fixes #3055

compiler/seminst.nim

@@ -205,7 +205,7 @@ proc instantiateProcType(c: PContext, pt: TIdTable,
   # The solution would be to move this logic into semtypinst, but
   # at this point semtypinst have to become part of sem, because it
   # will need to use openScope, addDecl, etc.
-  addDecl(c, prc)
+  #addDecl(c, prc)
 
   pushInfoContext(info)
   var cl = initTypeVars(c, pt, info, nil)

tests/generics/tforward_generic.nim

@@ -0,0 +1,28 @@
+discard """
+  output: '''b()
+720 120.0'''
+"""
+
+# bug #3055
+proc b(t: int | string)
+proc a(t: int) = b(t)
+proc b(t: int | string) = echo "b()"
+a(1)
+
+# test recursive generics still work:
+proc fac[T](x: T): T =
+  if x == 0: return 1
+  else: return fac(x-1)*x
+
+echo fac(6), " ", fac(5.0)
+
+when false:
+  # This still doesn't work...
+  # test recursive generic with forwarding:
+  proc fac2[T](x: T): T
+
+  echo fac2(6), " ", fac2(5.0)
+
+  proc fac2[T](x: T): T =
+    if x == 0: return 1
+    else: return fac2(x-1)*x