packer console for HCL2 (#9359)

command/build.go

@@ -58,14 +58,13 @@ func (c *BuildCommand) ParseArgs(args []string) (*BuildArgs, int) {
 	return &cfg, 0
 }
 
-func (m *Meta) GetConfigFromHCL(cla *MetaArgs) (packer.BuildGetter, int) {
+func (m *Meta) GetConfigFromHCL(cla *MetaArgs) (*hcl2template.PackerConfig, int) {
 	parser := &hcl2template.Parser{
 		Parser:                hclparse.NewParser(),
 		BuilderSchemas:        m.CoreConfig.Components.BuilderStore,
 		ProvisionersSchemas:   m.CoreConfig.Components.ProvisionerStore,
 		PostProcessorsSchemas: m.CoreConfig.Components.PostProcessorStore,
 	}
-
 	cfg, diags := parser.Parse(cla.Path, cla.VarFiles, cla.Vars)
 	return cfg, writeDiags(m.Ui, parser.Files(), diags)
 }
@@ -88,15 +87,15 @@ func writeDiags(ui packer.Ui, files map[string]*hcl.File, diags hcl.Diagnostics)
 	return 0
 }
 
-func (m *Meta) GetConfig(cla *MetaArgs) (packer.BuildGetter, int) {
+func (m *Meta) GetConfig(cla *MetaArgs) (packer.Handler, int) {
-	cfgType, err := ConfigType(cla.Path)
+	cfgType, err := cla.GetConfigType()
 	if err != nil {
-		m.Ui.Error(fmt.Sprintf("could not tell config type: %s", err))
+		m.Ui.Error(fmt.Sprintf("%q: %s", cla.Path, err))
 		return nil, 1
 	}
 
 	switch cfgType {
-	case "hcl":
+	case ConfigTypeHCL2:
 		// TODO(azr): allow to pass a slice of files here.
 		return m.GetConfigFromHCL(cla)
 	default:
@@ -110,9 +109,18 @@ func (m *Meta) GetConfig(cla *MetaArgs) (packer.BuildGetter, int) {
 	}
 }
 
-func (m *Meta) GetConfigFromJSON(cla *MetaArgs) (packer.BuildGetter, int) {
+func (m *Meta) GetConfigFromJSON(cla *MetaArgs) (*packer.Core, int) {
 	// Parse the template
-	tpl, err := template.ParseFile(cla.Path)
+	var tpl *template.Template
+	var err error
+	if cla.Path == "" {
+		// here cla validation passed so this means we want a default builder
+		// and we probably are in the console command
+		tpl, err = template.Parse(TiniestBuilder)
+	} else {
+		tpl, err = template.ParseFile(cla.Path)
+	}
+
 	if err != nil {
 		m.Ui.Error(fmt.Sprintf("Failed to parse template: %s", err))
 		return nil, 1

command/cli.go

@@ -2,7 +2,6 @@ package command
 
 import (
 	"flag"
-	"fmt"
 	"strings"
 
 	"github.com/hashicorp/packer/helper/enumflag"
@@ -10,32 +9,44 @@ import (
 	sliceflag "github.com/hashicorp/packer/helper/flag-slice"
 )
 
+//go:generate enumer -type configType -trimprefix ConfigType -transform snake
+type configType int
+
+const (
+	ConfigTypeJSON configType = iota // default config type
+	ConfigTypeHCL2
+)
+
+func (c *configType) Set(value string) error {
+	v, err := configTypeString(value)
+	if err == nil {
+		*c = v
+	}
+	return err
+}
+
 // ConfigType tells what type of config we should use, it can return values
 // like "hcl" or "json".
 // Make sure Args was correctly set before.
-func ConfigType(args ...string) (string, error) {
+func (ma *MetaArgs) GetConfigType() (configType, error) {
-	switch len(args) {
+	if ma.Path == "" {
-	// TODO(azr): in the future, I want to allow passing multiple arguments to
+		return ma.ConfigType, nil
-	// merge HCL confs together; but this will probably need an RFC first.
+	}
-	case 1:
+	name := ma.Path
-		name := args[0]
 	if name == "-" {
 		// TODO(azr): To allow piping HCL2 confs (when args is "-"), we probably
 		// will need to add a setting that says "this is an HCL config".
-			return "json", nil
+		return ma.ConfigType, nil
 	}
 	if strings.HasSuffix(name, ".pkr.hcl") ||
 		strings.HasSuffix(name, ".pkr.json") {
-			return "hcl", nil
+		return ConfigTypeHCL2, nil
 	}
 	isDir, err := isDir(name)
 	if isDir {
-			return "hcl", err
+		return ConfigTypeHCL2, err
-		}
-		return "json", err
-	default:
-		return "", fmt.Errorf("packer only takes one argument: %q", args)
 	}
+	return ma.ConfigType, err
 }
 
