From f915b3aa86929d87e162b6ddd7589e6337a30397 Mon Sep 17 00:00:00 2001
From: Jason Beetham <beefers331@gmail.com>
Date: Thu, 30 Sep 2021 08:55:43 -0600
Subject: [PATCH] Alternative to #18928 (#18931)

* fixed #18841

* Added test
---
 compiler/semtypinst.nim               | 12 +++----
 tests/generics/trecursivegenerics.nim | 52 ++++++++++++++++++++++++++-
 2 files changed, 57 insertions(+), 7 deletions(-)

diff --git a/compiler/semtypinst.nim b/compiler/semtypinst.nim
index 2ca355e7d0..0bb53e04df 100644
--- a/compiler/semtypinst.nim
+++ b/compiler/semtypinst.nim
@@ -344,11 +344,7 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
       x = lookupTypeVar(cl, x)
       if x != nil:
         if header == t: header = instCopyType(cl, t)
-        header[i] =
-          if x.kind == tyGenericInst:
-            t[i]
-          else:
-            x
+        header[i] = x
         propagateToOwner(header, x)
     else:
       propagateToOwner(header, x)
@@ -382,7 +378,11 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
   cl.typeMap = newTypeMapLayer(cl)
 
   for i in 1..<t.len:
-    var x = replaceTypeVarsT(cl, header[i])
+    var x = replaceTypeVarsT(cl):
+      if header[i].kind == tyGenericInst:
+        t[i]
+      else:
+        header[i]
     assert x.kind != tyGenericInvocation
     header[i] = x
     propagateToOwner(header, x)
diff --git a/tests/generics/trecursivegenerics.nim b/tests/generics/trecursivegenerics.nim
index e4c0e720f0..1b152b0635 100644
--- a/tests/generics/trecursivegenerics.nim
+++ b/tests/generics/trecursivegenerics.nim
@@ -43,4 +43,54 @@ block:
     ItemSimple = ref object
       link:DoublyLinkedNode[ ItemSimple ]
 
-  let link = newDoublyLinkedNode( Item[Box]() )
\ No newline at end of file
+  let link = newDoublyLinkedNode( Item[Box]() )
+
+block: #18897
+  type
+    SkipListObj[T] = object
+      over: SkipList[T]
+      down: SkipList[T]
+      value: T
+
+    SkipList[T] = ref SkipListObj[T]
+
+    GraphObj[N, E; F: static[int]] = object
+      nodes: SkipList[Node[N, E]]
+
+    Graph[N, E; F: static[int]] = ref GraphObj[N, E, F]
+
+    Node[N, E] = ref NodeObj[N, E]
+
+    NodeObj[N, E] = object
+      value: N
+      incoming: SkipList[Edge[N, E]]
+      outgoing: SkipList[Edge[N, E]]
+
+    Edge[N, E] = ref EdgeObj[N, E]
+
+    EdgeObj[N, E] = object
+      value: E
+      id: int
+      source: Node[N, E]
+      target: Node[N, E]
+
+    EdgeResult[N, E] = tuple
+      source: Node[N, E]
+      edge: Edge[N, E]
+      target: Node[N, E]
+
+  proc newSkipList[T](value: T): SkipList[T] =
+    static: echo T, " ", typeof(result.value)
+    result = SkipList[T](value: value)
+
+  proc toSkipList[T](values: openArray[T] = @[]): SkipList[T] =
+    for item in items(values):
+      if result.isNil:
+        result = newSkipList(item)
+
+  proc newContainer[N, E, F](graph: Graph[N, E, F]; form: typedesc): auto =
+    result = toSkipList[form]([])
+
+  var
+    result = Graph[int, string, 0]()
+  result.nodes = result.newContainer(Node[int, string])
\ No newline at end of file