refactor: move list of allowed ResourceTemplate types to its own package

This will help reduce the number of places we keep track of the list of
types that Triggers can create especially as we add the v1beta1 types.

Partially addresses tektoncd#494 and part of the work needed for tektoncd#1067

pkg/apis/triggers/config/allowed_types.go

@@ -0,0 +1,30 @@
+package config
+
+import (
+	pipelinev1alpha1 "github.com/tektoncd/pipeline/pkg/apis/pipeline/v1alpha1"
+	pipelinev1beta1 "github.com/tektoncd/pipeline/pkg/apis/pipeline/v1beta1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/serializer"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
+)
+
+var Decoder runtime.Decoder
+
+// TODO(dibyom): We should have a way of configuring this instead of an init function?
+func init() {
+	scheme := runtime.NewScheme()
+	utilruntime.Must(pipelinev1alpha1.AddToScheme(scheme))
+	utilruntime.Must(pipelinev1beta1.AddToScheme(scheme))
+	codec := serializer.NewCodecFactory(scheme)
+	Decoder = codec.UniversalDecoder(
+		pipelinev1alpha1.SchemeGroupVersion,
+		pipelinev1beta1.SchemeGroupVersion,
+	)
+}
+
+// EnsureAllowedType returns nil if the resourceTemplate has an apiVersion
+// and kind field set to one of the allowed ones.
+func EnsureAllowedType(rt runtime.RawExtension) error {
+	_, err := runtime.Decode(Decoder, rt.Raw)
+	return err
+}

pkg/apis/triggers/v1alpha1/event_listener_validation_test.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"testing"
 
+	pipelinev1alpha1 "github.com/tektoncd/pipeline/pkg/apis/pipeline/v1alpha1"
 	"github.com/tektoncd/triggers/pkg/apis/triggers/v1alpha1"
 	"github.com/tektoncd/triggers/test"
 	bldr "github.com/tektoncd/triggers/test/builder"
@@ -274,6 +275,43 @@ func Test_EventListenerValidate(t *testing.T) {
 				},
 			},
 		},
+	}, {
+		name: "valid EventListener with embedded TriggerTemplate",
+		el: &v1alpha1.EventListener{
+			ObjectMeta: metav1.ObjectMeta{
+				Name:      "name",
+				Namespace: "namespace",
+			},
+			Spec: v1alpha1.EventListenerSpec{
+				Triggers: []v1alpha1.EventListenerTrigger{{
+					Bindings: []*v1alpha1.EventListenerBinding{{
+						Ref:        "tb",
+						Kind:       v1alpha1.NamespacedTriggerBindingKind,
+						APIVersion: "v1alpha1", // TODO: APIVersions seem wrong?
+					}},
+					Template: &v1alpha1.EventListenerTemplate{
+						Spec: &v1alpha1.TriggerTemplateSpec{
+							Params: []v1alpha1.ParamSpec{{
+								Name:        "foo",
+								Description: "desc",
+								Default:     ptr.String("val"),
+							}},
+							ResourceTemplates: []v1alpha1.TriggerResourceTemplate{{
+								RawExtension: test.RawExtension(t, pipelinev1alpha1.PipelineRun{
+									TypeMeta: metav1.TypeMeta{
+										APIVersion: "tekton.dev/v1alpha1",
+										Kind:       "TaskRun",
+									},
+									ObjectMeta: metav1.ObjectMeta{
+										Name: "$(tt.params.foo)",
+									},
+								}),
+							}},
+						},
+					},
+				}},
+			},
+		},
 	}}
 
 	for _, test := range tests {

pkg/apis/triggers/v1alpha1/trigger_template_types.go

@@ -82,10 +82,3 @@ type TriggerTemplateList struct {
 	metav1.ListMeta `json:"metadata,omitempty"`
 	Items           []TriggerTemplate `json:"items"`
 }
-
-// IsAllowedType returns true if the resourceTemplate has an apiVersion
-// and kind field set to one of the allowed ones.
-func (trt *TriggerResourceTemplate) IsAllowedType() error {
-	_, err := runtime.Decode(Decoder, trt.RawExtension.Raw)
-	return err
-}

pkg/apis/triggers/v1alpha1/trigger_template_validation.go

@@ -23,6 +23,7 @@ import (
 	"strings"
 
 	"github.com/tektoncd/pipeline/pkg/apis/validate"
+	"github.com/tektoncd/triggers/pkg/apis/triggers/config"
 	"k8s.io/apimachinery/pkg/api/equality"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/util/sets"
@@ -53,7 +54,7 @@ func (s *TriggerTemplateSpec) validate(ctx context.Context) (errs *apis.FieldErr
 
 func validateResourceTemplates(templates []TriggerResourceTemplate) (errs *apis.FieldError) {
 	for i, trt := range templates {
-		if err := trt.IsAllowedType(); err != nil {
+		if err := config.EnsureAllowedType(trt.RawExtension); err != nil {
 			if runtime.IsMissingVersion(err) {
 				errs = errs.Also(apis.ErrMissingField(fmt.Sprintf("[%d].apiVersion", i)))
 			}