Return statement on assignment rhs should work or give better error message

[andreasnoack]

julia> __tmp1 = let
         a = 1
         a
       end
1

julia> __tmp1
1

julia> __tmp2 = let
         a = 1
         return a
       end
1

julia> __tmp2
ERROR: UndefVarError: __tmp2 not defined

I noticed this when trying to assign to a dict which gave

julia> d["a"] = let
        a = 1
        return a
       end
ERROR: syntax: ssavalue with no def

I don't know if it makes sense to allow return in a let block but if it doesn't then it would be great with a better error message.

[yuyichao]

It does work (edit: as intended). Dup of #30499

[JeffBezanson]

This shouldn't give ssavalue with no def.

[JeffBezanson]

Dup of #31238