 // NewMetaArgs parses cli args and put possible values
@@ -44,14 +55,19 @@ func (ma *MetaArgs) AddFlagSets(fs *flag.FlagSet) {
 	fs.Var((*sliceflag.StringFlag)(&ma.Except), "except", "")
 	fs.Var((*kvflag.Flag)(&ma.Vars), "var", "")
 	fs.Var((*kvflag.StringSlice)(&ma.VarFiles), "var-file", "")
+	fs.Var(&ma.ConfigType, "config-type", "set to 'hcl2' to run in hcl2 mode when no file is passed.")
 }
 
 // MetaArgs defines commonalities between all comands
 type MetaArgs struct {
+	// TODO(azr): in the future, I want to allow passing multiple path to
+	// merge HCL confs together; but this will probably need an RFC first.
 	Path         string
 	Only, Except []string
 	Vars         map[string]string
 	VarFiles     []string
+	// set to "hcl2" to force hcl2 mode
+	ConfigType configType
 }
 
 func (ba *BuildArgs) AddFlagSets(flags *flag.FlagSet) {
@@ -78,7 +94,9 @@ type BuildArgs struct {
 }
 
 // ConsoleArgs represents a parsed cli line for a `packer console`
-type ConsoleArgs struct{ MetaArgs }
+type ConsoleArgs struct {
+	MetaArgs
+}
 
 func (fa *FixArgs) AddFlagSets(flags *flag.FlagSet) {
 	flags.BoolVar(&fa.Validate, "validate", true, "")

command/configtype_enumer.go

@@ -0,0 +1,50 @@
+// Code generated by "enumer -type configType -trimprefix ConfigType -transform snake"; DO NOT EDIT.
+
+//
+package command
+
+import (
+	"fmt"
+)
+
+const _configTypeName = "jsonhcl2"
+
+var _configTypeIndex = [...]uint8{0, 4, 8}
+
+func (i configType) String() string {
+	if i < 0 || i >= configType(len(_configTypeIndex)-1) {
+		return fmt.Sprintf("configType(%d)", i)
+	}
+	return _configTypeName[_configTypeIndex[i]:_configTypeIndex[i+1]]
+}
+
+var _configTypeValues = []configType{0, 1}
+
+var _configTypeNameToValueMap = map[string]configType{
+	_configTypeName[0:4]: 0,
+	_configTypeName[4:8]: 1,
+}
+
+// configTypeString retrieves an enum value from the enum constants string name.
+// Throws an error if the param is not part of the enum.
+func configTypeString(s string) (configType, error) {
+	if val, ok := _configTypeNameToValueMap[s]; ok {
+		return val, nil
+	}
+	return 0, fmt.Errorf("%s does not belong to configType values", s)
+}
+
+// configTypeValues returns all values of the enum
+func configTypeValues() []configType {
+	return _configTypeValues
+}
+
+// IsAconfigType returns "true" if the value is listed in the enum definition. "false" otherwise
+func (i configType) IsAconfigType() bool {
+	for _, v := range _configTypeValues {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}

command/console.go

@@ -3,7 +3,6 @@ package command
 import (
 	"bufio"
 	"context"
-	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -12,19 +11,17 @@ import (
 	"github.com/hashicorp/packer/helper/wrappedreadline"
 	"github.com/hashicorp/packer/helper/wrappedstreams"
 	"github.com/hashicorp/packer/packer"
-	"github.com/hashicorp/packer/template"
-	"github.com/hashicorp/packer/template/interpolate"
 	"github.com/posener/complete"
 )
 
-const TiniestBuilder = `{
+var TiniestBuilder = strings.NewReader(`{
 	"builders": [
 		{
 			"type":"null",
 			"communicator": "none"
 		}
 	]
-}`
+}`)
 
 type ConsoleCommand struct {
 	Meta
@@ -51,49 +48,24 @@ func (c *ConsoleCommand) ParseArgs(args []string) (*ConsoleArgs, int) {
 	}
 
 	args = flags.Args()
+	if len(args) == 1 {
+		cfg.Path = args[0]
+	}
 	return &cfg, 0
 }
 
 func (c *ConsoleCommand) RunContext(ctx context.Context, cla *ConsoleArgs) int {
-
+	packerStarter, ret := c.GetConfig(&cla.MetaArgs)
-	var templ *template.Template
+	if ret != 0 {
-	if cla.Path == "" {
+		return ret
-		// If user has not defined a builder, create a tiny null placeholder
-		// builder so that we can properly initialize the core
-		tpl, err := template.Parse(strings.NewReader(TiniestBuilder))
-		if err != nil {
-			c.Ui.Error(fmt.Sprintf("Failed to generate placeholder template: %s", err))
-			return 1
-		}
-		templ = tpl
-	} else {
-		// Parse the provided template
-		tpl, err := template.ParseFile(cla.Path)
-		if err != nil {
-			c.Ui.Error(fmt.Sprintf("Failed to parse template: %s", err))
-			return 1
-		}
-		templ = tpl
-	}
-
-	// Get the core
-	core, err := c.Meta.Core(templ, &cla.MetaArgs)
-	if err != nil {
-		c.Ui.Error(err.Error())
-		return 1
-	}
-
-	// IO Loop
-	session := &REPLSession{
-		Core: core,
 	}
 
 	// Determine if stdin is a pipe. If so, we evaluate directly.
 	if c.StdinPiped() {
-		return c.modePiped(session)
+		return c.modePiped(packerStarter)
 	}
 
