github.com/hashicorp/packer@v1.14.3/packer/core.go

// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: BUSL-1.1

package packer

import (
	"encoding/json"
	"fmt"
	"log"
	"regexp"
	"sort"
	"strconv"
	"strings"

	ttmp "text/template"

	"github.com/google/go-cmp/cmp"
	multierror "github.com/hashicorp/go-multierror"
	version "github.com/hashicorp/go-version"
	hcl "github.com/hashicorp/hcl/v2"
	"github.com/hashicorp/packer-plugin-sdk/didyoumean"
	packersdk "github.com/hashicorp/packer-plugin-sdk/packer"
	"github.com/hashicorp/packer-plugin-sdk/template"
	"github.com/hashicorp/packer-plugin-sdk/template/interpolate"
	plugingetter "github.com/hashicorp/packer/packer/plugin-getter"
	packerversion "github.com/hashicorp/packer/version"
)

// Core is the main executor of Packer. If Packer is being used as a
// library, this is the struct you'll want to instantiate to get anything done.
type Core struct {
	Template *template.Template

	components ComponentFinder
	variables  map[string]string
	builds     map[string]*template.Builder
	version    string
	secrets    []string

	except []string
	only   []string
}

// CoreConfig is the structure for initializing a new Core. Once a CoreConfig
// is used to initialize a Core, it shouldn't be re-used or modified again.
type CoreConfig struct {
	Components         ComponentFinder
	Template           *template.Template
	Variables          map[string]string
	SensitiveVariables []string
	Version            string

	// These are set by command-line flags
	Except []string
	Only   []string
}

// The function type used to lookup Builder implementations.
type BuilderFunc func(name string) (packersdk.Builder, error)

// The function type used to lookup Hook implementations.
type HookFunc func(name string) (packersdk.Hook, error)

// The function type used to lookup PostProcessor implementations.
type PostProcessorFunc func(name string) (packersdk.PostProcessor, error)

// The function type used to lookup Provisioner implementations.
type ProvisionerFunc func(name string) (packersdk.Provisioner, error)

type BasicStore interface {
	Has(name string) bool
	List() (names []string)
}

type BuilderStore interface {
	BasicStore
	Start(name string) (packersdk.Builder, error)
}

type BuilderSet interface {
	BuilderStore
	Set(name string, starter func() (packersdk.Builder, error))
}

type ProvisionerStore interface {
	BasicStore
	Start(name string) (packersdk.Provisioner, error)
}

type ProvisionerSet interface {
	ProvisionerStore
	Set(name string, starter func() (packersdk.Provisioner, error))
}

type PostProcessorStore interface {
	BasicStore
	Start(name string) (packersdk.PostProcessor, error)
}

type PostProcessorSet interface {
	PostProcessorStore
	Set(name string, starter func() (packersdk.PostProcessor, error))
}

type DatasourceStore interface {
	BasicStore
	Start(name string) (packersdk.Datasource, error)
}

type DatasourceSet interface {
	DatasourceStore
	Set(name string, starter func() (packersdk.Datasource, error))
}

// ComponentFinder is a struct that contains the various function
// pointers necessary to look up components of Packer such as builders,
// commands, etc.
type ComponentFinder struct {
	Hook         HookFunc
	PluginConfig *PluginConfig
}

// NewCore creates a new Core.
func NewCore(c *CoreConfig) *Core {
	core := &Core{
		Template:   c.Template,
		components: c.Components,
		variables:  c.Variables,
		version:    c.Version,
		only:       c.Only,
		except:     c.Except,
	}
	return core
}

// DetectPluginBinaries is used to load required plugins from the template,
// since it is unsupported in JSON, this is essentially a no-op.
func (c *Core) DetectPluginBinaries() hcl.Diagnostics {
	var diags hcl.Diagnostics

	err := c.components.PluginConfig.Discover()
	if err != nil {
		diags = diags.Append(&hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Failed to discover installed plugins",
			Detail:   err.Error(),
		})
	}

	return diags
}

func (c *Core) Initialize(_ InitializeOptions) hcl.Diagnostics {
	err := c.initialize()
	if err != nil {
		return hcl.Diagnostics{
			&hcl.Diagnostic{
				Detail:   err.Error(),
				Severity: hcl.DiagError,
			},
		}
	}
	return nil
}

func (core *Core) initialize() error {
	if err := core.validate(); err != nil {
		return err
	}
	if err := core.init(); err != nil {
		return err
	}
	for _, secret := range core.secrets {
		packersdk.LogSecretFilter.Set(secret)
	}

