Add strings extension

Signed-off-by: Alex Snaps <[email protected]>

pkg/expressions/cel/expressions.go

@@ -9,6 +9,7 @@ import (
 	"github.com/google/cel-go/cel"
 	"github.com/google/cel-go/checker/decls"
 	"github.com/google/cel-go/common/types/ref"
+	"github.com/google/cel-go/ext"
 	"google.golang.org/protobuf/encoding/protojson"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/structpb"
@@ -130,6 +131,7 @@ func Compile(expression string, expectedType *cel.Type, opts ...cel.EnvOption) (
 		decls.NewConst(RootDestinationBinding, decls.NewObjectType("google.protobuf.Struct"), nil),
 		decls.NewConst(RootAuthBinding, decls.NewObjectType("google.protobuf.Struct"), nil),
 	)}, opts...)
+	envOpts = append(envOpts, ext.Strings())
 	env, env_err := cel.NewEnv(envOpts...)
 	if env_err != nil {
 		return nil, env_err

pkg/expressions/cel/expressions_test.go

@@ -42,3 +42,14 @@ func TestPredicate(t *testing.T) {
 	assert.NilError(t, err)
 	assert.Equal(t, response, true)
 }
+
+func TestExpression(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+
+	expression, err := NewStringExpression(`"hello hello".replace("", "_")`)
+	assert.NilError(t, err)
+	resolveFor, err := expression.ResolveFor("{}")
+	assert.NilError(t, err)
+	assert.Equal(t, resolveFor, "_h_e_l_l_o_ _h_e_l_l_o_")
+}