-	return c.modeInteractive(session)
+	return c.modeInteractive(packerStarter)
 }
 
 func (*ConsoleCommand) Help() string {
@@ -128,13 +100,14 @@ func (*ConsoleCommand) AutocompleteFlags() complete.Flags {
 	}
 }
 
-func (c *ConsoleCommand) modePiped(session *REPLSession) int {
+func (c *ConsoleCommand) modePiped(cfg packer.Evaluator) int {
 	var lastResult string
 	scanner := bufio.NewScanner(wrappedstreams.Stdin())
+	ret := 0
 	for scanner.Scan() {
-		result, err := session.Handle(strings.TrimSpace(scanner.Text()))
+		result, _, diags := cfg.EvaluateExpression(strings.TrimSpace(scanner.Text()))
-		if err != nil {
+		if len(diags) > 0 {
-			return 0
+			ret = writeDiags(c.Ui, nil, diags)
 		}
 		// Store the last result
 		lastResult = result
@@ -142,10 +115,11 @@ func (c *ConsoleCommand) modePiped(session *REPLSession) int {
 
 	// Output the final result
 	c.Ui.Message(lastResult)
-	return 0
+	return ret
 }
 
-func (c *ConsoleCommand) modeInteractive(session *REPLSession) int { // Setup the UI so we can output directly to stdout
+func (c *ConsoleCommand) modeInteractive(cfg packer.Evaluator) int {
+	// Setup the UI so we can output directly to stdout
 	l, err := readline.NewEx(wrappedreadline.Override(&readline.Config{
 		Prompt:            "> ",
 		InterruptPrompt:   "^C",
@@ -170,76 +144,16 @@ func (c *ConsoleCommand) modeInteractive(session *REPLSession) int { // Setup th
 		} else if err == io.EOF {
 			break
 		}
-		out, err := session.Handle(line)
+		out, exit, diags := cfg.EvaluateExpression(line)
-		if err == ErrSessionExit {
+		ret := writeDiags(c.Ui, nil, diags)
-			break
+		if exit {
+			return ret
 		}
-		if err != nil {
-			c.Ui.Error(err.Error())
-			continue
-		}
-
 		c.Ui.Say(out)
+		if exit {
+			return ret
+		}
 	}
 
 	return 0
 }
-
-// ErrSessionExit is a special error result that should be checked for
-// from Handle to signal a graceful exit.
-var ErrSessionExit = errors.New("Session exit")
-
-// Session represents the state for a single Read-Evaluate-Print-Loop (REPL) session.
-type REPLSession struct {
-	// Core is used for constructing interpolations based off packer templates
-	Core *packer.Core
-}
-
-// Handle a single line of input from the REPL.
-//
-// The return value is the output and the error to show.
-func (s *REPLSession) Handle(line string) (string, error) {
-	switch {
-	case strings.TrimSpace(line) == "":
-		return "", nil
-	case strings.TrimSpace(line) == "exit":
-		return "", ErrSessionExit
-	case strings.TrimSpace(line) == "help":
-		return s.handleHelp()
-	case strings.TrimSpace(line) == "variables":
-		return s.handleVariables()
-	default:
-		return s.handleEval(line)
-	}
-}
-
-func (s *REPLSession) handleEval(line string) (string, error) {
-	ctx := s.Core.Context()
-	rendered, err := interpolate.Render(line, ctx)
-	if err != nil {
-		return "", fmt.Errorf("Error interpolating: %s", err)
-	}
-	return rendered, nil
-}
-
-func (s *REPLSession) handleVariables() (string, error) {
-	varsstring := "\n"
-	for k, v := range s.Core.Context().UserVariables {
-		varsstring += fmt.Sprintf("%s: %+v,\n", k, v)
-	}
-
-	return varsstring, nil
-}
-
-func (s *REPLSession) handleHelp() (string, error) {
-	text := `
-The Packer console allows you to experiment with Packer interpolations.
-You may access variables in the Packer config you called the console with.
-
-Type in the interpolation to test and hit <enter> to see the result.
-
-To exit the console, type "exit" and hit <enter>, or use Control-C.
-`
-
-	return strings.TrimSpace(text), nil
-}

command/console_test.go

@@ -0,0 +1,42 @@
+package command
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/hashicorp/packer/hcl2template"
+	"github.com/hashicorp/packer/packer"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_piping(t *testing.T) {
+
+	tc := []struct {
+		piped    string
+		command  []string
+		env      []string
+		expected string
+	}{
+		{"help", []string{"console"}, nil, packer.ConsoleHelp + "\n"},
+		{"help", []string{"console", "--config-type=hcl2"}, nil, hcl2template.PackerConsoleHelp + "\n"},
+		{"var.fruit", []string{"console", filepath.Join(testFixture("var-arg"), "fruit_builder.pkr.hcl")}, []string{"PKR_VAR_fruit=potato"}, "potato\n"},
+		{"upper(var.fruit)", []string{"console", filepath.Join(testFixture("var-arg"), "fruit_builder.pkr.hcl")}, []string{"PKR_VAR_fruit=potato"}, "POTATO\n"},
+		{"1 + 5", []string{"console", "--config-type=hcl2"}, nil, "6\n"},
+		{"var.images", []string{"console", filepath.Join(testFixture("var-arg"), "map.pkr.hcl")}, nil, "{\n" + `  "key" = "value"` + "\n}\n"},
+	}
+
+	for _, tc := range tc {
+		t.Run(fmt.Sprintf("echo %q | packer %s", tc.piped, tc.command), func(t *testing.T) {
+			p := helperCommand(t, tc.command...)
+			p.Stdin = strings.NewReader(tc.piped)
+			p.Env = append(p.Env, tc.env...)
+			bs, err := p.Output()
+			if err != nil {
+				t.Fatalf("%v: %s", err, bs)
+			}
+			assert.Equal(t, tc.expected, string(bs))
+		})
+	}
+}

