[torque] allow conditionals with enum constants

Bug: v8:7793, v8:10475
Change-Id: I3c528d07e8d3192d7110ebc81e9e89f79a7c735d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2196132Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67764}

src/torque/types.h

@@ -275,6 +275,7 @@ class AbstractType final : public Type {
   const Type* NonConstexprVersion() const override {
     if (non_constexpr_version_) return non_constexpr_version_;
     if (!IsConstexpr()) return this;
+    if (parent()) return parent()->NonConstexprVersion();
     return nullptr;
   }
 
@@ -431,6 +432,13 @@ class V8_EXPORT_PRIVATE UnionType final : public Type {
     return false;
   }
 
+  bool IsConstexpr() const override { return parent()->IsConstexpr(); }
+
+  const Type* NonConstexprVersion() const override {
+    if (!IsConstexpr()) return this;
+    return parent()->NonConstexprVersion();
+  }
+
   void Extend(const Type* t) {
     if (const UnionType* union_type = UnionType::DynamicCast(t)) {
       for (const Type* member : union_type->types_) {

test/unittests/torque/torque-unittest.cc

@@ -643,6 +643,20 @@ TEST(Torque, EnumInTypeswitch) {
       }
     }
   )");
+
+  ExpectSuccessfulCompilation(R"(
+  extern enum MyEnum extends Smi {
+    kA,
+    kB,
+    kC,
+    ...
+  }
+
+  @export
+  macro Test(implicit context: Context)(b: bool): Smi {
+    return b ? MyEnum::kB : MyEnum::kA;
+  }
+)");
 }
 
 TEST(Torque, ConstClassFields) {