Attempts at more terse `fixint` opt-ins

[pwfff]

Two standalone commits here:

1. An attempt at just making the field attribute a bit more terse, but I think this is basically just the 'wrapper' y'all had before? Still have to annotate every field, plus now I have to use into() everywhere. Diff for my project looks like this:

   diff --git a/device/src/messaging/packets.rs b/device/src/messaging/packets.rs
   index 0d22758..02c80ab 100644
   --- a/device/src/messaging/packets.rs
   +++ b/device/src/messaging/packets.rs
   @@ -1,4 +1,5 @@
   use arrayref::array_ref;
   +use postcard::fixint::*;
   use serde::{Deserialize, Serialize};
   
   use super::wrapper::MAX_MESSAGE_SIZE;
   @@ -34,10 +35,8 @@ pub struct RequestControllerCount {}
   
   #[derive(Serialize, Deserialize, Debug, Eq, PartialEq)]
   pub struct RequestControllerCountResponse {
   -    #[serde(with = "postcard::fixint::le")]
   -    packet_id: u32,
   -    #[serde(with = "postcard::fixint::le")]
   -    controller_count: u32,
   +    packet_id: LE<u32>,
   +    controller_count: LE<u32>,
   }
   
   impl Handler<RequestControllerCountResponse> for RequestControllerCount {
   @@ -48,8 +47,8 @@ impl Handler<RequestControllerCountResponse> for RequestControllerCount {
   
    fn handle(&self, controller: &Controller) -> RequestControllerCountResponse {
        RequestControllerCountResponse {
   -            packet_id: 0,
   -            controller_count: controller.controller_count(),
   +            packet_id: 0.into(),
   +            controller_count: controller.controller_count().into(),
        }
    }
   }

2. A macro based on this post I found: https://users.rust-lang.org/t/proc-macro-attribute-to-add-a-serde-deserialize-with-to-every-field-in-a-struct/71231 This seems... fragile. I did find a serde issue/PR where they wanted to do something similar, but it's old, not very active, and had a lot of feedback I didn't quite grok. This does manage to achieve exactly what I was looking for though, so I have a copy in my own codebase that I'm proceeding with. Changes to my project look like this:

   
   diff --git a/device/src/messaging/packets.rs b/device/src/messaging/packets.rs
   index 02c80ab..b7bdeb9 100644
   --- a/device/src/messaging/packets.rs
   +++ b/device/src/messaging/packets.rs
   @@ -1,5 +1,5 @@
   use arrayref::array_ref;
   -use postcard::fixint::*;
   +use corsairust_macros::all_fields_with;
   use serde::{Deserialize, Serialize};
   
   use super::wrapper::MAX_MESSAGE_SIZE;
   @@ -33,10 +33,11 @@ pub trait Handler<R: Serialize> {
   
   pub struct RequestControllerCount {}

+#[all_fields_with("postcard::fixint::le")]

[derive(Serialize, Deserialize, Debug, Eq, PartialEq)]

pub struct RequestControllerCountResponse {

• packet_id: LE,
• controller_count: LE,
• packet_id: u32,

• controller_count: u32, }

  impl Handler for RequestControllerCount { @@ -47,8 +48,8 @@ impl Handler for RequestControllerCount {

  fn handle(&self, controller: &Controller) -> RequestControllerCountResponse { RequestControllerCountResponse {

• packet_id: 0.into(),
• controller_count: controller.controller_count().into(),
• packet_id: 0,
• controller_count: controller.controller_count(), } } }

There's probably a better way to make this stuff happen at the library level? Like ideally use postcard::fixint::le::* would just magically configure it for your whole module, but that magic is beyond me still :smiling_face_with_tear:

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[pwfff]

Oh, and this is re: https://github.com/jamesmunns/postcard/issues/95