rework source info access for plugin clients (#829)

#### What this PR does / why we need it:

Rework the plugin client interface to grant access to the source info
without exposing the complete internal cache information.

#### Which issue(s) this PR fixes:
<!--
Usage: `Fixes #<issue number>`, or `Fixes (paste link of issue)`.
-->

cmds/ocm/commands/ocmcmds/plugins/describe/describe.go

@@ -19,7 +19,7 @@ func DescribePlugin(p plugin.Plugin, out common.Printer) {
 	}
 	out.Printf("Status:           %s\n", "valid")
 	d := p.GetDescriptor()
-	src := p.GetInstallationInfo()
+	src := p.GetSourceInfo()
 	if src != nil && src.HasSourceInfo() {
 		out.Printf("Source:\n")
 		out.Printf("  Component:       %s\n", src.Component)

cmds/ocm/commands/ocmcmds/plugins/get/cmd.go

@@ -93,7 +93,7 @@ func getWide(opts *output.Options) output.Output {
 
 func mapGetRegularOutput(e interface{}) interface{} {
 	p := handler.Elem(e)
-	loc := p.GetInstallationInfo().GetInstallationSourceDescription()
+	loc := p.GetSourceInfo().GetDescription()
 
 	features := p.GetDescriptor().Capabilities()
 	return []string{p.Name(), p.Version(), loc, p.Message(), strings.Join(features, ",")}

cmds/subcmdplugin/cmds/cmd_test.go

@@ -69,7 +69,8 @@ Synopsis:
   ocm group demo <options> [flags]
 
 Flags:
-  -h, --help   help for demo
+  -h, --help             help for demo
+      --version string   some overloaded option
 
 Description:
   a demo command in a provided command group
@@ -111,7 +112,8 @@ Synopsis:
   ocm group demo <options> [flags]
 
 Flags:
-  -h, --help   help for demo
+  -h, --help             help for demo
+      --version string   some overloaded option
 
 Description:
   a demo command in a provided command group

cmds/subcmdplugin/cmds/demo/cmd.go

@@ -19,12 +19,16 @@ func New() *cobra.Command {
 		Long:  "a demo command in a provided command group",
 		RunE:  cmd.Run,
 	}
+
+	c.Flags().StringVarP(&cmd.version, "version", "", "", "some overloaded option")
 	return c
 }
 
-type command struct{}
+type command struct {
+	version string
+}
 
 func (c *command) Run(cmd *cobra.Command, args []string) error {
-	fmt.Printf("demo command called with arguments %v\n", args)
+	fmt.Printf("demo command called with arguments %v (and version option %s)\n", args, c.version)
 	return nil
 }

docs/command-plugins.md

@@ -41,18 +41,33 @@ func init() {
 
 #### CLI Commands
 
-CLI commands are simple configured `cobra.Command` objects.
-They are registered at the plugin object with
+CLI commands are provided by the registratuon interface `ppi.Command`. It
+provides some command metadata and a `cobra.Command` object.
 
+Commands are then registered at the plugin object with:
+
+```go
+    p.RegisterCommand(cmd)
 ```
-        cmd, err := clicmd.NewCLICommand(NewCommand(), clicmd.WithCLIConfig(), clicmd.WithVerb("check"))
-	if err != nil {
-		os.Exit(1)
-	}
-	p.RegisterCommand(NewCommand())
+
+The plugin programming interface supports the generation of an extension command directly from a
+`cobra.command` object using the method `NewCLICommand` from the `ppi.clicmd` package.
+It takes some options to specify the command embedding and extracts the other command attributes
+directly from the preconfigured cobra command.
+
+Otherwise, the `ppi.Command` interface  can be implemented without requiring a cobra command.
+
+A sample code could look like this:
+
+```go
+    cmd, err := clicmd.NewCLICommand(NewCommand(), clicmd.WithCLIConfig(), clicmd.WithVerb("check"))
+    if err != nil {
+        os.Exit(1)
+    }
+    p.RegisterCommand(cmd)
 ```
 
