Failed to generate `Default` impl for arrays larger than 32 entries about rust-bindgen HOT 8 OPEN

Which rust version are you using? We have code to deal with this, see a380678

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Ah, so I couldn't repro this, but that's because for some reason --target=x86_64-pc-win32 is needed to repro:

./target/debug/bindgen --with-derive-default t.h -- --target=x86_64-pc-win32

Is the command I used to reproduce. It seems the MONITORINFO; line is kind of like a member, but it's unnamed and clang doesn't expose it as such... o.O

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And somehow that only happens when targeting windows

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I think that limitation in rustc is mostly historical? rust-lang/rust#124163 removes it.

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@emilio

Which rust version are you using? We have code to deal with this, see a380678

I'm able to repro on latest stable(stable-x86_64-pc-windows-msvc unchanged - rustc 1.77.2 (25ef9e3d8 2024-04-09)), beta(beta-x86_64-pc-windows-msvc updated - rustc 1.78.0-beta.7 (6fd191292 2024-04-12) (from rustc 1.78.0-beta.5 (9eff51035 2024-04-06))), and nightly(nightly-x86_64-pc-windows-msvc updated - rustc 1.79.0-nightly (e3181b091 2024-04-18) (from rustc 1.79.0-nightly (8b2459c1f 2024-04-09))). I'm assuming this is some sort of regression.

Ah, so I couldn't repro this, but that's because for some reason --target=x86_64-pc-win32 is needed to repro:

I am using x64 windows w/ msvc toolchain, so my native target is x86_64-pc-windows-msvc

I've also tried enabling clang's msvc compat, and it doesn't alter behavior here:

.clang_args([
            "-fms-compatibility",
            "-fms-extensions",
            "-fdelayed-template-parsing",
        ])

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@emilio looks like your proposed patch to rust was rejected. Can this continue to be handled by bindgen?

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I think this issue is a bit deeper than just a missing Default implementation. If we had something like this:

// hello.c
typedef struct bar {
  int *a[17];
} bar;

typedef struct foo {
  bar;
  int b;
} foo;

and ran bindgen hello.c --with-derive-default --no-layout-tests -- --target=x86_64-pc-windows-mvsc -fms-extensions you'd get:

/* automatically generated by rust-bindgen 0.69.4 */

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct bar {
    pub a: [*mut ::std::os::raw::c_int; 17usize],
}
impl Default for bar {
    fn default() -> Self {
        let mut s = ::std::mem::MaybeUninit::<Self>::uninit();
        unsafe {
            ::std::ptr::write_bytes(s.as_mut_ptr(), 0, 1);
            s.assume_init()
        }
    }
}
#[repr(C)]
#[repr(align(8))]
#[derive(Debug, Default, Copy, Clone)]
pub struct foo {
    pub __bindgen_padding_0: [u32; 34usize],
    pub b: ::std::os::raw::c_int,
}

implementing Default for foo is most likely wrong as you'd end up with an array of null pointers. I guess this is just a symptom of clang exposing the anonymous struct inside foo as an opaque type instead of giving the proper information.

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bruh

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