fixes #6016 union alias trigger bad codegen (#6117)

* fixes #6016 union alias trigger bad codegen
* cpp test ok
* merging some test into one file

tests/types/taliasbugs.nim

@@ -0,0 +1,158 @@
+discard """
+  msg: '''true
+true
+true
+true
+true
+true'''
+  output: '''true
+true
+true
+true
+true
+true
+R
+R
+R
+R
+19
+(c: 0)
+(c: 13)
+@[(c: 11)]
+@[(c: 17)]
+100'''
+"""
+
+# bug #5360
+import macros
+
+type
+  Order = enum
+    R
+  OrderAlias = Order
+
+template getOrderTypeA(): typedesc = Order
+template getOrderTypeB(): typedesc = OrderAlias
+
+type
+  OrderR    = getOrderTypeA()
+  OrderG    = getOrderTypeB()
+
+macro typeRep(a, b: typed): untyped =
+  if sameType(a, b):
+    echo "true"
+  else:
+    echo "false"
+
+template test(a, b: typedesc) =
+  when a is b:
+    echo "true"
+  else:
+    echo "false"
+
+test(OrderAlias, Order)
+test(OrderR, Order)
+test(OrderG, Order)
+
+test(OrderR, OrderG)
+test(OrderR, OrderAlias)
+test(OrderG, OrderAlias)
+
+typeRep(OrderAlias.R, Order.R)  # true
+typeRep(OrderR.R, Order.R)      # true
+typeRep(OrderG.R, Order.R)      # true
+
+typeRep(OrderR.R, OrderAlias.R) # true
+typeRep(OrderG.R, OrderAlias.R) # true
+typeRep(OrderR.R, OrderG.R)     # true
+
+echo OrderR.R      # R
+echo OrderG.R      # R
+echo OrderAlias.R  # R
+echo Order.R       # R
+
+# bug #5238
+
+type
+  Rgba8 = object
+    c: int
+  BlenderRgb*[ColorT] = object
+
+template getColorType*[C](x: typedesc[BlenderRgb[C]]): typedesc = C
+
+type
+  ColorT = getColorType(BlenderRgb[int])
+
+proc setColor(c: var ColorT) =
+  c = 19
+
+var n: ColorT
+n.setColor()
+echo n
+
+type
+  ColorType = getColorType(BlenderRgb[Rgba8])
+
+var x: ColorType
+echo x
+
+proc setColor(c: var ColorType) =
+  c = Rgba8(c: 13)
+
+proc setColor(c: var seq[ColorType]) =
+  c[0] = Rgba8(c: 11)
+
+proc setColorArray(c: var openArray[ColorType]) =
+  c[0] = Rgba8(c: 17)
+
+x.setColor()
+echo x
+
+var y = @[Rgba8(c:15)]
+y.setColor()
+echo y
+
+y.setColorArray()
+echo y
+
+#bug #6016
+type
+  Onion {.union.} = object
+    field1: int
+    field2: uint64
+
+  Stroom  = Onion
+
+  PStroom = ptr Stroom
+
+proc pstruct(u: PStroom) =
+  echo u.field2
+
+var oni = Onion(field1: 100)
+pstruct(oni.addr)
+
+
+# bug #4124
+
+import sequtils
+
+type
+    Foo = distinct string
+
+var
+  foo: Foo
+
+type
+    Alias = (type(foo))
+var
+  a: Alias
+
+a = foo
+
+when true:
+  var xs = @[1,2,3]
+
+  proc asFoo(i: string): Foo =
+      Foo(i)
+
+  var xx = xs.mapIt(asFoo($(it + 5)))