[notifiers/github] Truncate GitHub status if > 140 chars

Certain statuses are failing with the error:

```
description is too long (maximum is 140 characters)
```

This truncates and descriptions to 140 characters if they exceed the
limit.

notifiers/github-app/pkg/controller/status.go

@@ -20,21 +20,28 @@ func (r *GitHubAppReconciler) HandleStatus(ctx context.Context, tr *v1beta1.Task
 	repo := tr.Annotations[key("repo")]
 	commit := tr.Annotations[key("commit")]
 
-	var description *string
-	if m := tr.GetStatusCondition().GetCondition(apis.ConditionSucceeded).GetMessage(); m != "" {
-		description = github.String(m)
-	}
-
 	status := &github.RepoStatus{
 		State:       state(tr.Status),
-		Description: description,
+		Description: truncateDesc(tr.GetStatusCondition().GetCondition(apis.ConditionSucceeded).GetMessage()),
 		TargetURL:   github.String(dashboardURL(tr)),
 		Context:     github.String(tr.GetName()),
 	}
 	_, _, err = client.Repositories.CreateStatus(ctx, owner, repo, commit, status)
 	return err
 }
 
+// truncateDesc truncates a given string to fit within GitHub status character
+// limits (140 chars).
+func truncateDesc(m string) *string {
+	if m == "" {
+		return nil
+	}
+	if len(m) > 140 {
+		m = (m)[:137] + "..."
+	}
+	return &m
+}
+
 func dashboardURL(tr *v1beta1.TaskRun) string {
 	// TODO: generalize host, object type.
 	return fmt.Sprintf("https://dashboard.dogfooding.tekton.dev/#/namespaces/%s/taskruns/%s", tr.GetNamespace(), tr.GetName())

notifiers/github-app/pkg/controller/status_test.go

@@ -6,6 +6,8 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
+	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -69,3 +71,32 @@ func TestDashboardURL(t *testing.T) {
 		t.Errorf("want: %s, got: %s", want, got)
 	}
 }
+
+func TestTruncateDescription(t *testing.T) {
+	for _, tc := range []struct {
+		in   string
+		want *string
+	}{
+		{
+			in:   "",
+			want: nil,
+		},
+		{
+			in:   "~",
+			want: github.String("~"),
+		},
+		{
+			in:   strings.Repeat("~", 140),
+			want: github.String(strings.Repeat("~", 140)),
+		},
+		{
+			in:   strings.Repeat("~", 141),
+			want: github.String(strings.Repeat("~", 137) + "..."),
+		},
+	} {
+		out := truncateDesc(tc.in)
+		if !reflect.DeepEqual(out, tc.want) {
+			t.Errorf("truncDesc(%s) = %v, want %v", tc.in, out, tc.want)
+		}
+	}
+}