Static REPR_C_ENUMS_LARGER_THAN_INT 

pub static REPR_C_ENUMS_LARGER_THAN_INT: &Lint

The repr_c_enums_larger_than_int lint detects repr(C) enums with discriminant values that do not fit into a C int or unsigned int.

Example

#[repr(C)]
enum E {
    V = 9223372036854775807, // i64::MAX
}

This will produce:

error: `repr(C)` enum discriminant does not fit into C `int` nor into C `unsigned int`
  --> $DIR/repr-c-big-discriminant1.rs:16:5
   |
LL |     A = 9223372036854775807, // i64::MAX
   |     ^
   |
   = note: `repr(C)` enums with big discriminants are non-portable, and their size in Rust might not match their size in C
   = help: use `repr($int_ty)` instead to explicitly set the size of this enum

Explanation

In C, enums with discriminants that do not all fit into an int or all fit into an unsigned int are a portability hazard: such enums are only permitted since C23, and not supported e.g. by MSVC.

Furthermore, Rust interprets the discriminant values of repr(C) enums as expressions of type isize. This makes it impossible to implement the C23 behavior of enums where the enum discriminants have no predefined type and instead the enum uses a type large enough to hold all discriminants.

Therefore, repr(C) enums in Rust require that either all discriminants to fit into a C int or they all fit into an unsigned int.