bug in closure capture boxing logic

[uniment]

Notice that foo() returns 3.

julia> VERSION
v"1.9.0-beta4"

julia> foo=let j=0, f, i
           while j < 3
               i = j + 1
               println("i == ", i)
               if j==0;  f = ()->i  end
               j += 1
           end
           i
           f
       end;
i == 1
i == 2
i == 3

julia> foo()
3

Comment out the line that says i, and foo() instead returns 1 (and its capture is not in a Core.Box anymore).

(ref: Discourse thread)

[uniment]

Worth noting that this was first observed using @goto:

julia> baz = let j=0
           @label upper
           i = j + 1
           println("i == ", i)
           if j != 0; @goto lower end
           f = ()->i
           @label lower
           j += 1
           if j < 3; @goto upper end
           #i
           f
       end;
i == 1
i == 2
i == 3

julia> baz()
1

[simeonschaub]

3 is the correct answer here, since the binding i exists outside the scope of the while loop as well. What I'm slightly surprised by is that let i; ... end is not enough to make i an outer binding if you comment out the i line.