Update assignability check to allow wrapper types to match their corresponding primitives.

PiperOrigin-RevId: 689153309

Author: jnthntatum

checker/internal/type_checker_impl_test.cc

@@ -1306,11 +1306,14 @@ struct CheckedExprTestCase {
 class WktCreationTest : public testing::TestWithParam<CheckedExprTestCase> {};
 
 TEST_P(WktCreationTest, MessageCreation) {
+  google::protobuf::Arena arena;
   const CheckedExprTestCase& test_case = GetParam();
   TypeCheckEnv env;
   env.AddTypeProvider(std::make_unique<TypeIntrospector>());
   env.set_container("google.protobuf");
 
+  ASSERT_THAT(RegisterMinimalBuiltins(&arena, env), IsOk());
+
   TypeCheckerImpl impl(std::move(env));
   ASSERT_OK_AND_ASSIGN(auto ast, MakeTestParsedAst(test_case.expr));
   ASSERT_OK_AND_ASSIGN(ValidationResult result, impl.Check(std::move(ast)));
@@ -1450,6 +1453,15 @@ INSTANTIATE_TEST_SUITE_P(
                 value: b''
               })cel",
             .expected_result_type = AstType(ast_internal::WellKnownType::kAny),
+        },
+        CheckedExprTestCase{
+            .expr = "Int64Value{value: 10} + 1",
+            .expected_result_type =
+                AstType(ast_internal::PrimitiveType::kInt64),
+        },
+        CheckedExprTestCase{
+            .expr = "BoolValue{value: false} || true",
+            .expected_result_type = AstType(ast_internal::PrimitiveType::kBool),
         }));
 
 class GenericMessagesTest : public testing::TestWithParam<CheckedExprTestCase> {

checker/internal/type_inference_context.cc

@@ -287,6 +287,15 @@ bool TypeInferenceContext::IsAssignableInternal(
     return true;
   }
 
+  // Wrapper types are assignable to their corresponding primitive type (
+  // somewhat similar to auto unboxing). This is a bit odd with CEL's null_type,
+  // but there isn't a dedicated syntax for narrowing from the nullable.
+  if (auto from_wrapper = WrapperToPrimitive(from_subs);
+      from_wrapper.has_value()) {
+    return IsAssignableInternal(*from_wrapper, to_subs,
+                                prospective_substitutions);
+  }
+
   if (enable_legacy_null_assignment_) {
     if (from_subs.IsNull() && IsLegacyNullable(to_subs)) {
       return true;