Reject enums with holes when computedGoto is used (#8132)

Fixes #7699

compiler/ccgstmts.nim

@@ -404,6 +404,9 @@ proc genComputedGoto(p: BProc; n: PNode) =
         localError(p.config, it.info,
             "case statement must be exhaustive for computed goto"); return
       casePos = i
+      if enumHasHoles(it.sons[0].typ):
+        localError(p.config, it.info,
+            "case statement cannot work on enums with holes for computed goto"); return
       let aSize = lengthOrd(p.config, it.sons[0].typ)
       if aSize > 10_000:
         localError(p.config, it.info,

tests/casestmt/t7699.nim

@@ -0,0 +1,15 @@
+discard """
+  line: 13
+  errormsg: "case statement cannot work on enums with holes for computed goto"
+"""
+
+type
+  X = enum
+    A = 0, B = 100
+
+var z = A
+while true:
+  {.computedGoto.}
+  case z
+  of A: discard
+  of B: discard