feat: support print statement in gator (#2949)

cmd/gator/verify/verify.go

@@ -112,7 +112,7 @@ func runE(cmd *cobra.Command, args []string) error {
 func runSuites(ctx context.Context, fileSystem fs.FS, suites []*verify.Suite, filter verify.Filter) error {
 	isFailure := false
 
-	runner, err := verify.NewRunner(fileSystem, gator.NewOPAClient, verify.IncludeTrace(includeTrace), verify.UseK8sCEL(flagEnableK8sCel))
+	runner, err := verify.NewRunner(fileSystem, gator.NewOPAClient, verify.IncludeTrace(includeTrace), verify.EnablePrint(verbose), verify.UseK8sCEL(flagEnableK8sCel))
 	if err != nil {
 		return err
 	}

pkg/gator/opa.go

@@ -6,9 +6,10 @@ import (
 	"github.com/open-policy-agent/gatekeeper/v3/pkg/drivers/k8scel"
 	"github.com/open-policy-agent/gatekeeper/v3/pkg/target"
 	"github.com/open-policy-agent/gatekeeper/v3/pkg/util"
+	"os"
 )
 
-func NewOPAClient(includeTrace bool, k8sCEL bool) (Client, error) {
+func NewOPAClient(includeTrace bool, printEnabled bool, k8sCEL bool) (Client, error) {
 	args := []constraintclient.Opt{constraintclient.Targets(&target.K8sValidationTarget{})}
 
 	if k8sCEL {
@@ -19,7 +20,18 @@ func NewOPAClient(includeTrace bool, k8sCEL bool) (Client, error) {
 		args = append(args, constraintclient.Driver(k8sDriver))
 	}
 
-	driver, err := rego.New(rego.Tracing(includeTrace))
+	driverArgs := []rego.Arg{
+		rego.Tracing(includeTrace),
+	}
+
+	if printEnabled {
+		driverArgs = append(driverArgs,
+			rego.PrintEnabled(printEnabled),
+			rego.PrintHook(NewPrintHook(os.Stdout)),
+		)
+	}
+
+	driver, err := rego.New(driverArgs...)
 	if err != nil {
 		return nil, err
 	}

pkg/gator/print.go

@@ -0,0 +1,20 @@
+package gator
+
+import (
+	"fmt"
+	v1 "github.com/open-policy-agent/opa/v1/topdown/print"
+	"io"
+)
+
+type PrintHook struct {
+	writer io.Writer
+}
+
+func NewPrintHook(writer io.Writer) PrintHook {
+	return PrintHook{writer}
+}
+
+func (h PrintHook) Print(ctx v1.Context, string string) error {
+	_, err := fmt.Fprintln(h.writer, string)
+	return err
+}

pkg/gator/verify/runner.go

@@ -34,16 +34,18 @@ type Runner struct {
 
 	// newClient instantiates a Client for compiling Templates/Constraints, and
 	// validating objects against them.
-	newClient func(includeTrace bool, useK8sCEL bool) (gator.Client, error)
+	newClient func(includeTrace bool, printEnabled bool, useK8sCEL bool) (gator.Client, error)
 
 	scheme *runtime.Scheme
 
 	includeTrace bool
 
+	printEnabled bool
+
 	useK8sCEL bool
 }
 
-func NewRunner(filesystem fs.FS, newClient func(includeTrace bool, useK8sCEL bool) (gator.Client, error), opts ...RunnerOptions) (*Runner, error) {
+func NewRunner(filesystem fs.FS, newClient func(includeTrace bool, printEnabled bool, useK8sCEL bool) (gator.Client, error), opts ...RunnerOptions) (*Runner, error) {
 	s := runtime.NewScheme()
 	err := apis.AddToScheme(s)
 	if err != nil {
@@ -71,6 +73,12 @@ func IncludeTrace(includeTrace bool) RunnerOptions {
 	}
 }
 
+func EnablePrint(printEnabled bool) RunnerOptions {
+	return func(r *Runner) {
+		r.printEnabled = printEnabled
+	}
+}
+
 func UseK8sCEL(useK8sCEL bool) RunnerOptions {
 	return func(r *Runner) {
 		r.useK8sCEL = useK8sCEL
@@ -144,7 +152,7 @@ func (r *Runner) runTest(ctx context.Context, suiteDir string, filter Filter, t
 }
 
 func (r *Runner) tryAddConstraint(ctx context.Context, suiteDir string, t *Test) error {
-	client, err := r.newClient(r.includeTrace, r.useK8sCEL)
+	client, err := r.newClient(r.includeTrace, r.printEnabled, r.useK8sCEL)
 	if err != nil {
 		return fmt.Errorf("%w: %w", gator.ErrCreatingClient, err)
 	}
@@ -213,7 +221,7 @@ func (r *Runner) skipCase(tc *Case) CaseResult {
 }
 
 func (r *Runner) makeTestClient(ctx context.Context, suiteDir string, t *Test) (gator.Client, error) {
-	client, err := r.newClient(r.includeTrace, r.useK8sCEL)
+	client, err := r.newClient(r.includeTrace, r.printEnabled, r.useK8sCEL)
 	if err != nil {
 		return nil, fmt.Errorf("%w: %w", gator.ErrCreatingClient, err)
 	}

pkg/gator/verify/runner_test.go

@@ -1268,7 +1268,7 @@ func TestRunner_Run_ClientError(t *testing.T) {
 		TestResults: []TestResult{{Error: gator.ErrCreatingClient}},
 	}
 
-	runner, err := NewRunner(fstest.MapFS{}, func(_ bool, _ bool) (gator.Client, error) {
+	runner, err := NewRunner(fstest.MapFS{}, func(_ bool, _ bool, _ bool) (gator.Client, error) {
 		return nil, errors.New("error")
 	})
 	if err != nil {