Fix some bounds in rapid check instances

`inRange` is exclusive not inclusive:
https://github.com/emil-e/rapidcheck/blob/master/doc/generators.md#usage

Furthermore, use `std::variant_size_v` so we use the right number
automatically.

Finally, make the `switch` assert the discriminant is in bounds as
expected.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libexpr/tests/value/context.cc b/src/libexpr/tests/value/context.cc
index 27d6920b0..0d9381577 100644
--- a/src/libexpr/tests/value/context.cc
+++ b/src/libexpr/tests/value/context.cc
@@ -95,13 +95,15 @@ Gen<NixStringContextElem::Built> Arbitrary<NixStringContextElem::Built>::arbitra
 
 Gen<NixStringContextElem> Arbitrary<NixStringContextElem>::arbitrary()
 {
-    switch (*gen::inRange<uint8_t>(0, 2)) {
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<NixStringContextElem::Raw>)) {
     case 0:
         return gen::just<NixStringContextElem>(*gen::arbitrary<NixStringContextElem::Opaque>());
     case 1:
         return gen::just<NixStringContextElem>(*gen::arbitrary<NixStringContextElem::DrvDeep>());
-    default:
+    case 2:
         return gen::just<NixStringContextElem>(*gen::arbitrary<NixStringContextElem::Built>());
+    default:
+        assert(false);
     }
 }