close #16123 std/sets with closures in cpp (#17921)

* close #16123 std/sets with closures in cpp

* fixup

tests/sets/tsets_various.nim

@@ -1,15 +1,12 @@
 discard """
   targets: "c cpp js"
-  output: '''
-set is empty
-'''
 """
 
-
 import std/[sets, hashes]
 
 from std/sequtils import toSeq
 from std/algorithm import sorted
+from stdtest/testutils import whenVMorJs
 
 proc sortedPairs[T](t: T): auto = toSeq(t.pairs).sorted
 template sortedItems(t: untyped): untyped = sorted(toSeq(t))
@@ -23,10 +20,12 @@ block tsetpop:
     discard a.pop()
   doAssert len(a) == 0
 
+  var msg = ""
   try:
     echo a.pop()
   except KeyError as e:
-    echo e.msg
+    msg = e.msg
+  doAssert msg == "set is empty"
 
 
 
@@ -258,6 +257,7 @@ block: # test correctness after a number of inserts/deletes
 
 
 template main() =
+  # xxx move all tests inside this
   block:
     let a = {true, false}
     doAssert $a == "{false, true}"
@@ -273,6 +273,14 @@ template main() =
     doAssert $a == "{false}"
     doAssert a.len == 1
 
+  block: # bug #16123
+    whenVMorJs: discard
+    do:
+      type CallType = proc() {.closure.}
+      var setA = initHashSet[CallType]()
+      let foo = proc() = discard
+      setA.incl(foo)
+      doAssert setA.contains(foo)
 
 static: main()
 main()