refactor: introduce syntax/expression package (kyverno#491)

Signed-off-by: Charles-Edouard Brétéché <[email protected]>

pkg/engine/assert/binding.go

@@ -6,27 +6,37 @@ import (
 	"github.com/jmespath-community/go-jmespath/pkg/binding"
 	"github.com/kyverno/kyverno-json/pkg/engine/template"
 	"github.com/kyverno/kyverno-json/pkg/jp"
+	"github.com/kyverno/kyverno-json/pkg/syntax/expression"
 	"k8s.io/apimachinery/pkg/util/validation/field"
 )
 
 func NewContextBinding(path *field.Path, bindings binding.Bindings, value any, entry any, opts ...template.Option) binding.Binding {
 	return jp.NewLazyBinding(
 		func() (any, error) {
-			expression := parseExpression(context.TODO(), entry)
-			if expression != nil && expression.engine != "" {
-				if expression.foreach {
-					return nil, field.Invalid(path.Child("variable"), entry, "foreach is not supported in context")
+			switch typed := entry.(type) {
+			case string:
+				expr := expression.Parse(typed)
+				if expr.Foreach {
+					return nil, field.Invalid(path.Child("variable"), typed, "foreach is not supported in context")
 				}
-				if expression.binding != "" {
-					return nil, field.Invalid(path.Child("variable"), entry, "binding is not supported in context")
+				if expr.Binding != "" {
+					return nil, field.Invalid(path.Child("variable"), typed, "binding is not supported in context")
 				}
-				projected, err := template.Execute(context.TODO(), expression.statement, value, bindings, opts...)
-				if err != nil {
-					return nil, field.InternalError(path.Child("variable"), err)
+				switch expr.Engine {
+				case expression.EngineJP:
+					projected, err := template.Execute(context.TODO(), expr.Statement, value, bindings, opts...)
+					if err != nil {
+						return nil, field.InternalError(path.Child("variable"), err)
+					}
+					return projected, nil
+				case expression.EngineCEL:
+					return nil, field.Invalid(path.Child("variable"), expr.Engine, "engine not supported")
+				default:
+					return expr.Statement, nil
 				}
-				return projected, nil
+			default:
+				return typed, nil
 			}
-			return entry, nil
 		},
 	)
 }