property destructuring doesn't allow lhs-type-declaration

[aviatesk]

#39285 implements the property destructuring syntax, but it doesn't allows us to declare types of destructured locals.

julia> struct Foo{T<:Integer}
           a::T
       end
       
julia> code_typed((Foo,); optimize = false) do foo
           (; a::Int) = foo
       end
ERROR: syntax: invalid assignment location "(; a::Int,)" around REPL[5]:2
Stacktrace:
[1] top-level scope
  @ REPL[5]:1

# works
julia> code_typed((Foo,); optimize = false) do foo
           a::Int = foo.a
       end
1-element Vector{Any}:
 CodeInfo(
1 ─ %1 = Base.getproperty(foo, :a)::Integer
│   %2 = Base.convert(Main.Int, %1)::Int64
│        (a = Core.typeassert(%2, Main.Int))::Int64
└──      return %1
) => Integer

Can this be fixed ?
/cc @simeonschaub

[simeonschaub]

Yes, I think we can just allow that one.

[simeonschaub]

I guess the only concern would be that if used in a function declaration, people might assume that this type annotations could be used for dispatch as well.

[aviatesk]

We can just throw that case, as we do for tuple destructuring ?

julia> function foo((a::Int, b::Int))
           a + b
       end
ERROR: syntax: invalid argument destructuring syntax "(a::Int, b::Int)"
Stacktrace:
 [1] top-level scope
   @ none:1

[simeonschaub]

Ah, that's true.