	// Go through and interpolate all the build names. We should be able
	// to do this at this point with the variables.
	core.builds = make(map[string]*template.Builder)
	for _, b := range core.Template.Builders {
		v, err := interpolate.Render(b.Name, core.Context())
		if err != nil {
			return fmt.Errorf(
				"Error interpolating builder '%s': %s",
				b.Name, err)
		}

		core.builds[v] = b
	}

	return nil
}

func (c *Core) PluginRequirements() (plugingetter.Requirements, hcl.Diagnostics) {
	return nil, hcl.Diagnostics{
		&hcl.Diagnostic{
			Summary:  "Packer plugins currently only works with HCL2 configuration templates",
			Detail:   "Please manually install plugins with the plugins command or use a HCL2 configuration that will do that for you.",
			Severity: hcl.DiagError,
		},
	}
}

// BuildNames returns the builds that are available in this configured core.
func (c *Core) BuildNames(only, except []string) []string {

	sort.Strings(only)
	sort.Strings(except)
	c.except = except
	c.only = only

	r := make([]string, 0, len(c.builds))
	for n := range c.builds {
		onlyPos := sort.SearchStrings(only, n)
		foundInOnly := onlyPos < len(only) && only[onlyPos] == n
		if len(only) > 0 && !foundInOnly {
			continue
		}

		if pos := sort.SearchStrings(except, n); pos < len(except) && except[pos] == n {
			continue
		}
		r = append(r, n)
	}
	sort.Strings(r)

	return r
}

func (c *Core) generateCoreBuildProvisioner(rawP *template.Provisioner, rawName string) (CoreBuildProvisioner, error) {
	// Get the provisioner
	cbp := CoreBuildProvisioner{}

	if !c.components.PluginConfig.Provisioners.Has(rawP.Type) {
		err := fmt.Errorf(
			"The provisioner %s is unknown by Packer, and is likely part of a plugin that is not installed.\n"+
				"You may find the needed plugin along with installation instructions documented on the Packer integrations page.\n\n"+
				"https://developer.hashicorp.com/packer/integrations?filter=%s",
			rawP.Type,
			strings.Split(rawP.Type, "-")[0],
		)

		if sugg := didyoumean.NameSuggestion(rawP.Type, c.components.PluginConfig.Provisioners.List()); sugg != "" {
			err = fmt.Errorf("Did you mean to use %q?", sugg)
		}

		return cbp, err
	}

	provisioner, err := c.components.PluginConfig.Provisioners.Start(rawP.Type)
	if err != nil {
		return cbp, fmt.Errorf(
			"error initializing provisioner '%s': %s",
			rawP.Type, err)
	}
	// Seems unlikely that a provisioner doesn't start successfully without error
	if provisioner == nil {
		return cbp, fmt.Errorf(
			"provisioner failed to be started and did not error: %s", rawP.Type)
	}

	// Get the configuration
	config := make([]interface{}, 1, 2)
	config[0] = rawP.Config
	if rawP.Override != nil {
		if override, ok := rawP.Override[rawName]; ok {
			config = append(config, override)
		}
	}
	// If we're pausing, we wrap the provisioner in a special pauser.
	if rawP.PauseBefore != 0 {
		provisioner = &PausedProvisioner{
			PauseBefore: rawP.PauseBefore,
			Provisioner: provisioner,
		}
	} else if rawP.Timeout != 0 {
		provisioner = &TimeoutProvisioner{
			Timeout:     rawP.Timeout,
			Provisioner: provisioner,
		}
	}
	maxRetries := 0
	if rawP.MaxRetries != "" {
		renderedMaxRetries, err := interpolate.Render(rawP.MaxRetries, c.Context())
		if err != nil {
			return cbp, fmt.Errorf("failed to interpolate `max_retries`: %s", err.Error())
		}
		maxRetries, err = strconv.Atoi(renderedMaxRetries)
		if err != nil {
			return cbp, fmt.Errorf("`max_retries` must be a valid integer: %s", err.Error())
		}
	}
	if maxRetries != 0 {
		provisioner = &RetriedProvisioner{
			MaxRetries:  maxRetries,
			Provisioner: provisioner,
		}
	}

