Ok, the problem is that you directly ignore the case when i[0] isn't nnkIdent.
When this happens you have to recursively find and replace the leftmost i[0]
node with obj.<what you found> e.g. in a.b.c you replace a with obj.a
so your code becomes
proc replaceBase(node: NimNode, obj: NimNode): NimNode =
# later
if i.kind == nnkAsgn:
let l = replaceBase(i[0], obj)
result.add(newAssignment(l, i[1]))
Run
Implementing replaceBase will resolve everything.
Again, this might look harder than the string replace, but for most macros you
need to manipulate nodes in a similar way, e.g. when you add X in call(args) ->
call(X, args) you can't just add repr-s until you get the result
