closes #4678; add testcase (#20634)

tests/cpp/torc.nim

@@ -23,3 +23,19 @@ type
 
 var b = Bar()
 discard b
+
+# bug #4678
+{.emit: """/*TYPESECTION*/
+enum class SomeEnum {A,B,C};
+""".}
+type
+  EnumVector[T: enum] {.importcpp: "std::vector", header: "vector".} = object
+  SomeEnum {.importcpp, nodecl.} = enum
+    A,B,C
+
+proc asVector*[T](t: T): EnumVector[T] =
+  discard
+# Nim generates this signature here:
+# N_NIMCALL(std::vector<> , asvector_106028_3197418230)(SomeEnum t0)
+
+discard asVector(SomeEnum.A)