From 6cb8bf8045b72180d66c4e6c26f47435406a0252 Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Mon, 30 Oct 2017 09:18:47 +0100
Subject: [PATCH] fixes bug reported in PR #5637

---
 compiler/ast.nim                       | 8 ++++++++
 compiler/semtypes.nim                  | 5 ++++-
 tests/types/tillegaltyperecursion2.nim | 8 ++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 tests/types/tillegaltyperecursion2.nim

diff --git a/compiler/ast.nim b/compiler/ast.nim
index e6d967dde1..176c2edca2 100644
--- a/compiler/ast.nim
+++ b/compiler/ast.nim
@@ -1387,6 +1387,14 @@ proc skipTypes*(t: PType, kinds: TTypeKinds): PType =
   result = t
   while result.kind in kinds: result = lastSon(result)
 
+proc skipTypes*(t: PType, kinds: TTypeKinds; maxIters: int): PType =
+  result = t
+  var i = maxIters
+  while result.kind in kinds:
+    result = lastSon(result)
+    dec i
+    if i == 0: return nil
+
 proc skipTypesOrNil*(t: PType, kinds: TTypeKinds): PType =
   ## same as skipTypes but handles 'nil'
   result = t
diff --git a/compiler/semtypes.nim b/compiler/semtypes.nim
index 18ea873411..8c4ad81ad4 100644
--- a/compiler/semtypes.nim
+++ b/compiler/semtypes.nim
@@ -1167,7 +1167,10 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
 
   # special check for generic object with
   # generic/partial specialized parent
-  let tx = result.skipTypes(abstractPtrs)
+  let tx = result.skipTypes(abstractPtrs, 50)
+  if tx.isNil:
+    localError(n.info, "invalid recursion in type '$1'" % typeToString(result[0]))
+    return errorType(c)
   if tx != result and tx.kind == tyObject and tx.sons[0] != nil:
     semObjectTypeForInheritedGenericInst(c, n, tx)
 
diff --git a/tests/types/tillegaltyperecursion2.nim b/tests/types/tillegaltyperecursion2.nim
new file mode 100644
index 0000000000..b5ffdda72b
--- /dev/null
+++ b/tests/types/tillegaltyperecursion2.nim
@@ -0,0 +1,8 @@
+discard """
+  errormsg: "invalid recursion in type 'Executor'"
+  line: 8
+"""
+# bug reported by PR #5637
+type
+  Executor[N] = Executor[N]
+var e: Executor[int]