fix complex typdesc iterators

compiler/transf.nim

@@ -560,6 +560,7 @@ type
 proc putArgInto(arg: PNode, formal: PType): TPutArgInto =
   # This analyses how to treat the mapping "formal <-> arg" in an
   # inline context.
+  if formal.kind == tyTypeDesc: return paDirectMapping
   if skipTypes(formal, abstractInst).kind in {tyOpenArray, tyVarargs}:
     if arg.kind == nkStmtListExpr:
       return paComplexOpenarray

tests/iter/titertypedesc.nim

@@ -0,0 +1,17 @@
+discard """
+  output: '''0
+(id: 0)
+@[]
+[0, 0, 0]'''
+"""
+
+iterator foo*(T: typedesc): T =
+  var x: T
+  yield x
+
+for a in foo(int): echo a
+for b in foo(tuple[id: int]): echo b
+for c in foo(seq[int]): echo c
+
+type Generic[T] = T
+for d in foo(Generic[array[0..2, int]]): echo d