Return type assertions don't work with anonymous functions.

[Ismael-VC]

Anonymous functions don't accept return type assertions:

julia> (((x::T, y::T)::T) where {T<:Int}) -> x + y                   
ERROR: syntax: "(x::T,y::T)" is not a valid function argument name   

julia> function (((x::T, y::T)::T) where {T<:Int}); return x + y; end
ERROR: syntax: expected "(" in function definition

But this work:

julia> ((foo(x::T, y::T)::T) where {T<:Int}) = x + y                    
foo (generic function with 1 method)                                    

julia> function ((foo(x::T, y::T)::T) where {T<:Int}); return x + y; end
foo (generic function with 1 method)

[mauro3]

Dup of #23072

(Also, note that it is a return type conversion, not assertion.)

[Ismael-VC]

Thanks for correcting the terminology.