	if rawP.Type == "hcp-sbom" {
		provisioner = &SBOMInternalProvisioner{
			Provisioner: provisioner,
		}
	}

	cbp = CoreBuildProvisioner{
		PType:       rawP.Type,
		Provisioner: provisioner,
		config:      config,
	}

	return cbp, nil
}

// This is used for json templates to launch the build plugins.
// They will be prepared via b.Prepare() later.
func (c *Core) GetBuilds(opts GetBuildsOptions) ([]*CoreBuild, hcl.Diagnostics) {
	buildNames := c.BuildNames(opts.Only, opts.Except)
	builds := []*CoreBuild{}
	diags := hcl.Diagnostics{}
	for _, n := range buildNames {
		b, err := c.Build(n)
		if err != nil {
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  fmt.Sprintf("Failed to initialize build %q", n),
				Detail:   err.Error(),
			})
			continue
		}

		// Now that build plugin has been launched, call Prepare()
		log.Printf("Preparing build: %s", b.Name())
		b.SetDebug(opts.Debug)
		b.SetForce(opts.Force)
		b.SetOnError(opts.OnError)

		warnings, err := b.Prepare()
		if err != nil {
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  fmt.Sprintf("Failed to prepare build: %q", n),
				Detail:   err.Error(),
			})
			continue
		}

		// Only append builds to list if the Prepare() is successful.
		builds = append(builds, b)

		if len(warnings) > 0 {
			for _, warning := range warnings {
				diags = append(diags, &hcl.Diagnostic{
					Severity: hcl.DiagWarning,
					Summary:  fmt.Sprintf("Warning when preparing build: %q", n),
					Detail:   warning,
				})
			}
		}
	}
	return builds, diags
}

// Build returns the Build object for the given name.
func (c *Core) Build(n string) (*CoreBuild, error) {
	// Setup the builder
	configBuilder, ok := c.builds[n]
	if !ok {
		return nil, fmt.Errorf("no such build found: %s", n)
	}
	// BuilderStore = config.Builders, gathered in loadConfig() in main.go
	// For reference, the builtin BuilderStore is generated in
	// packer/config.go in the Discover() func.

	if !c.components.PluginConfig.Builders.Has(configBuilder.Type) {
		err := fmt.Errorf(
			"The builder %s is unknown by Packer, and is likely part of a plugin that is not installed.\n"+
				"You may find the needed plugin along with installation instructions documented on the Packer integrations page.\n\n"+
				"https://developer.hashicorp.com/packer/integrations?filter=%s",
			configBuilder.Type,
			strings.Split(configBuilder.Type, "-")[0],
		)

		if sugg := didyoumean.NameSuggestion(configBuilder.Type, c.components.PluginConfig.Builders.List()); sugg != "" {
			err = fmt.Errorf("Did you mean to use %q?", sugg)
		}

		return nil, err
	}

	// the Start command launches the builder plugin of the given type without
	// calling Prepare() or passing any build-specific details.
	builder, err := c.components.PluginConfig.Builders.Start(configBuilder.Type)
	if err != nil {
		return nil, fmt.Errorf(
			"error initializing builder '%s': %s",
			configBuilder.Type, err)
	}
	if builder == nil {
		return nil, fmt.Errorf(
			"builder type not found: %s", configBuilder.Type)
	}

	// rawName is the uninterpolated name that we use for various lookups
	rawName := configBuilder.Name

