improve error message

This is the first step in attempting to read a Packer configuration file
via the packer init command. At the present moment it will try to read
one or more configuration templates from a given directory or path. Once
parsed it will error if parsing fails or exist successfully if it is
able to parse the file.

Looking at how the code is structured there will need to be changes made
to the following places:

- When no configuration file is found Packer will display an error. That
error should be bubbled up a bit so that the caller command can
determine if it should be displayed or not. For packer init no
configuration is not an error. Maybe it should be?

- After a configuration has been parsed there needs to be a single way
to determine a list of plugins associated with the configuration. HCL
and JSON configs have fields for this data but some is exported and some
is unexported. Adapting the packerHandler interface may be an option
here. More investigation needed.

command/cli.go

@@ -142,3 +142,18 @@ type HCL2UpgradeArgs struct {
 	MetaArgs
 	OutputFile string
 }
+
+func (ia *InitArgs) AddFlagSets(flags *flag.FlagSet) {
+	flags.StringVar(&ia.PluginDir, "plugin-dir", "", "")
+	flags.BoolVar(&ia.GetPlugins, "get-plugins", true, "")
+	flags.BoolVar(&ia.Upgrade, "upgrade", false, "")
+	ia.MetaArgs.AddFlagSets(flags)
+}
+
+//InitArgs respresents a parsed cli line for packer init
+type InitArgs struct {
+	MetaArgs
+	GetPlugins bool
+	PluginDir  string
+	Upgrade    bool
+}

command/init.go

@@ -0,0 +1,86 @@
+package command
+
+import (
+	"context"
+	"os"
+)
+
+// InitCommand initializes a Packer working directory.
+type InitCommand struct {
+	Meta
+}
+
+func (c *InitCommand) Run(args []string) int {
+	ctx, cleanup := handleTermInterrupt(c.Ui)
+	defer cleanup()
+
+	cla, ret := c.ParseArgs(args)
+	if ret != 0 {
+		return ret
+	}
+
+	return c.RunContext(ctx, cla)
+}
+
+func (c *InitCommand) ParseArgs(args []string) (*InitArgs, int) {
+	var cfg InitArgs
+	flags := c.Meta.FlagSet("init", FlagSetVars)
+	flags.Usage = func() { c.Ui.Say(c.Help()) }
+	cfg.AddFlagSets(flags)
+	if err := flags.Parse(args); err != nil {
+		return &cfg, 1
+	}
+
+	args = flags.Args()
+	if len(args) > 0 {
+		cfg.Path = args[0]
+	}
+
+	// Init command should treat an empty invocation as if it was run
+	// against the current working directory.
+	if cfg.Path == "" {
+		cfg.Path, _ = os.Getwd()
+	}
+
+	return &cfg, 0
+}
+
+func (c *InitCommand) RunContext(ctx context.Context, cla *InitArgs) int {
+
+	packerStarter, ret := c.GetConfig(&cla.MetaArgs)
+	if ret != 0 {
+		return ret
+	}
+
+	_ = packerStarter.Initialize()
+
+	return 0
+}
+
+func (c *InitCommand) Help() string {
+	helpText := `
+Usage: packer init [options]
+
+  Initialize a new or existing Packer working directory by downloading
+  builders, provisioners, and post-processors defined in the template.
+
+  This is the first command that should be executed when working with a new
+  or existing template. Running this command in an empty directory will
+  will perform no operation, and will need to be executed once a template
+  has been created to initialize the working directory.
+
+  It is safe to run init multiple times on a template to update the builders,
+  provisioners, post-processors with changes in the template configuration file.
+
+Options:
+  -get-plugins=false            Skips plugin installation.
+  -plugin-dir=PATH              Skips plugin installation and loads plugins only from the specified directory.
+  -upgrade=true                 Updates installed plugins to the latest available version.
+`
+	return helpText
+
+}
+
+func (c *InitCommand) Synopsis() string {
+	return "Initializes a Packer working directory"
+}

commands.go

@@ -64,5 +64,11 @@ func init() {
 				Meta: *CommandMeta,
 			}, nil
 		},
+
+		"init": func() (cli.Command, error) {
+			return &command.InitCommand{
+				Meta: *CommandMeta,
+			}, nil
+		},
 	}
 }

hcl2template/parser.go

@@ -71,9 +71,9 @@ func (p *Parser) Parse(filename string, varFiles []string, argVars map[string]st
 		if len(hclFiles)+len(jsonFiles) == 0 {
 			diags = append(diags, &hcl.Diagnostic{
 				Severity: hcl.DiagError,
-				Summary:  "Could not find any config file in " + filename,
+				Summary:  "No configuration files found in " + filename,
-				Detail: "A config file must be suffixed with `.pkr.hcl` or " +
+				Detail: "A valid configuration file must be present. Configuration \n" +
-					"`.pkr.json`. A folder can be referenced.",
+					"files must be suffixed with `.pkr.hcl` or `.pkr.json`.",
 			})
 		}
 		for _, filename := range hclFiles {