command/exec_test.go

@@ -0,0 +1,127 @@
+package command
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"runtime"
+	"testing"
+
+	"github.com/hashicorp/packer/builder/file"
+	"github.com/hashicorp/packer/builder/null"
+	"github.com/hashicorp/packer/packer"
+	"github.com/hashicorp/packer/post-processor/manifest"
+	shell_local_pp "github.com/hashicorp/packer/post-processor/shell-local"
+	filep "github.com/hashicorp/packer/provisioner/file"
+	"github.com/hashicorp/packer/provisioner/shell"
+	shell_local "github.com/hashicorp/packer/provisioner/shell-local"
+	"github.com/hashicorp/packer/version"
+)
+
+// HasExec reports whether the current system can start new processes
+// using os.StartProcess or (more commonly) exec.Command.
+func HasExec() bool {
+	switch runtime.GOOS {
+	case "js":
+		return false
+	case "darwin":
+		if runtime.GOARCH == "arm64" {
+			return false
+		}
+	}
+	return true
+}
+
+// MustHaveExec checks that the current system can start new processes
+// using os.StartProcess or (more commonly) exec.Command.
+// If not, MustHaveExec calls t.Skip with an explanation.
+func MustHaveExec(t testing.TB) {
+	if !HasExec() {
+		t.Skipf("skipping test: cannot exec subprocess on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+func helperCommandContext(t *testing.T, ctx context.Context, s ...string) (cmd *exec.Cmd) {
+	MustHaveExec(t)
+
+	cs := []string{"-test.run=TestHelperProcess", "--"}
+	cs = append(cs, s...)
+	if ctx != nil {
+		cmd = exec.CommandContext(ctx, os.Args[0], cs...)
+	} else {
+		cmd = exec.Command(os.Args[0], cs...)
+	}
+	cmd.Env = append(os.Environ(), "GO_WANT_HELPER_PROCESS=1")
+	return cmd
+}
+
+func helperCommand(t *testing.T, s ...string) *exec.Cmd {
+	return helperCommandContext(t, nil, s...)
+}
+
+// TestHelperProcess isn't a real test. It's used as a helper process
+// for TestParameterRun.
+func TestHelperProcess(*testing.T) {
+	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
+		return
+	}
+	defer os.Exit(0)
+
+	args := os.Args
+	for len(args) > 0 {
+		if args[0] == "--" {
+			args = args[1:]
+			break
+		}
+		args = args[1:]
+	}
+	if len(args) == 0 {
+		fmt.Fprintf(os.Stderr, "No command\n")
+		os.Exit(2)
+	}
+
+	cmd, args := args[0], args[1:]
+	switch cmd {
+	case "console":
+		os.Exit((&ConsoleCommand{Meta: commandMeta()}).Run(args))
+	default:
+		fmt.Fprintf(os.Stderr, "Unknown command %q\n", cmd)
+		os.Exit(2)
+	}
+}
+
+func commandMeta() Meta {
+	basicUi := &packer.BasicUi{
+		Reader:      os.Stdin,
+		Writer:      os.Stdout,
+		ErrorWriter: os.Stdout,
+	}
+
+	CommandMeta := Meta{
+		CoreConfig: &packer.CoreConfig{
+			Components: getBareComponentFinder(),
+			Version:    version.Version,
+		},
+		Ui: basicUi,
+	}
+	return CommandMeta
+}
+
+func getBareComponentFinder() packer.ComponentFinder {
+	return packer.ComponentFinder{
+		BuilderStore: packer.MapOfBuilder{
+			"file": func() (packer.Builder, error) { return &file.Builder{}, nil },
+			"null": func() (packer.Builder, error) { return &null.Builder{}, nil },
+		},
+		ProvisionerStore: packer.MapOfProvisioner{
+			"shell-local": func() (packer.Provisioner, error) { return &shell_local.Provisioner{}, nil },
+			"shell":       func() (packer.Provisioner, error) { return &shell.Provisioner{}, nil },
+			"file":        func() (packer.Provisioner, error) { return &filep.Provisioner{}, nil },
+		},
+		PostProcessorStore: packer.MapOfPostProcessor{
+			"shell-local": func() (packer.PostProcessor, error) { return &shell_local_pp.PostProcessor{}, nil },
+			"manifest":    func() (packer.PostProcessor, error) { return &manifest.PostProcessor{}, nil },
+		},
+	}
+}

command/test-fixtures/var-arg/map.pkr.hcl

@@ -0,0 +1,7 @@
+
+variable "images" {
+  type    = map(string)
+  default = {
+    key = "value"
+  }
+}

hcl2template/parser.go

@@ -66,7 +66,7 @@ func (p *Parser) Parse(filename string, varFiles []string, argVars map[string]st
 	var diags hcl.Diagnostics
 