	// Setup the provisioners for this build
	provisioners := make([]CoreBuildProvisioner, 0, len(c.Template.Provisioners))
	for _, rawP := range c.Template.Provisioners {
		// If we're skipping this, then ignore it
		if rawP.OnlyExcept.Skip(rawName) {
			continue
		}
		cbp, err := c.generateCoreBuildProvisioner(rawP, rawName)
		if err != nil {
			return nil, err
		}

		provisioners = append(provisioners, cbp)
	}

	var cleanupProvisioner CoreBuildProvisioner
	if c.Template.CleanupProvisioner != nil {
		// This is a special instantiation of the shell-local provisioner that
		// is only run on error at end of provisioning step before other step
		// cleanup occurs.
		cleanupProvisioner, err = c.generateCoreBuildProvisioner(c.Template.CleanupProvisioner, rawName)
		if err != nil {
			return nil, err
		}
	}

	// Setup the post-processors
	postProcessors := make([][]CoreBuildPostProcessor, 0, len(c.Template.PostProcessors))
	for _, rawPs := range c.Template.PostProcessors {
		current := make([]CoreBuildPostProcessor, 0, len(rawPs))
		for _, rawP := range rawPs {
			if rawP.Skip(rawName) {
				continue
			}
			// -except skips post-processor & build
			foundExcept := false
			for _, except := range c.except {
				if except != "" && except == rawP.Name {
					foundExcept = true
				}
			}
			if foundExcept {
				break
			}

			if !c.components.PluginConfig.PostProcessors.Has(rawP.Type) {
				err := fmt.Errorf(
					"The post-processor %s is unknown by Packer, and is likely part of a plugin that is not installed.\n"+
						"You may find the needed plugin along with installation instructions documented on the Packer integrations page.\n\n"+
						"https://developer.hashicorp.com/packer/integrations?filter=%s",
					rawP.Type,
					strings.Split(rawP.Type, "-")[0],
				)

				if sugg := didyoumean.NameSuggestion(rawP.Type, c.components.PluginConfig.PostProcessors.List()); sugg != "" {
					err = fmt.Errorf("Did you mean to use %q?", sugg)
				}

				return nil, err
			}

			// Get the post-processor
			postProcessor, err := c.components.PluginConfig.PostProcessors.Start(rawP.Type)
			if err != nil {
				return nil, fmt.Errorf(
					"error initializing post-processor '%s': %s",
					rawP.Type, err)
			}
			if postProcessor == nil {
				return nil, fmt.Errorf(
					"post-processor type not found: %s", rawP.Type)
			}

			current = append(current, CoreBuildPostProcessor{
				PostProcessor:     postProcessor,
				PType:             rawP.Type,
				PName:             rawP.Name,
				config:            rawP.Config,
				KeepInputArtifact: rawP.KeepInputArtifact,
			})
		}

		// If we have no post-processors in this chain, just continue.
		if len(current) == 0 {
			continue
		}

		postProcessors = append(postProcessors, current)
	}

	var sensitiveVars []string
	for _, sensitive := range c.Template.SensitiveVariables {
		sensitiveVars = append(sensitiveVars, sensitive.Key)
	}

	// TODO hooks one day

	// Return a structure that contains the plugins, their types, variables, and
	// the raw builder config loaded from the json template
	cb := &CoreBuild{
		Type:               n,
		Builder:            builder,
		BuilderConfig:      configBuilder.Config,
		BuilderType:        configBuilder.Type,
		PostProcessors:     postProcessors,
		Provisioners:       provisioners,
		CleanupProvisioner: cleanupProvisioner,
		TemplatePath:       c.Template.Path,
		Variables:          c.variables,
		SensitiveVars:      sensitiveVars,
	}

	//configBuilder.Name is left uninterpolated so we must check against
	// the interpolated name.
	if configBuilder.Type != configBuilder.Name {
		cb.BuildName = configBuilder.Type
	}

	return cb, nil
}

// Context returns an interpolation context.
func (c *Core) Context() *interpolate.Context {
	return &interpolate.Context{
		TemplatePath:            c.Template.Path,
		UserVariables:           c.variables,
		CorePackerVersionString: packerversion.FormattedVersion(),
	}
}

