fix #20023 hash for generic tables (#20346)

* fix #20023 hash for generic tables

* use default computation

* Update lib/pure/collections/tables.nim

Co-authored-by: Dan Rose <dan@digilabs.io>

* Update lib/pure/collections/tables.nim

Co-authored-by: Dan Rose <dan@digilabs.io>

* Update lib/pure/collections/tables.nim

* Update lib/pure/collections/tables.nim

* Update t20023.nim

---------

Co-authored-by: Dan Rose <dan@digilabs.io>
Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

lib/pure/collections/tables.nim

@@ -2901,3 +2901,18 @@ iterator mvalues*[A](t: CountTableRef[A]): var int =
     if t.data[h].val != 0:
       yield t.data[h].val
       assert(len(t) == L, "the length of the table changed while iterating over it")
+
+proc hash*[K,V](s: Table[K,V]): Hash =
+  for p in pairs(s):
+    result = result xor hash(p)
+  result = !$result
+
+proc hash*[K,V](s: OrderedTable[K,V]): Hash =
+  for p in pairs(s):
+    result = result !& hash(p)
+  result = !$result
+
+proc hash*[V](s: CountTable[V]): Hash =
+  for p in pairs(s):
+    result = result xor hash(p)
+  result = !$result

tests/stdlib/t20023.nim

@@ -0,0 +1,10 @@
+import std/[tables, hashes, assertions]
+
+
+let t = ()
+var a = toTable({t:t})
+del(a,t)
+let b = default(typeof(a))
+
+doAssert a==b , "tables are not equal"
+doAssert hash(a) == hash(b), "table hashes are not equal"