Construct a default destination if one does not exist for service-router (#7783)

agent/consul/discoverychain/compile.go

@@ -552,7 +552,12 @@ func (c *compiler) assembleChain() error {
 		routeNode.Routes = append(routeNode.Routes, compiledRoute)
 
 		dest := route.Destination
-
+		if dest == nil {
+			dest = &structs.ServiceRouteDestination{
+				Service:   c.serviceName,
+				Namespace: router.NamespaceOrDefault(),
+			}
+		}
 		svc := defaultIfEmpty(dest.Service, c.serviceName)
 		destNamespace := defaultIfEmpty(dest.Namespace, router.NamespaceOrDefault())
 

agent/consul/discoverychain/compile_test.go

@@ -28,6 +28,7 @@ func TestCompile(t *testing.T) {
 		"router with defaults and resolver":                testcase_RouterWithDefaults_NoSplit_WithResolver(),
 		"router with defaults and noop split":              testcase_RouterWithDefaults_WithNoopSplit_DefaultResolver(),
 		"router with defaults and noop split and resolver": testcase_RouterWithDefaults_WithNoopSplit_WithResolver(),
+		"router with no destination":                       testcase_JustRouterWithNoDestination(),
 		"route bypasses splitter":                          testcase_RouteBypassesSplit(),
 		"noop split":                                       testcase_NoopSplit_DefaultResolver(),
 		"noop split with protocol from proxy defaults":     testcase_NoopSplit_DefaultResolver_ProtocolFromProxyDefaults(),
@@ -184,6 +185,68 @@ func testcase_JustRouterWithDefaults() compileTestCase {
 	return compileTestCase{entries: entries, expect: expect}
 }
 
+func testcase_JustRouterWithNoDestination() compileTestCase {
+	entries := newEntries()
+	setServiceProtocol(entries, "main", "http")
+
+	entries.AddRouters(
+		&structs.ServiceRouterConfigEntry{
+			Kind: "service-router",
+			Name: "main",
+			Routes: []structs.ServiceRoute{
+				{
+					Match: &structs.ServiceRouteMatch{
+						HTTP: &structs.ServiceRouteHTTPMatch{
+							PathPrefix: "/",
+						},
+					},
+				},
+			},
+		},
+	)
+
+	expect := &structs.CompiledDiscoveryChain{
+		Protocol:  "http",
+		StartNode: "router:main.default",
+		Nodes: map[string]*structs.DiscoveryGraphNode{
+			"router:main.default": &structs.DiscoveryGraphNode{
+				Type: structs.DiscoveryGraphNodeTypeRouter,
+				Name: "main.default",
+				Routes: []*structs.DiscoveryRoute{
+					{
+						Definition: &structs.ServiceRoute{
+							Match: &structs.ServiceRouteMatch{
+								HTTP: &structs.ServiceRouteHTTPMatch{
+									PathPrefix: "/",
+								},
+							},
+						},
+						NextNode: "resolver:main.default.dc1",
+					},
+					{
+						Definition: newDefaultServiceRoute("main", "default"),
+						NextNode:   "resolver:main.default.dc1",
+					},
+				},
+			},
+			"resolver:main.default.dc1": &structs.DiscoveryGraphNode{
+				Type: structs.DiscoveryGraphNodeTypeResolver,
+				Name: "main.default.dc1",
+				Resolver: &structs.DiscoveryResolver{
+					Default:        true,
+					ConnectTimeout: 5 * time.Second,
+					Target:         "main.default.dc1",
+				},
+			},
+		},
+		Targets: map[string]*structs.DiscoveryTarget{
+			"main.default.dc1": newTarget("main", "", "default", "dc1", nil),
+		},
+	}
+
+	return compileTestCase{entries: entries, expect: expect}
+}
+
 func testcase_RouterWithDefaults_NoSplit_WithResolver() compileTestCase {
 	entries := newEntries()
 	setServiceProtocol(entries, "main", "http")