close #8558(add testcase for #8558) (#15872)

tests/concepts/t8558.nim

@@ -0,0 +1,26 @@
+discard """
+  output: '''10
+9
+8
+7
+6
+5
+4
+3
+2
+1
+go!
+'''
+"""
+
+type Integral = concept x
+  x == 0 is bool
+  x - 1 is type(x)
+
+proc countToZero(n: Integral) =
+  if n == 0: echo "go!"
+  else:
+    echo n
+    countToZero(n-1)
+
+countToZero(10)