implement RFCs/294 ; disallow enum <=> enum conversion (#16351)

* fix https://github.com/nim-lang/RFCs/issues/294 ; disallow enum <=> enum conversion
* fix the runnableExamples that was the instigator of this RFC
* legacy -d:nimLegacyConvEnumEnum
* use -d:nimLegacyConvEnumEnum in important_package nimgame2
* add test for enum cast
* improve changelog
* add changelog: Changes affecting backward compatibility
* cleanup changelog
* fix changelog

2 files changed, 63 insertions, 6 deletions

diff --git a/tests/misc/tcast.nim b/tests/misc/tcast.nim
index 454801a2d..6d67b1c52 100644
--- a/tests/misc/tcast.nim
+++ b/tests/misc/tcast.nim
@@ -48,7 +48,7 @@ block:
   var x: ref int = nil
   doAssert cast[int](cast[ptr int](x)) == 0
 
-block:
+block: # cast of nil
   block:
     static:
       let a = cast[pointer](nil)
@@ -71,7 +71,33 @@ block:
     static:
       doAssert cast[RootRef](nil).repr == "nil"
 
-  # Issue #15730, not fixed yet
-  # block:
-  #   static:
-  #     doAssert cast[cstring](nil).repr == "nil"
+  when false: # xxx bug #15730, not fixed yet
+    block:
+      static:
+        doAssert cast[cstring](nil).repr == "nil"
+
+template main() =
+  # xxx move all under here to get tested in VM
+  block: # cast of enum
+    type Koo = enum k1, k2
+    type Goo = enum g1, g2
+    type Boo = enum b1 = -1, b2, b3, b4
+    type Coo = enum c1 = -1i8, c2, c3, c4
+    when nimvm:
+      # xxx: Error: VM does not support 'cast' from tyEnum to tyEnum
+      discard
+    else:
+      doAssert cast[Koo](k2) == k2
+      doAssert cast[Goo](k2) == g2
+      doAssert cast[Goo](k2.ord) == g2
+
+      doAssert b3.ord == 1
+      doAssert cast[Koo](b3) == k2
+      doAssert cast[Boo](k2) == b3
+
+      doAssert c3.ord == 1
+      doAssert cast[Koo](c3) == k2
+      doAssert cast[Coo](k2) == c3
+
+static: main()
+main()
diff --git a/tests/misc/tconv.nim b/tests/misc/tconv.nim
index f7d15b0b5..c93fc57f8 100644
--- a/tests/misc/tconv.nim
+++ b/tests/misc/tconv.nim
@@ -1,5 +1,13 @@
+discard """
+  nimout:'''
+tconv.nim(81, 15) Warning: enum to enum conversion is now deprecated [User]
+'''
+"""
+
 template reject(x) =
-    static: assert(not compiles(x))
+  static: doAssert(not compiles(x))
+template accept(x) =
+  static: doAssert(compiles(x))
 
 reject:
     const x = int8(300)
@@ -55,3 +63,26 @@ block: # issue 3766
     proc r(x: static[R]) =
       echo x
     r 3.R
+
+
+block: # https://github.com/nim-lang/RFCs/issues/294
+  type Koo = enum k1, k2
+  type Goo = enum g1, g2
+
+  accept: Koo(k2)
+  accept: k2.Koo
+  accept: k2.int.Goo
+
+  reject: Goo(k2)
+  reject: k2.Goo
+  reject: k2.string
+
+  {.define(nimLegacyConvEnumEnum).}
+  discard Goo(k2)
+  accept: Goo(k2)
+  accept: k2.Goo
+  reject: k2.string
+  {.undef(nimLegacyConvEnumEnum).}
+
+  reject: Goo(k2)
+  reject: k2.Goo