rustdoc leaks `ident` macro meta-variables in non-literal const exprs in assoc tys & impl trait refs (excl. self ty)

Minimal reproduction:

pub struct S<const A: bool>;

pub const TRUE: bool = true;

macro_rules! example {
    ($unexpanded:ident) => {
        impl core::ops::Add<S<$unexpanded>> for S<$unexpanded> {
            type Output = S<$unexpanded>;

            fn add(self, _: S<$unexpanded>) -> Self::Output {
                S::<$unexpanded>
            }
        }
    };
}

example!(TRUE);

When I generate documentation for this with cargo doc, the documentation for S's trait implementations says

impl Add<S<$unexpanded>> for S<TRUE>
type Output = S<$unexpanded>

I expected the documentation to document the expanded code. It happens with both 1.79 and nightly.

The problem persists if I change the macro to put {} around $unexpanded, but then if I pass true instead of TRUE to the macro, it's expanded and shown as impl Add for S<{ true }> and type Output = S<true> (without the {})

% rustc --version --verbose
rustc 1.79.0 (129f3b996 2024-06-10)
binary: rustc
commit-hash: 129f3b9964af4d4a709d1383930ade12dfe7c081
commit-date: 2024-06-10
host: aarch64-apple-darwin
release: 1.79.0
LLVM version: 18.1.7

% rustc +nightly --version --verbose
rustc 1.81.0-nightly (8337ba918 2024-06-12)
binary: rustc
commit-hash: 8337ba9189de188e2ed417018af2bf17a57d51ac
commit-date: 2024-06-12
host: aarch64-apple-darwin
release: 1.81.0-nightly
LLVM version: 18.1.7

Start by reproducing the minimal macro example with cargo doc on the reported stable and nightly versions, then inspect the generated documentation for the Add implementation and associated Output type. Trace how rustdoc handles macro meta-variables in non-literal const expressions and impl trait references. Done means the generated documentation shows the expanded code rather than $unexpanded.