pub members are detected as dead code. I am not sure whether to clean them up. For example:

If the code is dead I think we should remove it. One way for pub functions to be dead is if the module they are defined in is not pub.

I am not sure how you are running clippy, but it may also be that some of these structs are only used when certain features of the parquet crate are enabled.

I believe our CI system has good coverage so feel free to try removing them and if the CI passes I think it is a good change

[HaoYang670]

but it may also be that some of these structs are only used when certain features of the parquet crate are enabled.

Thank you @alamb. There are some experimental mods under parquet. And I have to run cargo clippy --features experimental to make them public. But I am not sure whether our CI adds this flag.

[alamb]

Clippy is run like this:

https://github.com/apache/arrow-rs/blob/master/.github/workflows/rust.yml#L211-L250

          cargo clippy --features test_common --features prettyprint  --features=async --all-targets --workspace -- -D warnings

Perhaps we can also add the experimental features to this list?

[alamb]

After #2190 clippy is run just for the parquet crate (which now includes the --experimental flag)

So once that is merged, the first order of business will be to make this command run cleanly:

cargo clippy -p parquet --all-targets --all-features -- -D warnings

And then we can move on to removing the additional lints