Support binding closure iterators (except on Nim == 2.0)

See nim-lang/Nim#22932.

questionable/binding.nim

@@ -2,12 +2,17 @@ import std/options
 import std/macros
 import ./private/binderror
 
+when (NimMajor, NimMinor) < (1, 1):
+  type SomePointer = ref | ptr | pointer
+elif (NimMajor, NimMinor) == (2, 0): # Broken in 2.0.0, fixed in 2.1.1.
+  type SomePointer = ref | ptr | pointer | proc
+else:
+  type SomePointer = ref | ptr | pointer | proc | iterator {.closure.}
+
 template toOption[T](option: Option[T]): Option[T] =
   option
 
-template toOption[T: ref | ptr | pointer | proc](value: T): Option[T] =
-  # `std/options` don't consider closure iterators to be pointer types
-  # (probably a bug) so we don't list them here.
+template toOption[T: SomePointer](value: T): Option[T] =
   value.option
 
 proc placeholder(T: type): T =

testmodules/options/test.nim

@@ -187,6 +187,18 @@ suite "optionals":
     if a =? p:
       fail
 
+    when (NimMajor, NimMinor) >= (1, 1) and (NimMajor, NimMinor) != (2, 0):
+      var it = iterator: int = yield 2
+      if a =? it:
+        for x in a:
+          check x == 2
+      else:
+        fail
+
+      it = nil
+      if a =? it:
+        fail
+
   test "=? rejects non-reference types":
     check `not` compiles do:
       if a =? 0: