(feat): Add PluginConfig to the external plugins API:

Author: Copilot

docs/book/src/plugins/extending/external-plugins.md

@@ -26,10 +26,19 @@ standard I/O. Any language can be used to create the plugin, as long
 as it follows the [PluginRequest][code-plugin-external] and [PluginResponse][code-plugin-external]
 structures.
 
-### PluginRequest
-
 `PluginRequest` contains the data collected from the CLI and any previously executed plugins. Kubebuilder sends this data as a JSON object to the external plugin via `stdin`.
 
+**Fields:**
+- `apiVersion`: Version of the PluginRequest schema.
+- `args`: Command-line arguments passed to the plugin.
+- `command`: The subcommand being executed (e.g., `init`, `create api`, `create webhook`, `edit`).
+- `universe`: Map of file paths to contents, updated across the plugin chain.
+- `pluginChain` (optional): Array of plugin keys in the order they were executed. External plugins can inspect this to tailor behavior based on other plugins that ran (for example, `go.kubebuilder.io/v4` or `kustomize.common.kubebuilder.io/v2`).
+- `config` (optional): Serialized PROJECT file configuration for the current project. Use it to inspect metadata, existing resources, or plugin-specific settings. Kubebuilder omits this field before the PROJECT file exists—typically during the first `init`—so plugins should check for its presence.
+
+
+**Note:** Whenever Kubebuilder has a PROJECT file available (for example during `create api`, `create webhook`, `edit`, or a subsequent `init` run), `PluginRequest` includes the `config` field. During the very first `init` run the field is omitted because the PROJECT file does not exist yet.
+
 **Example `PluginRequest` (triggered by `kubebuilder init --plugins go/v4,sampleexternalplugin/v1 --domain my.domain`):**
 
 ```json
@@ -42,12 +51,25 @@ structures.
 }
 ```
 
-**Fields:**
-- `apiVersion`: Version of the PluginRequest schema.
-- `args`: Command-line arguments passed to the plugin.
-- `command`: The subcommand being executed (e.g., `init`, `create api`, `create webhook`, `edit`).
-- `universe`: Map of file paths to contents, updated across the plugin chain.
-- `pluginChain` (optional): Array of plugin keys in the chain. This allows external plugins to determine which other plugins are being used. For example, a plugin can check if `go.kubebuilder.io/v4` or `go.kubebuilder.io/v3` is in the chain to adjust its scaffolding accordingly.
+**Example `PluginRequest` for `create api` (includes `config`):**
+```json
+{
+  "apiVersion": "v1alpha1",
+  "args": ["--group", "crew", "--version", "v1", "--kind", "Captain"],
+  "command": "create api",
+  "universe": {},
+  "pluginChain": ["go.kubebuilder.io/v4", "kustomize.common.kubebuilder.io/v2", "sampleexternalplugin/v1"],
+  "config": {
+    "domain": "my.domain",
+    "repo": "github.com/example/my-project",
+    "projectName": "my-project",
+    "version": "3",
+    "layout": ["go.kubebuilder.io/v4"],
+    "multigroup": false,
+    "resources": []
+  }
+}
+```
 
 ### PluginResponse
 

pkg/cli/cli_test.go

@@ -77,6 +77,18 @@ func hasSubCommand(cmd *cobra.Command, name string) bool {
 	return false
 }
 
+type pluginChainCapturingSubcommand struct {
+	pluginChain []string
+}
+
+func (s *pluginChainCapturingSubcommand) Scaffold(machinery.Filesystem) error {
+	return nil
+}
+
+func (s *pluginChainCapturingSubcommand) SetPluginChain(chain []string) {
+	s.pluginChain = append([]string(nil), chain...)
+}
+
 var _ = Describe("CLI", func() {
 	var (
 		c              *CLI
@@ -431,6 +443,42 @@ plugins:
 		})
 	})
 
+	Context("applySubcommandHooks", func() {
+		var (
+			cmd        *cobra.Command
+			sub1, sub2 *pluginChainCapturingSubcommand
+			tuples     []keySubcommandTuple
+			chainKeys  []string
+		)
+
+		BeforeEach(func() {
+			cmd = &cobra.Command{}
+			sub1 = &pluginChainCapturingSubcommand{}
+			sub2 = &pluginChainCapturingSubcommand{}
+			tuples = []keySubcommandTuple{
+				{key: "alpha.kubebuilder.io/v1", subcommand: sub1},
+				{key: "beta.kubebuilder.io/v1", subcommand: sub2},
+			}
+			chainKeys = []string{"alpha.kubebuilder.io/v1", "beta.kubebuilder.io/v1"}
+		})
+
+		It("sets the plugin chain on subcommands", func() {
+			c.applySubcommandHooks(cmd, tuples, "test", false)
+
+			Expect(sub1.pluginChain).To(Equal(chainKeys))
+			Expect(sub2.pluginChain).To(Equal(chainKeys))
+		})
+
+		It("sets the plugin chain when creating a new configuration", func() {
+			c.resolvedPlugins = makeMockPluginsFor(projectVersion, chainKeys...)
+
+			c.applySubcommandHooks(cmd, tuples, "test", true)
+
+			Expect(sub1.pluginChain).To(Equal(chainKeys))
+			Expect(sub2.pluginChain).To(Equal(chainKeys))
+		})
+	})
+
 	Context("New", func() {
 		var c *CLI
 		var err error

pkg/cli/cmd_helpers.go

@@ -72,6 +72,10 @@ type keySubcommandTuple struct {
 	skip bool
 }
 
+type pluginChainSetter interface {
+	SetPluginChain([]string)
+}
+
 // filterSubcommands returns a list of plugin keys and subcommands from a filtered list of resolved plugins.
 func (c *CLI) filterSubcommands(
 	filter func(plugin.Plugin) bool,
@@ -107,6 +111,16 @@ func (c *CLI) applySubcommandHooks(
 	errorMessage string,
 	createConfig bool,
 ) {
+	commandPluginChain := make([]string, len(subcommands))
+	for i, tuple := range subcommands {
+		commandPluginChain[i] = tuple.key
+	}
+	for _, tuple := range subcommands {
+		if setter, ok := tuple.subcommand.(pluginChainSetter); ok {
+			setter.SetPluginChain(commandPluginChain)
+		}
+	}
+
 	// In case we create a new project configuration we need to compute the plugin chain.
 	pluginChain := make([]string, 0, len(c.resolvedPlugins))
 	if createConfig {

pkg/plugin/external/types.go

@@ -40,6 +40,10 @@ type PluginRequest struct {
 	// This allows external plugins to know which other plugins are in use.
 	// Format: ["go.kubebuilder.io/v4", "kustomize.common.kubebuilder.io/v2"]
 	PluginChain []string `json:"pluginChain,omitempty"`
+
+	// Config contains the PROJECT file config. This field may be empty if the
+	// project is being initialized and the PROJECT file has not been created yet.
+	Config map[string]interface{} `json:"config,omitempty"`
 }
 
 // PluginResponse is returned to kubebuilder by the plugin and contains all files

pkg/plugins/external/api.go

@@ -36,14 +36,33 @@ type createAPISubcommand struct {
 	Path        string
 	Args        []string
 	pluginChain []string
+	config      config.Config
 }
 
-// InjectConfig injects the project configuration to access plugin chain information
+// InjectConfig injects the project configuration so external plugins can read the PROJECT file.
 func (p *createAPISubcommand) InjectConfig(c config.Config) error {
-	p.pluginChain = c.GetPluginChain()
+	p.config = c
+
+	if c == nil {
+		return nil
+	}
+
+	if chain := c.GetPluginChain(); len(chain) > 0 {
+		p.pluginChain = append([]string(nil), chain...)
+	}
+
 	return nil
 }
 
+func (p *createAPISubcommand) SetPluginChain(chain []string) {
+	if len(chain) == 0 {
+		p.pluginChain = nil
+		return
+	}
+
+	p.pluginChain = append([]string(nil), chain...)
+}
+
 func (p *createAPISubcommand) InjectResource(*resource.Resource) error {
 	// Do nothing since resource flags are passed to the external plugin directly.
 	return nil
@@ -65,7 +84,7 @@ func (p *createAPISubcommand) Scaffold(fs machinery.Filesystem) error {
 		PluginChain: p.pluginChain,
 	}
 
-	err := handlePluginResponse(fs, req, p.Path)
+	err := handlePluginResponse(fs, req, p.Path, p.config)
 	if err != nil {
 		return err
 	}

pkg/plugins/external/edit.go

@@ -32,14 +32,33 @@ type editSubcommand struct {
 	Path        string
 	Args        []string
 	pluginChain []string
+	config      config.Config
 }
 
 // InjectConfig injects the project configuration to access plugin chain information
 func (p *editSubcommand) InjectConfig(c config.Config) error {
-	p.pluginChain = c.GetPluginChain()
+	p.config = c
+
+	if c == nil {
+		return nil
+	}
+
+	if chain := c.GetPluginChain(); len(chain) > 0 {
+		p.pluginChain = append([]string(nil), chain...)
+	}
+
 	return nil
 }
 
+func (p *editSubcommand) SetPluginChain(chain []string) {
+	if len(chain) == 0 {
+		p.pluginChain = nil
+		return
+	}
+
+	p.pluginChain = append([]string(nil), chain...)
+}
+
 func (p *editSubcommand) UpdateMetadata(_ plugin.CLIMetadata, subcmdMeta *plugin.SubcommandMetadata) {
 	setExternalPluginMetadata("edit", p.Path, subcmdMeta)
 }
@@ -56,7 +75,7 @@ func (p *editSubcommand) Scaffold(fs machinery.Filesystem) error {
 		PluginChain: p.pluginChain,
 	}
 
-	err := handlePluginResponse(fs, req, p.Path)
+	err := handlePluginResponse(fs, req, p.Path, p.config)
 	if err != nil {
 		return err
 	}