Bitfield derive panics when ty uses leading :: (e.g. ::core::ffi::c_uint) #1581
Description
When translating C bitfields, C2Rust generates #[bitfield(...)] attributes with type strings that use a leading ::, e.g.:
#[bitfield(name = "a", ty = "::core::ffi::c_uint", bits = "0..=2")]
However, with the supported toolchain combination (e.g. nightly-2022-08-08 and c2rust-bitfields-derive), this causes the BitfieldStruct derive macro to panic during expansion with:
proc-macro derive panicked
message: `""` is not a valid identifier
Changing the generated code to use a non–leading-:: type string (e.g. ty="c_uint") resolves the issue immediately.
Original C Program
#include <stdio.h>
int main(void) {
struct {
unsigned int a : 3;
unsigned int b : 5;
unsigned int c : 4;
int d : 6; /* signed bitfield */
} bf = {0};
bf.a = 5;
printf("Bitfield Test1: Input=5, Result=%u\n", bf.a);
return 0;
}
C2Rust-Generated Rust
#![allow(
dead_code,
non_camel_case_types,
non_snake_case,
non_upper_case_globals,
unused_assignments,
unused_mut
)]
extern "C" {
fn printf(__format: *const ::core::ffi::c_char, ...) -> ::core::ffi::c_int;
}
#[derive(Copy, Clone, BitfieldStruct)]
#[repr(C)]
pub struct C2RustUnnamed {
#[bitfield(name = "a", ty = "::core::ffi::c_uint", bits = "0..=2")]
#[bitfield(name = "b", ty = "::core::ffi::c_uint", bits = "3..=7")]
#[bitfield(name = "c", ty = "::core::ffi::c_uint", bits = "8..=11")]
#[bitfield(name = "d", ty = "::core::ffi::c_int", bits = "12..=17")]
pub a_b_c_d: [u8; 3],
#[bitfield(padding)]
pub c2rust_padding: [u8; 1],
}
unsafe fn main_0() -> ::core::ffi::c_int {
let mut bf: C2RustUnnamed = {
let mut init = C2RustUnnamed {
a_b_c_d: [0; 3],
c2rust_padding: [0; 1],
};
init.set_a(0 as ::core::ffi::c_uint);
init.set_b(0);
init.set_c(0);
init.set_d(0);
init
};
bf.set_a(5 as ::core::ffi::c_uint as ::core::ffi::c_uint);
printf(
b"Bitfield Test1: Input=5, Result=%u\n\0" as *const u8
as *const ::core::ffi::c_char,
bf.a() as ::core::ffi::c_int,
);
return 0 as ::core::ffi::c_int;
}
pub fn main() {
unsafe { ::std::process::exit(main_0() as i32) }
}
Environment
- c2rust version: v0.21.0
- rustc version: nightly-2022-08-08
- c2rust-bitfields：0.21.0
- proc-macro2：1.0.103
- quote：1.0.40
- syn：2.0.106
- platform：Ubuntu 24.04