From 6f7f043c9b8c782f81568c330200d6ae8addee69 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Arne=20D=C3=B6ring?= <arne.doering@gmx.net>
Date: Tue, 7 May 2019 08:29:17 +0200
Subject: [PATCH] Fix type recursion check (#11144)

* fixes #3456
* add test #3456
---
 compiler/types.nim                     |  9 +++++----
 tests/types/tillegaltyperecursion3.nim | 10 ++++++++++
 2 files changed, 15 insertions(+), 4 deletions(-)
 create mode 100644 tests/types/tillegaltyperecursion3.nim

diff --git a/compiler/types.nim b/compiler/types.nim
index 199bd3352..a40a94421 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -1517,11 +1517,12 @@ proc typeMismatch*(conf: ConfigRef; info: TLineInfo, formal, actual: PType) =
     localError(conf, info, msg)
 
 proc isTupleRecursive(t: PType, cycleDetector: var IntSet): bool =
-  if t == nil: return
+  if t == nil:
+    return false
+  if cycleDetector.containsOrIncl(t.id):
+    return true
   case t.kind:
     of tyTuple:
-      if cycleDetector.containsOrIncl(t.id):
-        return true
       var cycleDetectorCopy: IntSet
       for i in  0..<t.len:
         assign(cycleDetectorCopy, cycleDetector)
@@ -1530,7 +1531,7 @@ proc isTupleRecursive(t: PType, cycleDetector: var IntSet): bool =
     of tyAlias, tyRef, tyPtr, tyGenericInst, tyVar, tyLent, tySink, tyArray, tyUncheckedArray, tySequence:
       return isTupleRecursive(t.lastSon, cycleDetector)
     else:
-      discard
+      return false
 
 proc isTupleRecursive*(t: PType): bool =
   var cycleDetector = initIntSet()
diff --git a/tests/types/tillegaltyperecursion3.nim b/tests/types/tillegaltyperecursion3.nim
new file mode 100644
index 000000000..8e1138329
--- /dev/null
+++ b/tests/types/tillegaltyperecursion3.nim
@@ -0,0 +1,10 @@
+discard """
+errormsg: "illegal recursion in type 'Weird'"
+"""
+
+# issue #3456
+
+import tables
+type
+  Weird = ref seq[Weird]
+var t = newTable[int, Weird]()