Implement the dyn() identity function

PiperOrigin-RevId: 346846292

Author: TristonianJones

conformance/BUILD

@@ -89,8 +89,6 @@ cc_binary(
             "--skip_test=timestamps/duration_conversions/toType_duration,toString_duration",
             # TODO(issues/78): Missing bytes() conversion functions
             "--skip_test=conversions/bytes",
-            # TODO(issues/80): Missing dyn() conversion functions
-            "--skip_test=conversions/dyn/dyn_heterogeneous_list",
             # TODO(issues/81): Conversion functions for int(), uint() which can be
             # uncommented when the spec changes to truncation rather than rounding.
             "--skip_test=conversions/int/double_nearest,double_nearest_neg,double_half_away_neg,double_half_away_pos",

eval/public/builtin_func_registrar.cc

@@ -1237,6 +1237,12 @@ absl::Status RegisterConversionFunctions(CelFunctionRegistry* registry,
       builtin::kDuration, false, CreateDurationFromString, registry);
   if (!status.ok()) return status;
 
+  // dyn() identity function.
+  // TODO(issues/102): strip dyn() function references at type-check time.
+  status = FunctionAdapter<CelValue, CelValue>::CreateAndRegister(
+      builtin::kDyn, false,
+      [](Arena*, CelValue value) -> CelValue { return value; }, registry);
+
   status = RegisterIntConversionFunctions(registry, options);
   if (!status.ok()) return status;
 

eval/public/builtin_func_test.cc

@@ -718,6 +718,12 @@ TEST_F(BuiltinsTest, TestDoubleConversionError_stringInvalid) {
   TestTypeConversionError(builtin::kDouble, CelValue::CreateString(&invalid));
 }
 
+TEST_F(BuiltinsTest, TestDynConversions) {
+  TestTypeConverts(builtin::kDyn, CelValue::CreateDouble(100.1), 100.1);
+  TestTypeConverts(builtin::kDyn, CelValue::CreateInt64(100L), 100L);
+  TestTypeConverts(builtin::kDyn, CelValue::CreateUint64(100UL), 100UL);
+}
+
 TEST_F(BuiltinsTest, TestIntConversions_int) {
   TestTypeConverts(builtin::kInt, CelValue::CreateInt64(100L), 100L);
 }

eval/public/cel_builtins.h

@@ -72,6 +72,7 @@ constexpr char kMilliseconds[] = "getMilliseconds";
 // Type conversions
 // TODO(issues/23): Add other type conversion methods.
 constexpr char kDouble[] = "double";
+constexpr char kDyn[] = "dyn";
 constexpr char kInt[] = "int";
 constexpr char kString[] = "string";
 constexpr char kType[] = "type";