results: work around void member codegen issue (#150)

stew/results.nim

@@ -304,11 +304,35 @@ type
     ## https://github.com/nim-lang/Nim/issues/13879 - double-zero-init slow
     ## https://github.com/nim-lang/Nim/issues/14318 - generic error raises pragma
 
-    case o: bool
-    of false:
-      e: E
-    of true:
-      v: T
+    # TODO https://github.com/nim-lang/Nim/issues/20699
+    # case o: bool
+    # of false:
+    #   e: E
+    # of true:
+    #   v: T
+
+    when T is void:
+      when E is void:
+        o: bool
+      else:
+        case o: bool
+        of false:
+          e: E
+        of true:
+          discard
+    else:
+      when E is void:
+        case o: bool
+        of false:
+          discard
+        of true:
+          v: T
+      else:
+        case o: bool
+        of false:
+          e: E
+        of true:
+          v: T
 
   Opt*[T] = Result[T, void]
 

tests/test_results.nim

@@ -403,3 +403,15 @@ block: # Experiments
     counter2 += 1
 
   doAssert counter2 == 1, "one-item collection when set"
+
+block: # Constants
+  # TODO https://github.com/nim-lang/Nim/issues/20699
+  type
+    WithOpt = object
+      opt: Opt[int]
+  const
+    noneWithOpt =
+      WithOpt(opt: Opt.none(int))
+  proc checkIt(v: WithOpt) =
+    doAssert v.opt.isNone()
+  checkIt(noneWithOpt)