Struct that fully contains a signed integer causes clippy error.

[snakehand]

This struct produces a clippy error:

#[bitfield(u16)]
/// X axis output value
pub struct OutX{
#[bits(16)]
val: i16,
}

error: &-masking with zero
--> src/lib.rs:564:1
|
564 | #[bitfield(u16)]
| ^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#bad_bit_mask
= note: #[deny(clippy::bad_bit_mask)] on by default
= note: this error originates in the attribute macro bitfield (in Nightly builds, run with -Z macro-backtrace for more info)

I have debugged it and tracked it down to a debug assert, and propose this change that captures the same logic without causing errors in clippy:

index d0e0c39..669947b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -727,7 +727,7 @@ fn parse_field(attrs: &[syn::Attribute], ty: &syn::Type, ignore: bool) -> syn::R
// Bounds check and remove leading ones from negative values
ret.into = quote! {{
#[allow(unused_comparisons)]

•            debug_assert!(if this >= 0 { this & !#mask == 0 } else { !this & !#mask == 0 }, "value out of bounds");
  

•            debug_assert!(if this >= 0 { this | #mask == #mask } else { !(this | #mask) == 0 }, "value out of bounds");
             (this & #mask) as _
         }};
     }
  

[snakehand]

bitfield_err.zip

Minimal example

[wrenger]

Hi @snakehand, thanks for your PR. I'm currently traveling but I'll look into this as soon as I'm back next week.

Can you also tell me the rustc/Clippy version you are using?

[wrenger]

The bounds check was error-prone and has been fixed (as discussed in #24). This also resolves this issue.