make 'not nil' experimental

tests/notnil/tmust_compile.nim

@@ -3,6 +3,7 @@ discard """
 """
 
 # bug #6682
+{.experimental: "notnil".}
 
 type
     Fields = enum

tests/notnil/tnotnil.nim

@@ -2,7 +2,7 @@ discard """
   line: 22
   errormsg: "type mismatch"
 """
-
+{.experimental: "notnil".}
 type
   PObj = ref TObj not nil
   TObj = object
@@ -15,8 +15,8 @@ type
 proc p(x: string not nil): int =
   result = 45
 
-proc q(x: MyString) = nil
-proc q2(x: string) = nil
+proc q(x: MyString) = discard
+proc q2(x: string) = discard
 
 q2(nil)
 q(nil)

tests/notnil/tnotnil1.nim

@@ -4,7 +4,7 @@ discard """
 """
 
 import strutils
-
+{.experimental: "notnil".}
 
 type
   TObj = object
@@ -18,13 +18,13 @@ proc q(s: superstring) =
   echo s
 
 proc p2() =
-  var  a: string = "I am not nil"
+  var a: string = "I am not nil"
   q(a) # but this should and does not
 
 p2()
 
 proc q(x: pointer not nil) =
-  nil
+  discard
 
 proc p() =
   var x: pointer

tests/notnil/tnotnil2.nim

@@ -4,7 +4,7 @@ discard """
 """
 
 import strutils
-
+{.experimental: "notnil".}
 
 type
   TObj = object

tests/notnil/tnotnil3.nim

@@ -5,7 +5,7 @@ discard """
 
 # bug #584
 # Testprogram for 'not nil' check
-
+{.experimental: "notnil".}
 const testWithResult = true
 
 type

tests/notnil/tnotnil4.nim

@@ -2,6 +2,8 @@ discard ""
 type
    TObj = ref object
 
+{.experimental: "notnil".}
+
 proc check(a: TObj not nil) =
   echo repr(a)
 

tests/notnil/tnotnil_in_generic.nim

@@ -3,6 +3,7 @@ discard """
 """
 
 # bug #2216
+{.experimental: "notnil".}
 
 type
     A[T] = ref object

tests/notnil/tnotnil_in_objconstr.nim

@@ -2,7 +2,7 @@ discard """
   errormsg: "fields not initialized: bar"
   line: "13"
 """
-
+{.experimental: "notnil".}
 # bug #2355
 type
   Foo = object