support optional listMapKeys in server-side apply

[pohly]

What type of PR is this?

/kind feature

What this PR does / why we need it:

When an API uses +listType=map with a certain set of +listMapKeys, it should be possible to extend the API such that new, optional fields can be used as keys. This used to fail with associative list with keys has an element that omits key field "shareUID" (and doesn''t have default value) for a new key shareUID. As of structured-merged-diff v6.3.0 it's supported, see kubernetes-sigs/structured-merge-diff#296 (merged via kubernetes-sigs/structured-merge-diff#298).

Also includes an integration test for SSA with such an optional key.

Which issue(s) this PR is related to:

Fixes #132524

Special notes for your reviewer:

Based on #132998, which in turn was based on my branch.

Diff against #132998 is just some test and commit message cleanup:

diff --git a/test/integration/apimachinery/apply/apply_test.go b/test/integration/apimachinery/apply/apply_test.go
index 204e2234a04..ce51b5299a5 100644
--- a/test/integration/apimachinery/apply/apply_test.go
+++ b/test/integration/apimachinery/apply/apply_test.go
@@ -46,49 +46,40 @@ func init() {
 }
 
 func TestApply(t *testing.T) {
-	// Each sub-test brings up the API server in a certain  configuration.
-	for name, tc := range map[string]struct {
-		extendedTestGroupAPI bool
-		f                    func(tCtx ktesting.TContext)
-	}{
-		"upgrade": {
-			f: func(tCtx ktesting.TContext) {
-				tCtx.Run("", func(tCtx ktesting.TContext) { testApply(tCtx, false) })
-			},
-		},
-	} {
-		t.Run(name, func(t *testing.T) {
-			tCtx := ktesting.Init(t)
-			etcdOptions := framework.SharedEtcd()
-			apiServerOptions := kubeapiservertesting.NewDefaultTestServerOptions()
-			apiServerFlags := framework.DefaultTestServerFlags()
-			runtimeConfigs := []string{"testapigroup.apimachinery.k8s.io/v1=true"}
-			apiServerFlags = append(apiServerFlags, "--runtime-config="+strings.Join(runtimeConfigs, ","))
-
-			if controlplane.AdditionalStorageProvidersForTests != nil {
-				t.Fatal("cannot set AdditionalStorageProvidersForTests, already set")
-			}
-			t.Cleanup(func() {
-				controlplane.AdditionalStorageProvidersForTests = nil
-			})
-			controlplane.AdditionalStorageProvidersForTests = func(client *kubernetes.Clientset) []controlplaneapiserver.RESTStorageProvider {
-				return []controlplaneapiserver.RESTStorageProvider{
-					testapigrouprest.RESTStorageProvider{NamespaceClient: client.CoreV1().Namespaces()},
-				}
-			}
-
-			server := kubeapiservertesting.StartTestServerOrDie(t, apiServerOptions, apiServerFlags, etcdOptions)
-			tCtx.CleanupCtx(func(tCtx ktesting.TContext) {
-				tCtx.Log("Stopping the apiserver...")
-				server.TearDownFn()
-			})
-			tCtx = ktesting.WithRESTConfig(tCtx, server.ClientConfig)
-			tc.f(tCtx)
-		})
+	tCtx := ktesting.Init(t)
+	etcdOptions := framework.SharedEtcd()
+	apiServerOptions := kubeapiservertesting.NewDefaultTestServerOptions()
+	apiServerFlags := framework.DefaultTestServerFlags()
+	runtimeConfigs := []string{"testapigroup.apimachinery.k8s.io/v1=true"}
+	apiServerFlags = append(apiServerFlags, "--runtime-config="+strings.Join(runtimeConfigs, ","))
+
+	// Sanity check. Not protected against concurrent access, but that's
+	// okay: integration tests are also run with race detection, so that
+	// would catch it.
+	if controlplane.AdditionalStorageProvidersForTests != nil {
+		t.Fatal("cannot set AdditionalStorageProvidersForTests, already set")
+	}
+	t.Cleanup(func() {
+		controlplane.AdditionalStorageProvidersForTests = nil
+	})
+	controlplane.AdditionalStorageProvidersForTests = func(client *kubernetes.Clientset) []controlplaneapiserver.RESTStorageProvider {
+		return []controlplaneapiserver.RESTStorageProvider{
+			testapigrouprest.RESTStorageProvider{NamespaceClient: client.CoreV1().Namespaces()},
+		}
 	}
+
+	server := kubeapiservertesting.StartTestServerOrDie(t, apiServerOptions, apiServerFlags, etcdOptions)
+	tCtx.CleanupCtx(func(tCtx ktesting.TContext) {
+		tCtx.Log("Stopping the apiserver...")
+		server.TearDownFn()
+	})
+	tCtx = ktesting.WithRESTConfig(tCtx, server.ClientConfig)
+
+	// More sub-tests could be added here. Currently there's only one.
+	tCtx.Run("optional-list-map-key", testOptionalListMapKey)
 }
 
-func testApply(tCtx ktesting.TContext, upgrade bool) {
+func testOptionalListMapKey(tCtx ktesting.TContext) {
 	requireManagedFields := func(what string, obj *unstructured.Unstructured, expectedManagedFields any) {
 		tCtx.Helper()
 		actualManagedFields, _, _ := unstructured.NestedFieldCopy(obj.Object, "metadata", "managedFields")

Does this PR introduce a user-facing change?

NONE

/assign @jpbetz @liggitt

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[liggitt]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 0a7b0eaf56c33f5bfd88b904fc0fbde6b0fa1ff9

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt, pohly

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