 	// parse config files
-	{
+	if filename != "" {
 		hclFiles, jsonFiles, moreDiags := GetHCL2Files(filename, hcl2FileExt, hcl2JsonFileExt)
 		diags = append(diags, moreDiags...)
 		if len(hclFiles)+len(jsonFiles) == 0 {

hcl2template/repl/format.go

@@ -0,0 +1,106 @@
+package repl
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// FormatResult formats the given result value for human-readable output.
+//
+// The value must currently be a string, list, map, and any nested values
+// with those same types.
+func FormatResult(value interface{}) string {
+	return formatResult(value, false)
+}
+
+func formatResult(value interface{}, nested bool) string {
+	if value == nil {
+		return "null"
+	}
+	switch output := value.(type) {
+	case string:
+		if nested {
+			return fmt.Sprintf("%q", output)
+		}
+		return output
+	case int:
+		return strconv.Itoa(output)
+	case float64:
+		return fmt.Sprintf("%g", output)
+	case bool:
+		switch {
+		case output == true:
+			return "true"
+		default:
+			return "false"
+		}
+	case []interface{}:
+		return formatListResult(output)
+	case map[string]interface{}:
+		return formatMapResult(output)
+	default:
+		return "<unknown-type>"
+	}
+}
+
+func formatListResult(value []interface{}) string {
+	var outputBuf bytes.Buffer
+	outputBuf.WriteString("[")
+	if len(value) > 0 {
+		outputBuf.WriteString("\n")
+	}
+
+	for _, v := range value {
+		raw := formatResult(v, true)
+		outputBuf.WriteString(indent(raw))
+		outputBuf.WriteString(",\n")
+	}
+
+	outputBuf.WriteString("]")
+	return outputBuf.String()
+}
+
+func formatMapResult(value map[string]interface{}) string {
+	ks := make([]string, 0, len(value))
+	for k := range value {
+		ks = append(ks, k)
+	}
+	sort.Strings(ks)
+
+	var outputBuf bytes.Buffer
+	outputBuf.WriteString("{")
+	if len(value) > 0 {
+		outputBuf.WriteString("\n")
+	}
+
+	for _, k := range ks {
+		v := value[k]
+		rawK := formatResult(k, true)
+		rawV := formatResult(v, true)
+
+		outputBuf.WriteString(indent(fmt.Sprintf("%s = %s", rawK, rawV)))
+		outputBuf.WriteString("\n")
+	}
+
+	outputBuf.WriteString("}")
+	return outputBuf.String()
+}
+
+func indent(value string) string {
+	var outputBuf bytes.Buffer
+	s := bufio.NewScanner(strings.NewReader(value))
+	newline := false
+	for s.Scan() {
+		if newline {
+			outputBuf.WriteByte('\n')
+		}
+		outputBuf.WriteString("  " + s.Text())
+		newline = true
+	}
+
+	return outputBuf.String()
+}

hcl2template/repl/repl.go

@@ -0,0 +1,4 @@
+// Package repl provides the structs and functions necessary to run REPL for
+// HCL2. The REPL allows experimentation of HCL2 interpolations without having
+// to run a HCL2 configuration.
+package repl

