Use of $crate in macro patterns is questionable

[CAD97]

See rust-lang/rust#99447 (comment)

The fact that $crate in the macro_rules LHS is accepted and glued into kw::DollarCrate is likely an accidental bug. The single use is an internal macro helper arm,

ndarray/src/slice.rs

Line 845 in f8522cf

(@parse ::core::marker::PhantomData::<$crate::Ix0>, ::core::marker::PhantomData::<$crate::Ix0>, []) => {

which looking at the macro, should probably be written to take $in_dim:expr, $out_dim:expr, like the other arms anyway.