Exporting a `rustc_macro_transparency = "opaque"` macro from `std` spams `missing stability attribute` errors

I tried this code:

// inside any publicly visible module of `std`
// (not `core` or `alloc`)

#[doc(hidden)] // or any docs you want
#[unstable(feature = "foobar", issue = "none")] // or any stability you want
pub macro foo {() => {},}

I expected to see this happen: It compiles

Instead, this happened: 934 instances of error: ... has missing stability attribute, from items all over std

Meta

stage1 build of 15283f6fe95e5b604273d13a428bab5fc0788f5a (./x build library/std)

@rustbot label requires-nightly requires-internal-features F-staged_api F-decl_macro A-decl-macros-2-0 T-compiler A-hygiene

Reproduce the issue by adding the shown macro to a publicly visible module in std and running the stage1 build command, ./x build library/std. Then trace the stability checking involved in exporting the opaque macro. Done means the std build completes without the reported missing stability attribute errors.