Extension to support Golang structs as CEL types (#612)

 Implementation of a Golang native type provider

cel/cel_test.go

@@ -1878,7 +1878,7 @@ func TestDynamicDispatch(t *testing.T) {
 
 func TestOptionalValues(t *testing.T) {
 	env, err := NewEnv(
-		OptionalTypes(true),
+		OptionalTypes(),
 		// Container and test message types.
 		Container("google.expr.proto2.test"),
 		Types(&proto2pb.TestAllTypes{}),
@@ -2205,7 +2205,7 @@ func TestOptionalValues(t *testing.T) {
 
 func BenchmarkOptionalValues(b *testing.B) {
 	env, err := NewEnv(
-		OptionalTypes(true),
+		OptionalTypes(),
 		Variable("x", OptionalType(IntType)),
 		Variable("y", OptionalType(IntType)),
 		Variable("z", IntType),

cel/env.go

@@ -485,11 +485,6 @@ func (e *Env) configure(opts []EnvOption) (*Env, error) {
 	if err != nil {
 		return nil, err
 	}
-	// If optional types have been enabled, then configure the optional library.
-	e, err = e.maybeApplyFeature(featureOptionalTypes, Lib(optionalLibrary{}))
-	if err != nil {
-		return nil, err
-	}
 
 	// Initialize all of the functions configured within the environment.
 	for _, fn := range e.functions {

cel/library.go

@@ -157,7 +157,7 @@ func (optionalLibrary) CompileOptions() []EnvOption {
 					return opt.GetValue()
 				}))),
 		Function("hasValue",
-			MemberOverload("optional_hasValue", []*Type{optionalTypeV}, paramTypeV,
+			MemberOverload("optional_hasValue", []*Type{optionalTypeV}, BoolType,
 				UnaryBinding(func(value ref.Val) ref.Val {
 					opt := value.(*types.Optional)
 					return types.Bool(opt.HasValue())

cel/options.go

@@ -542,11 +542,11 @@ func DefaultUTCTimeZone(enabled bool) EnvOption {
 	return features(featureDefaultUTCTimeZone, enabled)
 }
 
-// OptionalTypes determines whether CEL's optional value type is enabled. The optional value type makes it
-// possible to express whether variables have been provided, whether a result has been computed, and
-// in the future whether an object field path, map key value, or list index has a value.
-func OptionalTypes(enabled bool) EnvOption {
-	return features(featureOptionalTypes, enabled)
+// OptionalTypes enable support for optional syntax and types in CEL. The optional value type makes
+// it possible to express whether variables have been provided, whether a result has been computed,
+// and in the future whether an object field path, map key value, or list index has a value.
+func OptionalTypes() EnvOption {
+	return Lib(optionalLibrary{})
 }
 
 // features sets the given feature flags.  See list of Feature constants above.

common/types/ref/provider.go

@@ -39,8 +39,6 @@ type TypeProvider interface {
 
 	// FieldFieldType returns the field type for a checked type value. Returns
 	// false if the field could not be found.
-	//
-	// Used during type-checking only.
 	FindFieldType(messageType string, fieldName string) (*FieldType, bool)
 
 	// NewValue creates a new type value from a qualified name and map of field