hcl2template/shim/values.go

@@ -0,0 +1,87 @@
+package hcl2shim
+
+import (
+	"fmt"
+	"math/big"
+
+	"github.com/zclconf/go-cty/cty"
+)
+
+// UnknownVariableValue is a sentinel value that can be used
+// to denote that the value of a variable is unknown at this time.
+// RawConfig uses this information to build up data about
+// unknown keys.
+const UnknownVariableValue = "74D93920-ED26-11E3-AC10-0800200C9A66"
+
+// ConfigValueFromHCL2 converts a value from HCL2 (really, from the cty dynamic
+// types library that HCL2 uses) to a value type that matches what would've
+// been produced from the HCL-based interpolator for an equivalent structure.
+//
+// This function will transform a cty null value into a Go nil value, which
+// isn't a possible outcome of the HCL/HIL-based decoder and so callers may
+// need to detect and reject any null values.
+func ConfigValueFromHCL2(v cty.Value) interface{} {
+	if !v.IsKnown() {
+		return UnknownVariableValue
+	}
+	if v.IsNull() {
+		return nil
+	}
+
+	switch v.Type() {
+	case cty.Bool:
+		return v.True() // like HCL.BOOL
+	case cty.String:
+		return v.AsString() // like HCL token.STRING or token.HEREDOC
+	case cty.Number:
+		// We can't match HCL _exactly_ here because it distinguishes between
+		// int and float values, but we'll get as close as we can by using
+		// an int if the number is exactly representable, and a float if not.
+		// The conversion to float will force precision to that of a float64,
+		// which is potentially losing information from the specific number
+		// given, but no worse than what HCL would've done in its own conversion
+		// to float.
+
+		f := v.AsBigFloat()
+		if i, acc := f.Int64(); acc == big.Exact {
+			// if we're on a 32-bit system and the number is too big for 32-bit
+			// int then we'll fall through here and use a float64.
+			const MaxInt = int(^uint(0) >> 1)
+			const MinInt = -MaxInt - 1
+			if i <= int64(MaxInt) && i >= int64(MinInt) {
+				return int(i) // Like HCL token.NUMBER
+			}
+		}
+
+		f64, _ := f.Float64()
+		return f64 // like HCL token.FLOAT
+	}
+
+	if v.Type().IsListType() || v.Type().IsSetType() || v.Type().IsTupleType() {
+		l := make([]interface{}, 0, v.LengthInt())
+		it := v.ElementIterator()
+		for it.Next() {
+			_, ev := it.Element()
+			l = append(l, ConfigValueFromHCL2(ev))
+		}
+		return l
+	}
+
+	if v.Type().IsMapType() || v.Type().IsObjectType() {
+		l := make(map[string]interface{})
+		it := v.ElementIterator()
+		for it.Next() {
+			ek, ev := it.Element()
+			cv := ConfigValueFromHCL2(ev)
+			if cv != nil {
+				l[ek.AsString()] = cv
+			}
+		}
+		return l
+	}
+
+	// If we fall out here then we have some weird type that we haven't
+	// accounted for. This should never happen unless the caller is using
+	// capsule types, and we don't currently have any such types defined.
+	panic(fmt.Errorf("can't convert %#v to config value", v))
+}

hcl2template/shim/values_test.go

@@ -0,0 +1,96 @@
+package hcl2shim
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"github.com/zclconf/go-cty/cty"
+)
+
+func TestConfigValueFromHCL2(t *testing.T) {
+	tests := []struct {
+		Input cty.Value
+		Want  interface{}
+	}{
+		{
+			cty.True,
+			true,
+		},
+		{
+			cty.False,
+			false,
+		},
+		{
+			cty.NumberIntVal(12),
+			int(12),
+		},
+		{
+			cty.NumberFloatVal(12.5),
+			float64(12.5),
+		},
+		{
+			cty.StringVal("hello world"),
+			"hello world",
+		},
+		{
+			cty.ObjectVal(map[string]cty.Value{
+				"name": cty.StringVal("Ermintrude"),
+				"age":  cty.NumberIntVal(19),
+				"address": cty.ObjectVal(map[string]cty.Value{
+					"street": cty.ListVal([]cty.Value{cty.StringVal("421 Shoreham Loop")}),
+					"city":   cty.StringVal("Fridgewater"),
+					"state":  cty.StringVal("MA"),
+					"zip":    cty.StringVal("91037"),
+				}),
+			}),
+			map[string]interface{}{
+				"name": "Ermintrude",
+				"age":  int(19),
+				"address": map[string]interface{}{
+					"street": []interface{}{"421 Shoreham Loop"},
+					"city":   "Fridgewater",
+					"state":  "MA",
+					"zip":    "91037",
+				},
+			},
+		},
+		{
+			cty.MapVal(map[string]cty.Value{
+				"foo": cty.StringVal("bar"),
+				"bar": cty.StringVal("baz"),
+			}),
+			map[string]interface{}{
+				"foo": "bar",
+				"bar": "baz",
+			},
+		},
+		{
+			cty.TupleVal([]cty.Value{
+				cty.StringVal("foo"),
+				cty.True,
+			}),
+			[]interface{}{
+				"foo",
+				true,
+			},
+		},
+		{
+			cty.NullVal(cty.String),
+			nil,
+		},
+		{
+			cty.UnknownVal(cty.String),
+			UnknownVariableValue,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("%#v", test.Input), func(t *testing.T) {
+			got := ConfigValueFromHCL2(test.Input)
+			if !reflect.DeepEqual(got, test.Want) {
+				t.Errorf("wrong result\ninput: %#v\ngot:   %#v\nwant:  %#v", test.Input, got, test.Want)
+			}
+		})
+	}
+}

hcl2template/types.packer_config.go

@@ -2,8 +2,10 @@ package hcl2template
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hclsyntax"
 	"github.com/hashicorp/packer/helper/common"
 	"github.com/hashicorp/packer/packer"
 	"github.com/zclconf/go-cty/cty"
@@ -12,8 +14,6 @@ import (
 // PackerConfig represents a loaded Packer HCL config. It will contain
 // references to all possible blocks of the allowed configuration.
 type PackerConfig struct {
-	// parser *Parser
-
 	// Directory where the config files are defined
 	Basedir string
 
