Hrm, the new errors highlighted some code that seems to be broken

New issue: since `Table[A, B]` allocates its backing storage with
`newSeq[KeyValuePair[A, B]]`, it's no longer legal to create a table
with `not nil` types used as either keys or values.

lib/pure/ioselects/ioselectors_epoll.nim

@@ -502,8 +502,7 @@ proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
   let fdi = int(fd)
   s.checkFd(fdi)
-  if fdi in s:
-    result = s.fds[fdi].data
+  result = s.fds[fdi].data
 
 proc setData*[T](s: Selector[T], fd: SocketHandle|int, data: T): bool =
   let fdi = int(fd)

lib/pure/ioselects/ioselectors_kqueue.nim

@@ -600,8 +600,7 @@ proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
   let fdi = int(fd)
   s.checkFd(fdi)
-  if fdi in s:
-    result = s.fds[fdi].data
+  result = s.fds[fdi].data
 
 proc setData*[T](s: Selector[T], fd: SocketHandle|int, data: T): bool =
   let fdi = int(fd)

lib/pure/ioselects/ioselectors_select.nim

@@ -410,11 +410,17 @@ else:
     body
 
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
+  # The compiler needs this to prove that all code paths return a value
+  result = (cast[ptr T](0'u))[]
+
   s.withSelectLock():
     let fdi = int(fd)
     for i in 0..<FD_SETSIZE:
       if s.fds[i].ident == fdi:
-        return s.fds[i].data
+        result = s.fds[i].data
+        break
+
+  assert cast[uint](addr(result)) != 0
 
 proc setData*[T](s: Selector[T], fd: SocketHandle|int, data: T): bool =
   s.withSelectLock():