--use-core bindings refers std

[pepyakin]

Input C/C++ Header

// bindgen-flags: --impl-debug --use-core --raw-line "extern crate core;"

class C {
    bool a: 1;
    bool b: 7;
    int large_array[50];
};

Bindgen Invocation

See bindgen-flags above

Actual Results

// ... stripped

extern crate core;

#[repr(C)]
#[derive(Copy)]
pub struct C {
    pub _bitfield_1: u8,
    pub large_array: [::std::os::raw::c_int; 50usize]
}

// stripped ...

Expected Results

Despite that --use-core flag is provided large_array field having a type which refers std.
I expect that either error is printed stating that bindings couldn't be generated with --use-core or bindings which don't use std generated.

[fitzgen]

Nice catch!

I expect the fix for this is really easy (just forgetting to look at the prefix and emitting std regardless somewhere in src/codegen/mod.rs), but I hesitate marking it E-easy without being able to add clear instructions on how to fix this. Needs a little bit of investigation, so marking it E-less-easy.

[emilio]

This is working as expected, --use-core doesn't replace std, since it doesn't include them. You need to manually point to somewhere, e.g., libc, using --ctypes-prefix.

Worth pointing it out in the FAQ or something though, I guess.

[joshlf]

To clarify: The issue is that some types are present in std and not in core, and thus --use-core has to still rely on std for those types? Would it be feasible to add the offending types to core to fix this problem?

[emilio]

Either that, or using the --ctypes-prefix option, which is meant just for that. I'm not sure the c_* types are meant to be in core.

[emilio]

Closing per #1015 (comment), since as things stand ctypes-prefix should be used. If rust puts the ctypes in core, then another issue can be opened to make bindgen adapt to that.

[joshlf]

If these types aren't in core, what would we pass to ctypes-prefix?

Also, I've asked about moving them to core.

[emilio]

You should pass, e.g., libc, to use the libc crate, or a module / crate of your own that defines the needed types for the target architecture.

Though usually you'd want libc, I suspect.

[coffeenotfound]

The description of --use-core is "Use types from Rust core instead of std."
If it doesn't do that how in gods name is it "working as intended". What does it do?

[emilio]

Well, there is not (or didn't use to be at least) any alternative for std::os::raw::c_* types in core, so it's not clear to me what output do you expect?

We provide an option to not use std types for those and use a crate or module of your choice. Maybe the description should include "when possible" or something.