Dotborrow now works with generic distincts (#18848)

tests/borrow/tborrow.nim

@@ -33,3 +33,23 @@ let b = Radians(1.0)
 a -= b
 
 echo a.float64
+
+block: #14449
+  type 
+    Foo[T] = object
+      foo: T
+
+    Bar[T] {.borrow:`.`.} = distinct Foo[T]
+    SomeThing {.borrow:`.`.} = distinct Foo[float]
+    OtherThing {.borrow:`.`.} = distinct SomeThing
+
+  var
+    a: Bar[int]
+    b: SomeThing
+    c: OtherThing
+  a.foo = 300
+  b.foo = 400
+  c.foo = 42
+  assert a.foo == 300
+  assert b.foo == 400d
+  assert c.foo == 42d

tests/borrow/tinvalidborrow.nim

@@ -1,16 +1,25 @@
 discard """
-  errormsg: "no symbol to borrow from found"
-  line: 11
+  cmd: "nim check --hints:off --warnings:off $file"
+  action: "reject"
+  nimout:'''
+tinvalidborrow.nim(18, 3) Error: only a 'distinct' type can borrow `.`
+tinvalidborrow.nim(19, 3) Error: only a 'distinct' type can borrow `.`
+tinvalidborrow.nim(20, 1) Error: no symbol to borrow from found
+'''
 """
 
 # bug #516
 
 type
   TAtom = culong
-
+  Test {.borrow:`.`.} = distinct int
+  Foo[T] = object
+    a: int
+  Bar[T] {.borrow:`.`.} = Foo[T]
+  OtherFoo {.borrow:`.`.} = Foo[int]
 proc `==`*(a, b: TAtom): bool {.borrow.}
 
 var
   d, e: TAtom
 
-echo( $(d == e) )
+discard( $(d == e) )