@@ -386,3 +386,67 @@ func (cfg *PackerConfig) GetBuilds(opts packer.GetBuildsOptions) ([]packer.Build
 	}
 	return res, diags
 }
+
+var PackerConsoleHelp = strings.TrimSpace(`
+Packer console HCL2 Mode.
+The Packer console allows you to experiment with Packer interpolations.
+You may access variables and functions in the Packer config you called the
+console with.
+
+Type in the interpolation to test and hit <enter> to see the result.
+
+"upper(var.foo.id)" would evaluate to the ID of "foo" and uppercase is, if it
+exists in your config file.
+
+"variables" will dump all available variables and their values.
+
+To exit the console, type "exit" and hit <enter>, or use Control-C.
+
+/!\ It is not possible to use go templating interpolation like "{{timestamp}}"
+with in HCL2 mode.
+`)
+
+func (p *PackerConfig) EvaluateExpression(line string) (out string, exit bool, diags hcl.Diagnostics) {
+	switch {
+	case line == "":
+		return "", false, nil
+	case line == "exit":
+		return "", true, nil
+	case line == "help":
+		return PackerConsoleHelp, false, nil
+	case line == "variables":
+		out := &strings.Builder{}
+		out.WriteString("> input-variables:\n\n")
+		for _, v := range p.InputVariables {
+			val, _ := v.Value()
+			fmt.Fprintf(out, "var.%s: %q [debug: %#v]\n", v.Name, PrintableCtyValue(val), v)
+		}
+		out.WriteString("\n> local-variables:\n\n")
+		for _, v := range p.LocalVariables {
+			val, _ := v.Value()
+			fmt.Fprintf(out, "local.%s: %q\n", v.Name, PrintableCtyValue(val))
+		}
+
+		return out.String(), false, nil
+	default:
+		return p.handleEval(line)
+	}
+}
+
+func (p *PackerConfig) handleEval(line string) (out string, exit bool, diags hcl.Diagnostics) {
+
+	// Parse the given line as an expression
+	expr, parseDiags := hclsyntax.ParseExpression([]byte(line), "<console-input>", hcl.Pos{Line: 1, Column: 1})
+	diags = append(diags, parseDiags...)
+	if parseDiags.HasErrors() {
+		return "", false, diags
+	}
+
+	val, valueDiags := expr.Value(p.EvalContext(nil))
+	diags = append(diags, valueDiags...)
+	if valueDiags.HasErrors() {
+		return "", false, diags
+	}
+
+	return PrintableCtyValue(val), false, diags
+}

hcl2template/types.variables.go

@@ -51,8 +51,13 @@ type Variable struct {
 }
 
 func (v *Variable) GoString() string {
-	return fmt.Sprintf("{Type:%q,CmdValue:%q,VarfileValue:%q,EnvValue:%q,DefaultValue:%q}",
+	return fmt.Sprintf("{Type:%s,CmdValue:%s,VarfileValue:%s,EnvValue:%s,DefaultValue:%s}",
-		v.Type.GoString(), v.CmdValue.GoString(), v.VarfileValue.GoString(), v.EnvValue.GoString(), v.DefaultValue.GoString())
+		v.Type.GoString(),
+		PrintableCtyValue(v.CmdValue),
+		PrintableCtyValue(v.VarfileValue),
+		PrintableCtyValue(v.EnvValue),
+		PrintableCtyValue(v.DefaultValue),
+	)
 }
 
 func (v *Variable) Value() (cty.Value, *hcl.Diagnostic) {

hcl2template/utils.go

@@ -9,6 +9,9 @@ import (
 
 	"github.com/gobwas/glob"
 	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/packer/hcl2template/repl"
+	hcl2shim "github.com/hashicorp/packer/hcl2template/shim"
+	"github.com/zclconf/go-cty/cty"
 )
 
 func warningErrorsToDiags(block *hcl.Block, warnings []string, err error) hcl.Diagnostics {
@@ -47,6 +50,9 @@ func isDir(name string) (bool, error) {
 // returned. Otherwise if filename references a file and filename matches one
 // of the suffixes it is returned in the according slice.
 func GetHCL2Files(filename, hclSuffix, jsonSuffix string) (hclFiles, jsonFiles []string, diags hcl.Diagnostics) {
+	if filename == "" {
+		return
+	}
 	isDir, err := isDir(filename)
 	if err != nil {
 		diags = append(diags, &hcl.Diagnostic{
@@ -109,3 +115,12 @@ func convertFilterOption(patterns []string, optionName string) ([]glob.Glob, hcl
 
 	return globs, diags
 }
+
+func PrintableCtyValue(v cty.Value) string {
+	if !v.IsWhollyKnown() {
+		return "<unknown>"
+	}
+	gval := hcl2shim.ConfigValueFromHCL2(v)
+	str := repl.FormatResult(gval)
+	return str
+}

