macros are now checked to not produce cyclic ASTs

compiler/evaltempl.nim

@@ -121,7 +121,6 @@ proc wrapInComesFrom*(info: TLineInfo; res: PNode): PNode =
   else:
     result = newNodeI(nkPar, info)
     result.add res
-    result.flags.incl nfNone
 
 proc evalTemplate*(n: PNode, tmpl, genSymOwner: PSym; fromHlo=false): PNode =
   inc(evalTemplateCounter)

compiler/sem.nim

@@ -237,6 +237,14 @@ when false:
     result.handleIsOperator = proc (n: PNode): PNode =
       result = isOpImpl(c, n)
 
+proc hasCycle(n: PNode): bool =
+  incl n.flags, nfNone
+  for i in 0..<safeLen(n):
+    if nfNone in n[i].flags or hasCycle(n[i]):
+      result = true
+      break
+  excl n.flags, nfNone
+
 proc fixupTypeAfterEval(c: PContext, evaluated, eOrig: PNode): PNode =
   # recompute the types as 'eval' isn't guaranteed to construct types nor
   # that the types are sound:
@@ -246,6 +254,10 @@ proc fixupTypeAfterEval(c: PContext, evaluated, eOrig: PNode): PNode =
     else:
       result = evaluated
       let expectedType = eOrig.typ.skipTypes({tyStatic})
+      if hasCycle(result):
+        globalError(eOrig.info, "the resulting AST is cyclic and cannot be processed further")
+        result = errorNode(c, eOrig)
+      else:
         semmacrosanity.annotateType(result, expectedType)
   else:
     result = semExprWithType(c, evaluated)