struct FlashBool(u8); breaks zerocopy_derive::IntoBytes with "expected bool because of return type in this derive macro expansion"

[kairoswater-jason]

I've got a custom type called struct FlashBool(u8); that implements From<bool>, Into<bool>, and PartialEq<bool>

When I try to use it in another struct called DebugMode that derives the usual zerocopy traits, it produces the following error:

error[E0308]: mismatched types
  --> settings/debug_mode.rs:23:2
   |
19 |  #[derive(PartialEq, Copy, Clone, Debug, zerocopy_derive::FromBytes, zerocopy_derive::IntoBytes, zerocopy_derive::Immutable, zerocopy_der...
   |           ---------
   |           |
   |           expected `bool` because of return type
   |           in this derive macro expansion
...
23 |     pub debug_mode: FlashBool,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `FlashBool`

error[E0308]: mismatched types
  --> settings/debug_mode.rs:24:5
   |
19 |  #[derive(PartialEq, Copy, Clone, Debug, zerocopy_derive::FromBytes, zerocopy_derive::IntoBytes, zerocopy_derive::Immutable, zerocopy_der...
   |           ---------
   |           |
   |           expected `bool` because of return type
   |           in this derive macro expansion
...
24 |     pub modem_mute: FlashBool,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `FlashBool`

below is the full definition of FlashBool

#[derive(PartialEq, Copy, Clone, Debug, zerocopy_derive::FromBytes, zerocopy_derive::IntoBytes, zerocopy_derive::Immutable, zerocopy_derive::KnownLayout)]
#[repr(packed)]
pub struct DebugMode {
    pub debug_mode: FlashBool,
    pub modem_mute: FlashBool,
}

#[derive(Debug, Clone, Copy, zerocopy_derive::FromBytes, zerocopy_derive::IntoBytes, zerocopy_derive::Immutable, zerocopy_derive::KnownLayout)]
#[repr(packed)]
pub struct FlashBool(u8);
impl PartialEq<bool> for FlashBool {
    fn eq(&self, other: &bool) -> bool {
        *other == (*self).into()
    }
}

impl From<bool> for FlashBool {
    fn from(value: bool) -> Self {
        if value {
            Self(1)
        } else {
            Self(0)
        }
    }
}

impl Into<bool> for FlashBool {
    fn into(self) -> bool {
        let self_value = self.0 != 0;
        self_value
    }
}

Here are my questions:
(1) am I violating some rule or expectation that the derive proc macros have?
(2) is there some easy workaround, other than just using an u8 (instead of FlashBool) and casting it to a bool at some later time someplace else.

Is there some good way to have a type similar to FlashBool in my DebugMode struct? (previously I was using a plain u8 to represent a bool, but it was cumbersome)

additional information from my cargo.lock file:

 "zerocopy 0.8.26",
 "zerocopy-derive 0.8.26",

[kairoswater-jason]

After some digging, it looks like impl PartialEq<bool> is what broke it

I wrote this type because an external API requires FromBytes (rather than TryFromBytes), with precludes the use of bool. In this case a u8 where 0 is false and 1-255 is true is what is needed.

[joshlf]

Do you still think there's a zerocopy bug here? Ie, was the impl PartialEq<bool> the only issue, or do you think that impl PartialEq<bool> played badly with a zerocopy bug?

[kairoswater-jason]

I think it's a bug. I'd like to know your opinion.

I don't expect implementing PartialEq to have any effect on the ability to serialize the type.

The compiler error suggests that zeropcopy interpreted the type as if I supplied bool for the type rather than struct FlashBool(u8)

This seems unexpected to me.

Removing the partialEq implementation makes zerocopy behave normally, which in my mind futher solidifies the chance that this is not intended behavior by the maintainers. But I can only speculate

[joshlf]

Can you remove the zerocopy derives but keep the PartialEq implementation and the PartialEq derive? I suspect those may be interacting badly and zerocopy may be unrelated (but I could be wrong).

[jswrenn]

What's the interaction here with zerocopy? Shaving off some of the derives, this more minimal example has the same behavior: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=a6899726f32039339330f331a503f479

The problem is you haven't implemented PartialEq<FlashBool> for FlashBool.

[kairoswater-jason]

You are right, I was mistaken. It is not a zerocopy issue. Sorry for the confusion

Wrapping of a long line of text in the console placed the underline under one of the zerocopy derives. And I just assumed that I was looking in the correct spot, when I was looking the wrong place the entire time. I didn't event notice it when I copy and pasted the error here, where it renders correctly.