add pkr plugin check cmd from packer core (#85)

This is simplified to not pull in core as a dep. The drawback is that we don't actually start plugins to verify that it works with Packer and has a ConfigSpec func. We do start a binary, though. But, I think this is fine since if a plugin implements describe then we can be pretty sure it uses the SDK's function and interfaces.

Related to hashicorp/packer#11317

closes hashicorp/packer#11309

cmd/packer-sdc/internal/plugincheck/README.md

@@ -0,0 +1,5 @@
+## `plugin-check`
+
+`plugin-check` will check wether a plugin binary seems to work with packer.
+
+Use: `packer-sdc plugin-check packer-plugin-happy-cloud`

cmd/packer-sdc/internal/plugincheck/cmd.go

@@ -0,0 +1,117 @@
+package plugincheck
+
+import (
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"log"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+var (
+	//go:embed README.md
+	readme string
+)
+
+type Command struct {
+}
+
+func (cmd *Command) Help() string {
+	return "\n" + readme
+}
+
+func (cmd *Command) Run(args []string) int {
+	if err := cmd.run(args); err != nil {
+		log.Printf("%v", err)
+		return 1
+	}
+	return 0
+}
+
+func (cmd *Command) run(args []string) error {
+
+	if len(args) != 1 {
+		cmd.Help()
+		return errors.New("plugin-check requires a plugin binary name as an argument.\n" +
+			"ex: 'packer-plugin-happycloud'. Check will be run on the binary.")
+	}
+
+	pluginName := args[0]
+
+	if isOldPlugin(pluginName) {
+		fmt.Printf("\n[WARNING] Plugin is named with old prefix `packer-[builder|provisioner|post-processor]-{name})`. " +
+			"These will be detected but Packer cannot install them automatically. " +
+			"The plugin must be a multi-component plugin named packer-plugin-{name} to be installable through the `packer init` command.\n" +
+			"See docs at: https://www.packer.io/docs/plugins.\n")
+		return nil
+	}
+
+	if err := checkPluginName(pluginName); err != nil {
+		return err
+	}
+
+	path, err := filepath.Abs(pluginName)
+	if err != nil {
+		return err
+	}
+
+	output, err := exec.Command(path, "describe").Output()
+	if err != nil {
+		return errors.Wrap(err, "failed to describe plugin")
+	}
+
+	desc := pluginDescription{}
+	err = json.Unmarshal(output, &desc)
+	if err != nil {
+		return errors.Wrap(err, "failed to json.Unmarshal plugin description")
+	}
+	if len(desc.Version) == 0 {
+		return errors.New("Version needs to be set")
+	}
+	if len(desc.SDKVersion) == 0 {
+		return errors.New("SDKVersion needs to be set")
+	}
+	if len(desc.APIVersion) == 0 {
+		return errors.New("APIVersion needs to be set")
+	}
+
+	if len(desc.Builders) == 0 && len(desc.PostProcessors) == 0 && len(desc.Datasources) == 0 {
+		return errors.New("this plugin defines no component.")
+	}
+	return nil
+}
+
+type pluginDescription struct {
+	Version        string   `json:"version"`
+	SDKVersion     string   `json:"sdk_version"`
+	APIVersion     string   `json:"api_version"`
+	Builders       []string `json:"builders"`
+	PostProcessors []string `json:"post_processors"`
+	Datasources    []string `json:"datasources"`
+}
+
+func isOldPlugin(pluginName string) bool {
+	return strings.HasPrefix(pluginName, "packer-builder-") ||
+		strings.HasPrefix(pluginName, "packer-provisioner-") ||
+		strings.HasPrefix(pluginName, "packer-post-processor-")
+}
+
+// checkPluginName checks for the possible valid names for a plugin,
+// packer-plugin-* or packer-[builder|provisioner|post-processor]-*. If the name
+// is prefixed with `packer-[builder|provisioner|post-processor]-`, packer won't
+// be able to install it, therefore a WARNING will be shown.
+func checkPluginName(name string) error {
+	if strings.HasPrefix(name, "packer-plugin-") {
+		return nil
+	}
+
+	return fmt.Errorf("plugin name is not valid")
+}
+
+func (cmd *Command) Synopsis() string {
+	return "Tell wether a plugin release looks valid for Packer."
+}

cmd/packer-sdc/main.go

@@ -6,6 +6,7 @@ import (
 	"os"
 
 	mapstructure_to_hcl2 "github.com/hashicorp/packer-plugin-sdk/cmd/packer-sdc/internal/mapstructure-to-hcl2"
+	"github.com/hashicorp/packer-plugin-sdk/cmd/packer-sdc/internal/plugincheck"
 	"github.com/hashicorp/packer-plugin-sdk/cmd/packer-sdc/internal/renderdocs"
 	struct_markdown "github.com/hashicorp/packer-plugin-sdk/cmd/packer-sdc/internal/struct-markdown"
 	"github.com/hashicorp/packer-plugin-sdk/version"
@@ -37,6 +38,9 @@ func main() {
 		"renderdocs": func() (cli.Command, error) {
 			return &renderdocs.Command{}, nil
 		},
+		"plugin-check": func() (cli.Command, error) {
+			return &plugincheck.Command{}, nil
+		},
 	}
 
 	exitStatus, err := c.Run()