Bug with methods of an inner function in different scopes

[simonster]

On 0.5/master, there seem to be conflicting assumptions somewhere regarding scope when different methods of inner functions have different scopes.

function outer()
    inner(x) = x
    let y = 1
        inner() = y
        inner
    end
end

julia> outer()
ERROR: UndefVarError: y not defined
 in outer() at ./REPL[1]:2

This doesn't seem to make much sense, since inner isn't even called. In fact, I get the error even if I wrap the let block in if false ... end.

On 0.4:

julia> outer()
inner (generic function with 2 methods)

and inner works as expected.

For fun, this works:

function outer()
    inner(x) = x
    let y = 1
        (::typeof(inner))() = y
        inner
    end
end

but it prints a warning about a rewritten method definition every time outer is called.

It may be that this code pattern is actually impossible to handle since #13412, but if that's the case, we could be more explicit about that.

[yuyichao]

Dup of #15602