Question: Is it possible to set a name for anonymous unions using an annotation comment to the C/C++ source code?

[leinardi]

I would like to know if is possible to suggest to bindgen a name for anonymous unions.

For example, if I have this structure:

typedef struct
{
	unsigned int	tCL;
	union {
	unsigned int	tRCD;
	unsigned int	tRCD_RD;
	};
	unsigned int	tRCD_WR,
			tRP,
			tRAS,
			tRC,

			tRCPB,
			tRPPB;
	union {
	unsigned int	tRRD;
	unsigned int	tRRDS;
	};
	unsigned int	tRRDL,
			tRRDDLR,

			tFAW,
			tFAWSLR,
			tFAWDLR,

			tWTRS,
			tWTRL,
			tWR;
} RAM_TIMING;

bindgen generates a rust struct like this:

#[repr(C)]
#[derive(Copy, Clone)]
pub struct RAM_TIMING {
    pub tCL: ::std::os::raw::c_uint,
    pub __bindgen_anon_1: RAM_TIMING__bindgen_ty_1,
    pub tRCD_WR: ::std::os::raw::c_uint,
    pub tRP: ::std::os::raw::c_uint,
    pub tRAS: ::std::os::raw::c_uint,
    pub tRC: ::std::os::raw::c_uint,
    pub tRCPB: ::std::os::raw::c_uint,
    pub tRPPB: ::std::os::raw::c_uint,
    pub __bindgen_anon_2: RAM_TIMING__bindgen_ty_2,
    pub tRRDL: ::std::os::raw::c_uint,
    pub tRRDDLR: ::std::os::raw::c_uint,
    pub tFAW: ::std::os::raw::c_uint,
    pub tFAWSLR: ::std::os::raw::c_uint,
    pub tFAWDLR: ::std::os::raw::c_uint,
    pub tWTRS: ::std::os::raw::c_uint,
    pub tWTRL: ::std::os::raw::c_uint,
    pub tWR: ::std::os::raw::c_uint
}

I was wondering if there is a way to specify a name for all the anonymous fiels, like __bindgen_anon_1 and RAM_TIMING__bindgen_ty_1.

I don't know if it makes sense, but I was hoping to be able to do something like:

typedef struct
{
	unsigned int	tCL;
        /// <div rustbindgen name="tRCD_u"></div>
	union {
	unsigned int	tRCD;
	unsigned int	tRCD_RD;
	};
[...]

to generate something like this:

#[repr(C)]
#[derive(Copy, Clone)]
pub struct RAM_TIMING {
    pub tCL: ::std::os::raw::c_uint,
    pub tRCD_u: RAM_TIMING__tRCD_u,
[...]

Unfortunately I cannot simply give a name to the union. If the comment solution is not possible, is there any other way to control the name used by the generated code in case of anonymous unions?

[emilio]

I don't think this is possible right now, but an annotation might be reasonable. What's the usecases for having the union be named? It cant' be named on C either.

[leinardi]

Hi @emilio, thank you for the answer. What I would like to achieve is to be able to pick a name for the __bindgen_anon_* fields.

Having several __bindgen_anon_* makes pretty hard to understand what are they actually mapping and I would love to be able to decide that name directly form the C header file with an annotation.

I would like to go from the current situation:

#[repr(C)]
#[derive(Copy, Clone)]
pub struct RAM_TIMING {
    pub tCL: ::std::os::raw::c_uint,
    pub __bindgen_anon_1: RAM_TIMING__bindgen_ty_1,
[...]

to something like this:

#[repr(C)]
#[derive(Copy, Clone)]
pub struct RAM_TIMING {
    pub tCL: ::std::os::raw::c_uint,
    pub tRCD_u: RAM_TIMING__tRCD_u,
[...]

I would like to have a way to decide the name of __bindgen_anon_1 and RAM_TIMING__bindgen_ty_1 so that, when I'm accessing this struct I could have self explanatory names instead of __bindgen_anon_*:

fn get_trct(ram_timing: &RAM_TIMING) -> u32 {
    ram_timing.tRCD_u.tRCD
}

instead of:

fn get_trct(ram_timing: &RAM_TIMING) -> u32 {
    ram_timing.__bindgen_anon_1.tRCD
}

[emilio]

Ok, so there are two things that have automatic names right now, one of them is __bindgen_anon, the other one is the union name itself (RAM_TIMING__bindgen_ty_1). I think an annotation for these seems fine. Do you envision a use case for the two names to be different? If not it can probably be the same annotation.

[leinardi]

Mmm, right now I can't think of a use case where where can be useful having different names so I would say to use the same annotation for both 👍 Thanks a lot!

[leinardi]

Ah, I forgot to say it: could this annotation work also for anonymous struct the same way that works for the unions?

The use case is something like this:

typedef union
{
	signed long long	Proc;
	struct {
		unsigned int	Core;
		signed int	Thread;
	};
} SERVICE_PROC;

that currently generate this:

#[repr(C)]
#[derive(Copy, Clone)]
pub union SERVICE_PROC {
    pub Proc: ::std::os::raw::c_longlong,
    pub __bindgen_anon_1: SERVICE_PROC__bindgen_ty_1,
    _bindgen_union_align: u64,
}

I would like to be able to choose the name of the anonymous struct the same way I could set the name of an anonymous union.

[noahgibbs]

Randomly: right now I'm hitting an annoyance that this would solve. Specifically, I'm marking a particular struct as blocklist and opaque. But its anonymous substructure is still being generated, which pulls in a lot of other types we don't want/need bindings for.

Naming the substructure would let us exclude it without hardcoding the bindgen automatic name as blocked/opaque. Hardcoding the automatically-generated name feels fragile.