Creating and setting comment nodes in macros (#5850)

* strVal assingnable comment statement ast nodes
* Set comment instead of strVal for comment nodes
* Added test code for creating and setting comment nodes
* Modified the AST spec documentation for documentation comments

compiler/vm.nim

@@ -1406,6 +1406,8 @@ proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
       if dest.kind in {nkStrLit..nkTripleStrLit} and
          regs[rb].kind in {rkNode}:
         dest.strVal = regs[rb].node.strVal
+      elif dest.kind == nkCommentStmt:
+        dest.comment = regs[rb].node.strVal
       else:
         stackTrace(c, tos, pc, errFieldXNotFound, "strVal")
     of opcNNewNimNode:

doc/astspec.txt

@@ -461,8 +461,8 @@ Documentation Comments
 ----------------------
 
 Double-hash (``##``) comments in the code actually have their own format,
-but the comments do not yet show up in the AST, which will only show that
-a comment exists, not what it contains. Single-hash (``#``) comments are ignored.
+using ``strVal`` to get and set the comment text. Single-hash (``#``) 
+comments are ignored.
 
 Concrete syntax:
 

tests/vm/tnimnode.nim

@@ -72,3 +72,11 @@ static:
   echo "OK"
   
 
+static:
+  echo "testing creation of comment node"
+  var docComment: NimNode = newNimNode(nnkCommentStmt)
+  docComment.strVal = "This is a doc comment"
+
+  assertEq repr(docComment), "## This is a doc comment"
+
+  echo "OK"