packer/core.go

@@ -374,6 +374,52 @@ func (c *Core) Context() *interpolate.Context {
 	}
 }
 
+var ConsoleHelp = strings.TrimSpace(`
+Packer console JSON Mode.
+The Packer console allows you to experiment with Packer interpolations.
+You may access variables in the Packer config you called the console with.
+
+Type in the interpolation to test and hit <enter> to see the result.
+
+"variables" will dump all available variables and their values.
+
+"{{timestamp}}" will output the timestamp, for example "1559855090".
+
+To exit the console, type "exit" and hit <enter>, or use Control-C.
+
+/!\ If you would like to start console in hcl2 mode without a config you can
+use the --config-type=hcl2 option.
+`)
+
+func (c *Core) EvaluateExpression(line string) (string, bool, hcl.Diagnostics) {
+	switch {
+	case line == "":
+		return "", false, nil
+	case line == "exit":
+		return "", true, nil
+	case line == "help":
+		return ConsoleHelp, false, nil
+	case line == "variables":
+		varsstring := "\n"
+		for k, v := range c.Context().UserVariables {
+			varsstring += fmt.Sprintf("%s: %+v,\n", k, v)
+		}
+
+		return varsstring, false, nil
+	default:
+		ctx := c.Context()
+		rendered, err := interpolate.Render(line, ctx)
+		var diags hcl.Diagnostics
+		if err != nil {
+			diags = append(diags, &hcl.Diagnostic{
+				Summary: "Interpolation error",
+				Detail:  err.Error(),
+			})
+		}
+		return rendered, false, diags
+	}
+}
+
 // validate does a full validation of the template.
 //
 // This will automatically call template.validate() in addition to doing

packer/run_interfaces.go

@@ -17,6 +17,19 @@ type BuildGetter interface {
 	GetBuilds(GetBuildsOptions) ([]Build, hcl.Diagnostics)
 }
 
+type Evaluator interface {
+	// EvaluateExpression is meant to be used in the `packer console` command.
+	// It parses the input string and returns what needs to be displayed. In
+	// case of an error the error should be displayed.
+	EvaluateExpression(expr string) (output string, exit bool, diags hcl.Diagnostics)
+}
+
+// The packer.Handler handles all Packer things.
+type Handler interface {
+	Evaluator
+	BuildGetter
+}
+
 //go:generate enumer -type FixConfigMode
 type FixConfigMode int
 

website/pages/docs/commands/console.mdx

@@ -16,9 +16,13 @@ console with, or provide variables when you call console using the -var or
 
 ~> **Note:** `console` is available from version 1.4.2 and above.
 
-Type in the interpolation to test and hit \<enter\> to see the result.
+~> **Note:** For HCL2 `console` is available from version 1.6.0 and above, use
+`packer console --config-type=hcl2` to try it without a config file. Go
+templating ( or `{{..}}` calls ) will not work in HCL2 mode.
 
-To exit the console, type "exit" and hit \<enter\>, or use Control-C.
+Type in the interpolation to test and hit `<enter>` to see the result.
+
+To exit the console, type "exit" and hit `<enter>`, or use Control-C.
 
 ```shell-session
 $ packer console my_template.json
@@ -45,7 +49,7 @@ help output, which can be seen via `packer console -h`.
 - `variables` - prints a list of all variables read into the console from the
   `-var` option, `-var-files` option, and template.
 
-## Usage Examples
+## Usage Examples - repl session ( JSON )
 
 Let's say you launch a console using a Packer template `example_template.json`:
 
@@ -69,14 +73,14 @@ myvar:
 
 ```shell-session
 > {{user `myvar`}}
-> asdfasdf
+asdfasdf
 ```
 
 From there you can test more complicated interpolations:
 
 ```shell-session
 > {{user `myvar`}}-{{timestamp}}
-> asdfasdf-1559854396
+asdfasdf-1559854396
 ```
 
 And when you're done using the console, just type "exit" or CTRL-C
@@ -96,6 +100,8 @@ If you don't have specific variables or var files you want to test, and just
 want to experiment with a particular template engine, you can do so by simply
 calling `packer console` without a template file.
 
+## Usage Examples - piped commands ( JSON )
+
 If you'd like to just see a specific single interpolation without launching
 the REPL, you can do so by echoing and piping the string into the console
 command:
@@ -104,3 +110,49 @@ command:
 $ echo {{timestamp}} | packer console
 1559855090
 ```
+
+## Usage Examples - repl session ( HCL2 )
+
+~> **Note:** For HCL2 `console` is available from version 1.6.0 and above, use
+`packer console --config-type=hcl2` to try it without a config file. Go
+templating ( or `{{..}}` calls ) will not work in HCL2 mode.
+
+Without a config file, `packer console` can be used to experiment with the
+expression syntax and [built-in functions](/docs/from-1.5/functions).
+
+### Starting
+
+To start a session on a folder containing HCL2 config files, run:
+
+```shell-session
+packer console folder/
+```
+
+Because `folder/` is a folder Packer will start in HCL2 mode, you can also
+directly pass an HCL2 formatted config file: 
+
+```shell-session
+packer console file.pkr.hcl
+```
+
+Because the file is suffixed with `.pkr.hcl` Packer will start in HCL2 mode.
+
+When you just want to play arround without a config file you can set the
+`--config-type=hcl2` option and Packer will start in HCL2 mode:
+
+```shell-session
+packer console --config-type=hcl2
+```
+
+### Scripting
+
+The `packer console` command can be used in non-interactive scripts by piping
+newline-separated commands to it. Only the output from the final command is
+printed unless an error occurs earlier.
+
+For example:
+
+```shell-session
+$ echo "1 + 5" | terraform console
+6
+```