Support using imported C++ generic types in proc signatures

compiler/ccgtypes.nim

@@ -841,6 +841,13 @@ proc getTypeDescAux(m: BModule, origTyp: PType, check: var IntSet): Rope =
       # always call for sideeffects:
       assert t.kind != tyTuple
       discard getRecordDesc(m, t, result, check)
+      # The resulting type will include commas and these won't play well
+      # with the C macros for defining procs such as N_NIMCALL. We must
+      # create a typedef for the type and use it in the proc signature:
+      let typedefName = ~"TY" & $sig
+      addf(m.s[cfsTypes], "typedef $1 $2;$n", [result, typedefName])
+      m.typeCache[sig] = typedefName
+      result = typedefName
     else:
       when false:
         if t.sym != nil and t.sym.name.s == "KeyValuePair":

tests/cpp/tcovariancerules.nim

@@ -300,7 +300,7 @@ reject wantsVarPointer2(pcat)
 
 # covariance may be allowed for certain extern types
 
-{.emit: """
+{.emit: """/*TYPESECTION*/
 template <class T> struct FN { typedef void (*type)(T); };
 template <class T> struct ARR { typedef T DataType[2]; DataType data; };
 """.}

tests/cpp/tvector_iterator.nim

@@ -2,7 +2,7 @@ discard """
   targets: "cpp"
 """
 
-{.emit: """
+{.emit: """/*TYPESECTION*/
 
 template <class T>
 struct Vector {

tests/statictypes/tstaticimportcpp.nim

@@ -1,9 +1,9 @@
 discard """
 targets: "cpp"
-output: "[0, 0, 10, 0]\n5\n1.2\n15\ntest"
+output: "[0, 0, 10, 0]\n5\n1.2\n15\ntest\n[0, 0, 20, 0]"
 """
 
-{.emit: """
+{.emit: """/*TYPESECTION*/
 
 template <int N, class T>
 struct GenericIntType {
@@ -51,3 +51,9 @@ echo c.field
 echo d.field
 echo e.field
 
+proc plus(a, b: GenInt4): GenInt4 =
+  for i in 0 ..< result.data.len:
+    result.data[i] = a.data[i] + b.data[i]
+
+echo plus(a, a).data
+