Cannot find type '__BindgenOpaqueArray' in this scope

[dtolnay]

Repro:

cargo run --manifest-path bindgen-cli/Cargo.toml -- \
    --enable-cxx-namespaces \
    <(echo '
        namespace repro {
            template<unsigned int N> class Array { int inner[N]; };
            class C { Array<3> arr; };
        }
    ') \
    -- \
    -xc++ \
    | rustc --crate-type=lib --edition=2021 /dev/stdin

Bisects to #2880. @GKFX

This impacts Clang's implementation of #include <chrono>.

[dtolnay]

The generated code is:

#[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
pub mod root {
    #[doc = r" If Bindgen could only determine the size and alignment of a"]
    #[doc = r" type, it is represented like this."]
    #[derive(PartialEq, Copy, Clone, Debug, Hash)]
    #[repr(C)]
    pub struct __BindgenOpaqueArray<T: Copy, const N: usize>(pub [T; N]);
    impl<T: Copy + Default, const N: usize> Default for __BindgenOpaqueArray<T, N> {
        fn default() -> Self {
            Self([<T as Default>::default(); N])
        }
    }
    #[allow(unused_imports)]
    use self::super::root;
    pub mod repro {
        #[allow(unused_imports)]
        use self::super::super::root;
        #[repr(C)]
        #[derive(Debug, Copy, Clone)]
        pub struct C {
            pub arr: __BindgenOpaqueArray<u32, 3usize>,
        }
        #[allow(clippy::unnecessary_operation, clippy::identity_op)]
        const _: () = {
            ["Size of C"][::std::mem::size_of::<C>() - 12usize];
            ["Alignment of C"][::std::mem::align_of::<C>() - 4usize];
            ["Offset of field: C::arr"]
                [::std::mem::offset_of!(C, arr) - 0usize];
        };
    }
}

error[E0412]: cannot find type `__BindgenOpaqueArray` in this scope
  --> /dev/stdin:23:22
   |
23 |             pub arr: __BindgenOpaqueArray<u32, 3usize>,
   |                      ^^^^^^^^^^^^^^^^^^^^ not found in this scope
   |
help: consider importing this struct
   |
18 +         use crate::root::__BindgenOpaqueArray;
   |

[pvdrz]

@GKFX do you think you could take a look at this? it seems you have to import __BindgenOpaqueArray when using C++ namespaces

[GKFX]

@pvdrz I have opened a pull request for this at #3028.