fix results compiletime regression (#203)

* fix results compiletime regression

* disable results.value compiletime test for pre 1.6 nim

stew/results.nim

@@ -801,7 +801,10 @@ func value*[T, E](self: Result[T, E]): T {.inline.} =
   ## See also: Option.get
   withAssertOk(self):
     when T isnot void:
-      self.vResultPrivate
+      # TODO: remove result usage.
+      # A workaround for nim VM bug:
+      # https://github.com/nim-lang/Nim/issues/22216
+      result = self.vResultPrivate
 
 func value*[T: not void, E](self: var Result[T, E]): var T {.inline.} =
   ## Fetch value of result if set, or raise Defect

tests/test_results.nim

@@ -504,3 +504,29 @@ block: # Constants
     doAssert c == [1] and d == [2]
     let (e, f) = v.unsafeGet()
     doAssert e == [1] and f == [2]
+
+block:
+  # withAssertOk evaluated as statement instead of expr
+  # https://github.com/nim-lang/Nim/issues/22216
+  func bug(): Result[uint16, string] =
+    ok(1234)
+
+  const
+    x = bug()
+    y = x.value()
+
+  doAssert y == 1234
+
+  when (NimMajor, NimMinor) >= (1,6):
+    # pre 1.6 nim vm have worse bug
+    static:
+      var z = bug()
+      z.value() = 15
+      let w = z.get()
+      doAssert w == 15
+  
+  let
+    xx = bug()
+    yy = x.value()
+
+  doAssert yy == 1234