make var object match better than object (#22152)

* fix `var object` not matching better than `object`

fixes #13302

* remove comment for brevity

* try note

* try minimize breaks

(cherry picked from commit 20037a4749)

compiler/sigmatch.nim

@@ -211,7 +211,7 @@ proc sumGeneric(t: PType): int =
   # and Foo[T] has the value 2 so that we know Foo[Foo[T]] is more
   # specific than Foo[T].
   var t = t
-  var isvar = 1
+  var isvar = 0
   while true:
     case t.kind
     of tyGenericInst, tyArray, tyRef, tyPtr, tyDistinct, tyUncheckedArray,
@@ -247,6 +247,8 @@ proc sumGeneric(t: PType): int =
     of tyBool, tyChar, tyEnum, tyObject, tyPointer,
         tyString, tyCstring, tyInt..tyInt64, tyFloat..tyFloat128,
         tyUInt..tyUInt64, tyCompositeTypeClass:
+      return isvar + 1
+    of tyBuiltInTypeClass:
       return isvar
     else:
       return 0

tests/overload/tvartypeclass.nim

@@ -0,0 +1,11 @@
+# issue #13302
+
+proc foo(x: object): int = x.i*2
+proc foo(x: var object) = x.i*=2
+type Foo = object
+  i: int
+let x = Foo(i: 3)
+var y = Foo(i: 4)
+doAssert foo(x) == 6
+foo(y)
+doAssert y.i == 8