Proc-macros: useless conversion Clippy lint

[ivmarkov]

Consider:

/// Matter service
#[gatt_service(uuid = MATTER_BLE_SERVICE_UUID16)]
struct MatterService {
    #[characteristic(uuid = Uuid::Uuid128(C1_CHARACTERISTIC_UUID.to_be_bytes()), write)]
    c1: External,
    #[characteristic(uuid = Uuid::Uuid128(C2_CHARACTERISTIC_UUID.to_be_bytes()), write, indicate)]
    c2: External,
}

... where, inside rs-matter, I have:

pub const MATTER_BLE_SERVICE_UUID16: u16 = 0xFFF6;
pub const C1_CHARACTERISTIC_UUID: u128 = 0x18EE2EF5263D4559959F4F9C429F9D11;
pub const C2_CHARACTERISTIC_UUID: u128 = 0x18EE2EF5263D4559959F4F9C429F9D12;

With MATTER_BLE_SERVICE_UUID16 everything is great, because trouble's Uuid has impl From<u16> for Uuid.
With c1 and c2 life is not so great, because Uuid has neither impl From<[u8; 16]> for Uuid, nor impl From<u128> for Uuid.

Therefore, I have to use the explicit Uuid::Uuid128(C1_CHARACTERISTIC_UUID.to_be_bytes()).
However, since the proc-macro generated code does internally do .into() on my Uuid, Clippy then kicks-in with:

warning: useless conversion to the same type: `trouble_host::prelude::Uuid`
  --> src/ble.rs:45:29
   |
45 |     #[characteristic(uuid = Uuid::Uuid128(C1_CHARACTERISTIC_UUID.to_be_bytes()), write)]
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into()`: `Uuid::Uuid128(C1_CHARACTERISTIC_UUID.to_be_bytes())`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion
   = note: `#[warn(clippy::useless_conversion)]` on by default

I think we either need extra From<???> for Uuid impls, or this (and other) Clippy lints disabled in the proc-macros, or ideally both.

[lure23]

When making custom profiles, I think 128-bit UUID:s is the only way to go. Thus, really would like to have them supported and tested the same as 16-bit.

[jamessizeland]

Yep, makes sense, I can add that in too. So far I haven't because we support string literals for 128bit UUIDs and that's been enough for me so far.

But adding From is possible too, or we can add more types that impl Into<trouble_host::Uuid>

[ivmarkov]

I think adding From<[u8; 16]> and From<u128> would do for now.

[ivmarkov]

Perhaps also From<[u8; 2]> for symmetry.

[lure23]

One notion regarding this: _source

pub enum Uuid {
    Uuid16(u16),
    Uuid128([u8; 16]),
}

Is there a reason the source uses [u8; 16] and not u128 straight up? Since the latter is supported in Rust, wouldn't it be more aligned with the use of u16?

[jamessizeland]

I'm going to take a look at this now.