-with coding similar to
+with coding for the cobra command similar to
 
 ```
 
@@ -78,10 +93,6 @@ func (c *command) Run(cmd *cobra.Command, args []string) error {
 }
 ```
 
-The plugin programming interface supports the generation of an extension command directly from a
-cobra command object using the method `NewCLICommand` from the `ppi.clicmd` package.
-Otherwise the `ppi.Command` interface  can be implemented without requiring a cobra command..
-
 If the code wants to use the config framework, for example to
 - use the OCM library again
 - access credentials

pkg/contexts/ocm/plugin/cache/plugin.go

@@ -11,7 +11,7 @@ type Plugin = *pluginImpl
 // //nolint: errname // is no error.
 type pluginImpl struct {
 	name        string
-	source      *PluginInstallationInfo
+	info        *PluginInstallationInfo
 	descriptor  *descriptor.Descriptor
 	path        string
 	error       string
@@ -36,8 +36,14 @@ func NewPlugin(name string, path string, desc *descriptor.Descriptor, errmsg str
 	return p
 }
 
-func (p *pluginImpl) GetInstallationInfo() *PluginInstallationInfo {
-	return p.source
+func (p *pluginImpl) GetSourceInfo() *PluginSourceInfo {
+	if p.info == nil {
+		return nil
+	}
+	if p.info.HasSourceInfo() {
+		return &p.info.PluginSourceInfo
+	}
+	return nil
 }
 
 func (p *pluginImpl) GetDescriptor() *descriptor.Descriptor {

pkg/contexts/ocm/plugin/cache/plugindir.go

@@ -62,7 +62,7 @@ func (c *pluginDirImpl) add(name string, desc *descriptor.Descriptor, path strin
 			return
 		}
 
-		c.plugins[name].source = src
+		c.plugins[name].info = src
 	}
 	if errmsg != "" && list != nil {
 		list.Add(fmt.Errorf("%s: %s", name, errmsg))

pkg/contexts/ocm/plugin/cache/updater.go

@@ -41,20 +41,24 @@ type PluginSourceInfo struct {
 	Resource   string                     `json:"resource,omitempty"`
 }
 
-type PluginInstallationInfo struct {
-	PluginSourceInfo `json:",inline"`
-	PluginInfo       *PluginInfo `json:"info,omitempty"`
+func (p *PluginSourceInfo) HasSourceInfo() bool {
+	return p != nil && p.Repository != nil && p.Component != "" && p.Version != "" && p.Resource != ""
 }
 
-func (p *PluginInstallationInfo) GetInstallationSourceDescription() string {
+func (p *PluginSourceInfo) GetDescription() string {
 	if p != nil && p.HasSourceInfo() {
 		return p.Component + ":" + p.Version
 	}
 	return "local"
 }
 
+type PluginInstallationInfo struct {
+	PluginSourceInfo `json:",inline"`
+	PluginInfo       *PluginInfo `json:"info,omitempty"`
+}
+
 func (p *PluginInstallationInfo) HasSourceInfo() bool {
-	return p.Repository != nil && p.Component != "" && p.Version != "" && p.Resource != ""
+	return p != nil && p.PluginSourceInfo.HasSourceInfo()
 }
 
 func (p *PluginInstallationInfo) IsValidPluginInfo(execpath string) bool {

pkg/contexts/ocm/plugin/ppi/cmds/command/cmd.go

@@ -35,9 +35,14 @@ described by an access method descriptor (<CMD>` + p.Name() + ` descriptor</CMD>
 
 		nested := c.PreRunE
 		c.PreRunE = func(cmd *cobra.Command, args []string) error {
-			ctx, err := ConfigureFromFile(context.Background(), cliconfig)
-			if err != nil {
-				return err
+			var err error
+
+			ctx := context.Background()
+			if cliconfig != "" {
+				ctx, err = ConfigureFromFile(ctx, cliconfig)
+				if err != nil {
+					return err
+				}
 			}
 			c.SetContext(ctx)
 			if nested != nil {