fixes #23869; sink generic typeclass (#23874)

Still have to look this over some. We'll see. I put sink in this branch
simply because I saw `tyVar` there and for no other reason. In any case
the problem appears to be coming from `liftParamType` as it removes the
`sink` type from the formals.
#23869

1 files changed, 26 insertions, 0 deletions

diff --git a/tests/proc/t23874.nim b/tests/proc/t23874.nim
new file mode 100644
index 000000000..940bc4ac8
--- /dev/null
+++ b/tests/proc/t23874.nim
@@ -0,0 +1,26 @@
+block:
+  type Head[T] = object
+    wasc: bool
+
+  proc `=destroy`[T](x: var Head[T]) =
+    discard
+
+  proc `=copy`[T](x: var Head[T], y: Head[T]) =
+    x.wasc = true
+
+  proc `=dup`[T](x: Head[T]): Head[T] =
+    result.wasc = true
+
+  proc update(h: var Head) =
+    discard
+
+  proc digest(h: sink Head) =
+    assert h.wasc
+
+  var h = Head[int](wasc: false)
+  h.digest() # sink h
+  h.update() # use after sink
+
+block:
+  proc two(a: sink auto) =discard
+  assert typeof(two[int]) is proc(a: sink int) {.nimcall.}