Version 0.1.42 breaks code with #![deny(trivial_numeric_casts)]

[Pzixel]

Minimal reproducible example

Cargo.toml

[dependencies]
num = "0.1"
num-derive = "0.1"

main.rs

#![deny(trivial_numeric_casts)]
extern crate num;
#[macro_use]
extern crate num_derive;

#[derive(FromPrimitive)]
pub enum SomeEnum {
    A = 1
}

fn main() {

}

Error:

   Compiling hello_world_clion v0.1.0 (file:///C:/Users/Alex/Documents/Rust/hello_world_clion)
error: trivial numeric cast: `isize` as `isize`. Cast can be replaced by coercion, this might require type ascription or a temporary variable
 --> src\main.rs:6:10
  |
6 | #[derive(FromPrimitive)]
  |          ^^^^^^^^^^^^^
  |
note: lint level defined here
 --> src\main.rs:1:9
  |
1 | #![deny(trivial_numeric_casts)]
  |         ^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

Our project depends heavily on this deny attribute so disable it is a no-no. Currently we use num-derive = "=0.1.41" but I hope we can switch to higher version. Is seems to be an easy fix.

[cuviper]

Sure, we can probably just add #[allow(trivial_numeric_casts)] in the derived code. Care to send a PR?
(and make sure we test with that deny somewhere too)

[Pzixel]

This deny is useful so I think we may just tune the macro a bit, instead of a as Foo it could just generate let a_as_foo: Foo : a. And it's safer than allow directive.

[cuviper]

You're welcome to experiment with different approaches, of course.

[Pzixel]

Ok, I can try. However, I'm not really familiar with macros because I'm new in rust and I just wanted my code to compile 😄 , but the whole last month I'm just fixing issues one by one in my dependencies... And this one seems to be really hard. Any help about how can I debug macro or something? Because I have no idea how to do it.

[cuviper]

I went ahead and allowed the warning in #7, if you'd like to test it on your code. We can followup with a different approach if you figure out something better.

Debugging macros is kind of a pain. On nightly rustc, you can use rustc --pretty=expanded to see what gets derived. There's also -Ztrace-macros and -Zdebug-macros, but I think those are only for macro_rules!.