invalid type application returns instead of throwing

[nsajko]

julia> struct S{A, B<:AbstractVector{A}} end

julia> S{<:Any,Matrix}  # expected to throw, as `Matrix` doesn't subtype `AbstractVector`
S{<:Any, Matrix}

julia> S{<:Any,Matrix} <: S  # a paradox?
false

If the parameter constraint in the definition of struct S is relaxed (!) like below, the type application throws as expected:

julia> struct S{A, B<:AbstractVector} end

julia> S{<:Any,Matrix}
ERROR: TypeError: in S, in B, expected B<:(AbstractVector), got Type{Matrix}
Stacktrace:
 [1] top-level scope
   @ REPL[2]:1

This perhaps suggests a fix: when Julia sees a parameter constraint with a type application, it could consider as multiple type constraints, e.g., <:AbstractVector{A} could be internally interpreted as two constraints, <:AbstractVector{A} and <:AbstractVector. If you get what I mean.

[KristofferC]

Dup of #53380?

[vtjnash]

We could, but you potentially lose the ability to specify some type constraints in dispatch, so it may not be worthwhile to add the error, as it doesn't cause any issues to be permitted