Fall back to numeric id in project URLs

ProjectUrl built projects/<identifier> with no fallback, so a project
whose identifier is empty produced projects/ (the index) instead of
the project. Mirror WorkPackageUrl and use the numeric id, which is
also a valid /projects/ address, when the identifier is missing.

Author: myabc

components/routes/routes.go

@@ -28,6 +28,12 @@ func WorkPackageUrl(workPackage *models.WorkPackage) *url.URL {
 
 func ProjectUrl(project *models.Project) *url.URL {
 	routeUrl := *host
-	routeUrl.Path = fmt.Sprintf("projects/%s", project.Identifier)
+	// Current servers always set identifier, but fall back to the numeric id
+	// (also a valid /projects/ address) when it is missing.
+	identifier := project.Identifier
+	if identifier == "" {
+		identifier = strconv.FormatUint(project.Id, 10)
+	}
+	routeUrl.Path = fmt.Sprintf("projects/%s", identifier)
 	return &routeUrl
 }

components/routes/routes_test.go

@@ -0,0 +1,40 @@
+package routes_test
+
+import (
+	"net/url"
+	"testing"
+
+	"github.com/opf/openproject-cli/components/routes"
+	"github.com/opf/openproject-cli/models"
+)
+
+func initHost(t *testing.T) {
+	t.Helper()
+	host, err := url.Parse("https://op.example.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+	routes.Init(host)
+}
+
+func TestProjectUrl_UsesIdentifierWhenPresent(t *testing.T) {
+	initHost(t)
+
+	got := routes.ProjectUrl(&models.Project{Id: 42, Identifier: "my-project"}).String()
+	want := "https://op.example.com/projects/my-project"
+	if got != want {
+		t.Errorf("ProjectUrl = %q, want %q", got, want)
+	}
+}
+
+// A project whose identifier is missing (older servers, minimal payloads) must
+// still produce a working URL by falling back to the numeric id.
+func TestProjectUrl_EmptyIdentifierFallsBackToId(t *testing.T) {
+	initHost(t)
+
+	got := routes.ProjectUrl(&models.Project{Id: 42, Identifier: ""}).String()
+	want := "https://op.example.com/projects/42"
+	if got != want {
+		t.Errorf("ProjectUrl = %q, want %q", got, want)
+	}
+}