From 4ec39b6a8ff4b0f1cfd60f605f60284f0226290e Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Wed, 8 Feb 2017 11:33:36 +0100
Subject: [PATCH] macros are now checked to not produce cyclic ASTs

---
 compiler/evaltempl.nim |  1 -
 compiler/sem.nim       | 14 +++++++++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/compiler/evaltempl.nim b/compiler/evaltempl.nim
index 87745f7edf..318254a809 100644
--- a/compiler/evaltempl.nim
+++ b/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)
diff --git a/compiler/sem.nim b/compiler/sem.nim
index d3349a7507..dbf2376357 100644
--- a/compiler/sem.nim
+++ b/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:
@@ -246,7 +254,11 @@ proc fixupTypeAfterEval(c: PContext, evaluated, eOrig: PNode): PNode =
     else:
       result = evaluated
       let expectedType = eOrig.typ.skipTypes({tyStatic})
-      semmacrosanity.annotateType(result, expectedType)
+      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)
     #result = fitNode(c, e.typ, result) inlined with special case: