fix: ship plugin.yaml in Helm 3 format for cross-version compatibility

go.mod

@@ -5,8 +5,10 @@ go 1.25.0
 require (
 	github.com/ghodss/yaml v1.0.0
 	github.com/spf13/cobra v1.10.2
+	go.yaml.in/yaml/v3 v3.0.4
 	helm.sh/helm/v3 v3.18.5
 	helm.sh/helm/v4 v4.1.0
+	sigs.k8s.io/yaml v1.6.0
 )
 
 require (
@@ -85,7 +87,6 @@ require (
 	github.com/xlab/treeprint v1.2.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.5.0 // indirect
 	go.yaml.in/yaml/v2 v2.4.3 // indirect
-	go.yaml.in/yaml/v3 v3.0.4 // indirect
 	golang.org/x/crypto v0.46.0 // indirect
 	golang.org/x/net v0.48.0 // indirect
 	golang.org/x/oauth2 v0.30.0 // indirect
@@ -117,5 +118,4 @@ require (
 	sigs.k8s.io/kustomize/kyaml v0.21.0 // indirect
 	sigs.k8s.io/randfill v1.0.0 // indirect
 	sigs.k8s.io/structured-merge-diff/v6 v6.3.1 // indirect
-	sigs.k8s.io/yaml v1.6.0 // indirect
 )

pkg/helm/plugin_manifest_test.go

@@ -0,0 +1,150 @@
+package helm
+
+import (
+	"bytes"
+	"os"
+	"testing"
+
+	v3plugin "helm.sh/helm/v3/pkg/plugin"
+	yamlv3 "go.yaml.in/yaml/v3"
+	sigsyaml "sigs.k8s.io/yaml"
+)
+
+// helmV4MetadataV1 mirrors Helm v4's internal MetadataV1 struct.
+// Helm v4 uses strict YAML parsing (KnownFields) for v1 manifests,
+// so any field not in this struct will cause an unmarshal error.
+type helmV4MetadataV1 struct {
+	APIVersion    string         `yaml:"apiVersion"`
+	Name          string         `yaml:"name"`
+	Type          string         `yaml:"type"`
+	Runtime       string         `yaml:"runtime"`
+	Version       string         `yaml:"version"`
+	SourceURL     string         `yaml:"sourceURL,omitempty"`
+	Config        map[string]any `yaml:"config"`
+	RuntimeConfig map[string]any `yaml:"runtimeConfig"`
+}
+
+// helmV4MetadataLegacy mirrors Helm v4's internal MetadataLegacy struct.
+// Helm v4 uses non-strict YAML parsing for legacy manifests (no apiVersion).
+type helmV4MetadataLegacy struct {
+	Name            string                          `yaml:"name"`
+	Version         string                          `yaml:"version"`
+	Usage           string                          `yaml:"usage"`
+	Description     string                          `yaml:"description"`
+	PlatformCommand []helmV4PlatformCommand          `yaml:"platformCommand"`
+	Command         string                          `yaml:"command"`
+	IgnoreFlags     bool                            `yaml:"ignoreFlags"`
+	PlatformHooks   map[string][]helmV4PlatformCommand `yaml:"platformHooks"`
+	Hooks           map[string]string               `yaml:"hooks"`
+	Downloaders     []helmV4Downloaders              `yaml:"downloaders"`
+}
+
+type helmV4PlatformCommand struct {
+	OperatingSystem string   `yaml:"os"`
+	Architecture    string   `yaml:"arch"`
+	Command         string   `yaml:"command"`
+	Args            []string `yaml:"args"`
+}
+
+type helmV4Downloaders struct {
+	Protocols []string `yaml:"protocols"`
+	Command   string   `yaml:"command"`
+}
+
+func TestPluginManifestHelm3Compatible(t *testing.T) {
+	// Helm 3 uses sigs.k8s.io/yaml.UnmarshalStrict which converts YAML to JSON
+	// and rejects unknown fields. This is the exact parsing path used by
+	// helm.sh/helm/v3/pkg/plugin.LoadDir().
+	files := map[string]string{
+		"plugin.yaml":              "../../plugin.yaml",
+		"testdata/plugin-helm3.yaml": "../../testdata/plugin-helm3.yaml",
+	}
+
+	for name, path := range files {
+		t.Run(name, func(t *testing.T) {
+			data, err := os.ReadFile(path)
+			if err != nil {
+				t.Fatalf("failed to read %s: %v", path, err)
+			}
+
+			var m v3plugin.Metadata
+			if err := sigsyaml.UnmarshalStrict(data, &m); err != nil {
+				t.Errorf("%s is not valid for Helm 3: %v", name, err)
+			}
+
+			if m.Name != "cm-push" {
+				t.Errorf("expected plugin name 'cm-push', got %q", m.Name)
+			}
+		})
+	}
+}
+
+func TestPluginManifestHelm4V1Compatible(t *testing.T) {
+	// Helm 4 uses go.yaml.in/yaml/v3 with KnownFields(true) for v1 manifests
+	// (those with apiVersion set). This rejects any YAML field not defined
+	// in MetadataV1. This is the exact parsing path used by
+	// helm.sh/helm/v4/internal/plugin.loadMetadataV1().
+	path := "../../testdata/plugin-helm4.yaml"
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("failed to read %s: %v", path, err)
+	}
+
+	var mv1 helmV4MetadataV1
+	d := yamlv3.NewDecoder(bytes.NewReader(data))
+	d.KnownFields(true)
+	if err := d.Decode(&mv1); err != nil {
+		t.Errorf("testdata/plugin-helm4.yaml is not valid for Helm 4 (v1 format): %v", err)
+	}
+
+	if mv1.Name != "cm-push" {
+		t.Errorf("expected plugin name 'cm-push', got %q", mv1.Name)
+	}
+	if mv1.APIVersion != "v1" {
+		t.Errorf("expected apiVersion 'v1', got %q", mv1.APIVersion)
+	}
+}
+
+func TestPluginManifestHelm4LegacyCompatible(t *testing.T) {
+	// Helm 4 supports legacy plugin manifests (no apiVersion field).
+	// It uses non-strict YAML parsing for these. The shipped plugin.yaml
+	// must be parseable by Helm 4's legacy loader since it's the first
+	// file Helm sees before the install hook can swap manifests.
+	// This is the exact parsing path used by
+	// helm.sh/helm/v4/internal/plugin.loadMetadataLegacy().
+	files := map[string]string{
+		"plugin.yaml":              "../../plugin.yaml",
+		"testdata/plugin-helm3.yaml": "../../testdata/plugin-helm3.yaml",
+	}
+
+	for name, path := range files {
+		t.Run(name, func(t *testing.T) {
+			data, err := os.ReadFile(path)
+			if err != nil {
+				t.Fatalf("failed to read %s: %v", path, err)
+			}
+
+			// Verify no apiVersion field (which would route to strict V1 parsing)
+			var peek struct {
+				APIVersion string `yaml:"apiVersion"`
+			}
+			if err := yamlv3.Unmarshal(data, &peek); err != nil {
+				t.Fatalf("failed to peek apiVersion: %v", err)
+			}
+			if peek.APIVersion != "" {
+				t.Errorf("%s has apiVersion=%q; shipped plugin.yaml must use legacy format (no apiVersion) for Helm 3/4 compatibility", name, peek.APIVersion)
+			}
+
+			// Parse as legacy (non-strict, matching Helm 4's loadMetadataLegacy)
+			var ml helmV4MetadataLegacy
+			d := yamlv3.NewDecoder(bytes.NewReader(data))
+			if err := d.Decode(&ml); err != nil {
+				t.Errorf("%s is not valid for Helm 4 legacy format: %v", name, err)
+			}
+
+			if ml.Name != "cm-push" {
+				t.Errorf("expected plugin name 'cm-push', got %q", ml.Name)
+			}
+		})
+	}
+}

plugin.yaml

@@ -1,20 +1,12 @@
 name: "cm-push"
 version: "0.11.0"
-apiVersion: v1
-type: cli/v1
-runtime: subprocess
-config:
-  usage: cm-push
-  shortHelp: Push chart package to ChartMuseum
-  longHelp: Helm plugin to push chart package to ChartMuseum
-runtimeConfig:
-  platformCommand:
-    - command: ${HELM_PLUGIN_DIR}/bin/helm-cm-push
+usage: "Please see https://github.com/chartmuseum/helm-push for usage"
+description: "Push chart package to ChartMuseum"
+command: "$HELM_PLUGIN_DIR/bin/helm-cm-push"
 downloaders:
   - command: "bin/helm-cm-push"
     protocols:
       - "cm"
-useTunnel: false
 hooks:
   install: "cd $HELM_PLUGIN_DIR; scripts/install_plugin.sh"
   update: "cd $HELM_PLUGIN_DIR; scripts/install_plugin.sh"

testdata/plugin-helm3.yaml

@@ -7,7 +7,6 @@ downloaders:
   - command: "bin/helm-cm-push"
     protocols:
       - "cm"
-useTunnel: false
 hooks:
   install: "cd $HELM_PLUGIN_DIR; scripts/install_plugin.sh"
   update: "cd $HELM_PLUGIN_DIR; scripts/install_plugin.sh"

testdata/plugin-helm4.yaml

@@ -10,11 +10,3 @@ config:
 runtimeConfig:
   platformCommand:
     - command: ${HELM_PLUGIN_DIR}/bin/helm-cm-push
-downloaders:
-  - command: "bin/helm-cm-push"
-    protocols:
-      - "cm"
-useTunnel: false
-hooks:
-  install: "cd $HELM_PLUGIN_DIR; scripts/install_plugin.sh"
-  update: "cd $HELM_PLUGIN_DIR; scripts/install_plugin.sh"