results: fix `catch` template for statements (#201)

* results: fix `catch` template for statements

* disable void catch tests on pre-1.6

stew/results.nim

@@ -731,7 +731,11 @@ template catch*(body: typed): Result[type(body), ref CatchableError] =
   type R = Result[type(body), ref CatchableError]
 
   try:
-    R.ok(body)
+    when type(body) is void:
+      body
+      R.ok()
+    else:
+      R.ok(body)
   except CatchableError as eResultPrivate:
     R.err(eResultPrivate)
 

tests/test_results.nim

@@ -89,12 +89,21 @@ block:
   doAssert rOkV == $rOk.get()
 
   # Exceptions -> results
-  func raises(): int =
-    raise (ref CatchableError)(msg: "hello")
+  block:
+    func raises(): int =
+      raise (ref CatchableError)(msg: "hello")
+    func raisesVoid() =
+      raise (ref CatchableError)(msg: "hello")
 
-  let c = catch:
-    raises()
-  doAssert c.isErr
+    let c = catch:
+      raises()
+    doAssert c.isErr
+
+    when (NimMajor, NimMinor) >= (1, 6):
+      # Earlier versions complain about the type of the raisesVoid expression
+      let d = catch:
+        raisesVoid()
+      doAssert d.isErr
 
   # De-reference
   when (NimMajor, NimMinor) >= (1, 6):