feat: implement "$patch: delete" logic

This PR implements "delete patches", same as in k8s.

Signed-off-by: Dmitriy Matrenichev <dmitry.matrenichev@siderolabs.com>

hack/release.toml

@@ -241,6 +241,13 @@ Extra announced endpoints can be added using the [`KubespanEndpointsConfig` docu
         title = "Machine Configuration via Kernel Command Line"
         description = """\
 Talos Linux supports supplying zstd-compressed, base64-encoded machine configuration small documents via the kernel command line parameter `talos.config.inline`.
+"""
+
+    [notes.patch-delete]
+        title = "Removing parts of the configuration using `$patch: delete` syntax"
+        description = """\
+Talos Linux now supports removing parts of the configuration using the `$patch: delete` syntax similar to the kubernetes.
+More information can be found [here](https://www.talos.dev/v1.8/talos-guides/configuration/patching/#strategic-merge-patches).
 """
 
 [make_deps]

pkg/machinery/config/configloader/configloader.go

@@ -21,15 +21,21 @@ import (
 var ErrNoConfig = errors.New("config not found")
 
 // newConfig initializes and returns a Configurator.
-func newConfig(r io.Reader) (config config.Provider, err error) {
+func newConfig(r io.Reader, opt ...Opt) (config config.Provider, err error) {
+	var opts Opts
+
+	for _, o := range opt {
+		o(&opts)
+	}
+
 	dec := decoder.NewDecoder()
 
 	var buf bytes.Buffer
 
 	// preserve the original contents
 	r = io.TeeReader(r, &buf)
 
-	manifests, err := dec.Decode(r)
+	manifests, err := dec.Decode(r, opts.allowPatchDelete)
 	if err != nil {
 		return nil, err
 	}
@@ -59,6 +65,30 @@ func NewFromStdin() (config.Provider, error) {
 }
 
 // NewFromBytes will take a byteslice and attempt to parse a config file from it.
-func NewFromBytes(source []byte) (config.Provider, error) {
-	return newConfig(bytes.NewReader(source))
+func NewFromBytes(source []byte, o ...Opt) (config.Provider, error) {
+	return newConfig(bytes.NewReader(source), o...)
+}
+
+// Opts represents the options for the config loader.
+type Opts struct {
+	allowPatchDelete bool
+}
+
+// Opt is a functional option for the config loader.
+type Opt func(*Opts)
+
+// WithAllowPatchDelete allows the loader to parse patch delete operations.
+func WithAllowPatchDelete() Opt {
+	return func(o *Opts) {
+		o.allowPatchDelete = true
+	}
 }
+
+// Selector represents a delete selector for a document.
+type Selector = decoder.Selector
+
+// ErrZeroedDocument is returned when the document is empty after applying the delete selector.
+var ErrZeroedDocument = decoder.ErrZeroedDocument
+
+// ErrLookupFailed is returned when the lookup failed.
+var ErrLookupFailed = decoder.ErrLookupFailed

pkg/machinery/config/configloader/internal/decoder/decoder.go

@@ -39,8 +39,8 @@ const (
 type Decoder struct{}
 
 // Decode decodes all known manifests.
-func (d *Decoder) Decode(r io.Reader) ([]config.Document, error) {
-	return parse(r)
+func (d *Decoder) Decode(r io.Reader, allowPatchDelete bool) ([]config.Document, error) {
+	return parse(r, allowPatchDelete)
 }
 
 // NewDecoder initializes and returns a `Decoder`.
@@ -54,7 +54,8 @@ type documentID struct {
 	Name       string
 }
 
-func parse(r io.Reader) (decoded []config.Document, err error) {
+//nolint:gocyclo
+func parse(r io.Reader, allowPatchDelete bool) (decoded []config.Document, err error) {
 	// Recover from yaml.v3 panics because we rely on machine configuration loading _a lot_.
 	defer func() {
 		if p := recover(); p != nil {
@@ -71,7 +72,7 @@ func parse(r io.Reader) (decoded []config.Document, err error) {
 	knownDocuments := map[documentID]struct{}{}
 
 	// Iterate through all defined documents.
-	for {
+	for i := 0; ; i++ {
 		var manifests yaml.Node
 
 		if err = dec.Decode(&manifests); err != nil {
@@ -86,6 +87,17 @@ func parse(r io.Reader) (decoded []config.Document, err error) {
 			return nil, errors.New("expected a document")
 		}
 
+		if allowPatchDelete {
+			decoded, err = AppendDeletesTo(&manifests, decoded, i)
+			if err != nil {
+				return nil, err
+			}
+
+			if manifests.IsZero() {
+				continue
+			}
+		}
+
 		for _, manifest := range manifests.Content {
 			id := documentID{
 				APIVersion: findValue(manifest, ManifestAPIVersionKey, false),
@@ -167,24 +179,3 @@ func decode(manifest *yaml.Node) (target config.Document, err error) {
 
 	return target, nil
 }
-
-func findValue(node *yaml.Node, key string, required bool) string {
-	if node.Kind != yaml.MappingNode {
-		panic(errors.New("expected a mapping node"))
-	}
-
-	for i := 0; i < len(node.Content)-1; i += 2 {
-		keyNode := node.Content[i]
-		val := node.Content[i+1]
-
-		if keyNode.Kind == yaml.ScalarNode && keyNode.Value == key {
-			return val.Value
-		}
-	}
-
-	if required {
-		panic(fmt.Errorf("missing '%s'", key))
-	}
-
-	return ""
-}

pkg/machinery/config/configloader/internal/decoder/decoder_test.go

@@ -311,7 +311,7 @@ config:
 			t.Parallel()
 
 			d := decoder.NewDecoder()
-			actual, err := d.Decode(bytes.NewReader(tt.source))
+			actual, err := d.Decode(bytes.NewReader(tt.source), false)
 
 			if tt.expected != nil {
 				assert.Equal(t, tt.expected, actual)
@@ -340,7 +340,7 @@ func TestDecoderV1Alpha1Config(t *testing.T) {
 			require.NoError(t, err)
 
 			d := decoder.NewDecoder()
-			_, err = d.Decode(bytes.NewReader(contents))
+			_, err = d.Decode(bytes.NewReader(contents), false)
 
 			assert.NoError(t, err)
 		})
@@ -354,7 +354,7 @@ func TestDoubleV1Alpha1(t *testing.T) {
 	contents := must.Value(files.ReadFile("v1alpha1.yaml"))(t)
 
 	d := decoder.NewDecoder()
-	_, err := d.Decode(bytes.NewReader(contents))
+	_, err := d.Decode(bytes.NewReader(contents), false)
 	require.Error(t, err)
 	require.ErrorContains(t, err, "not allowed")
 }
@@ -367,7 +367,7 @@ func BenchmarkDecoderV1Alpha1Config(b *testing.B) {
 
 	for range b.N {
 		d := decoder.NewDecoder()
-		_, err = d.Decode(bytes.NewReader(contents))
+		_, err = d.Decode(bytes.NewReader(contents), false)
 
 		assert.NoError(b, err)
 	}