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
	}
}

func (c *Core) InspectConfig(opts InspectConfigOptions) int {

	// Convenience...
	ui := opts.Ui
	tpl := c.Template
	ui.Say("Packer Inspect: JSON mode")

	// Description
	if tpl.Description != "" {
		ui.Say("Description:\n")
		ui.Say(tpl.Description + "\n")
	}

	// Variables
	if len(tpl.Variables) == 0 {
		ui.Say("Variables:\n")
		ui.Say("  <No variables>")
	} else {
		requiredHeader := false
		for k, v := range tpl.Variables {
			for _, sensitive := range tpl.SensitiveVariables {
				if ok := strings.Compare(sensitive.Default, v.Default); ok == 0 {
					v.Default = "<sensitive>"
				}
			}
			if v.Required {
				if !requiredHeader {
					requiredHeader = true
					ui.Say("Required variables:\n")
				}

				ui.Machine("template-variable", k, v.Default, "1")
				ui.Say("  " + k)
			}
		}

		if requiredHeader {
			ui.Say("")
		}

		ui.Say("Optional variables and their defaults:\n")
		keys := make([]string, 0, len(tpl.Variables))
		max := 0
		for k := range tpl.Variables {
			keys = append(keys, k)
			if len(k) > max {
				max = len(k)
			}
		}

		sort.Strings(keys)

		for _, k := range keys {
			v := tpl.Variables[k]
			if v.Required {
				continue
			}
			for _, sensitive := range tpl.SensitiveVariables {
				if ok := strings.Compare(sensitive.Default, v.Default); ok == 0 {
					v.Default = "<sensitive>"
				}
			}

			padding := strings.Repeat(" ", max-len(k))
			output := fmt.Sprintf("  %s%s = %s", k, padding, v.Default)

			ui.Machine("template-variable", k, v.Default, "0")
			ui.Say(output)
		}
	}

	ui.Say("")

	// Builders
	ui.Say("Builders:\n")
	if len(tpl.Builders) == 0 {
		ui.Say("  <No builders>")
	} else {
		keys := make([]string, 0, len(tpl.Builders))
		max := 0
		for k := range tpl.Builders {
			keys = append(keys, k)
			if len(k) > max {
				max = len(k)
			}
		}

		sort.Strings(keys)

		for _, k := range keys {
			v := tpl.Builders[k]
			padding := strings.Repeat(" ", max-len(k))
			output := fmt.Sprintf("  %s%s", k, padding)
			if v.Name != v.Type {
				output = fmt.Sprintf("%s (%s)", output, v.Type)
			}

			ui.Machine("template-builder", k, v.Type)
			ui.Say(output)

		}
	}

	ui.Say("")

	// Provisioners
	ui.Say("Provisioners:\n")
	if len(tpl.Provisioners) == 0 {
		ui.Say("  <No provisioners>")
	} else {
		for _, v := range tpl.Provisioners {
			ui.Machine("template-provisioner", v.Type)
			ui.Say(fmt.Sprintf("  %s", v.Type))
		}
	}

	ui.Say("\nNote: If your build names contain user variables or template\n" +
		"functions such as 'timestamp', these are processed at build time,\n" +
		"and therefore only show in their raw form here.")

	return 0
}

func (c *Core) FixConfig(opts FixConfigOptions) hcl.Diagnostics {
	var diags hcl.Diagnostics

	// Remove once we have support for the Inplace FixConfigMode
	if opts.Mode != Diff {
		diags = append(diags, &hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  fmt.Sprintf("FixConfig only supports template diff; FixConfigMode %d not supported", opts.Mode),
		})

		return diags
	}

	var rawTemplateData map[string]interface{}
	input := make(map[string]interface{})
	templateData := make(map[string]interface{})
	if err := json.Unmarshal(c.Template.RawContents, &rawTemplateData); err != nil {
		diags = append(diags, &hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  fmt.Sprintf("unable to read the contents of the JSON configuration file: %s", err),
			Detail:   err.Error(),
		})
		return diags
	}
	// Hold off on Diff for now - need to think about displaying to user.
	// delete empty top-level keys since the fixers seem to add them
	// willy-nilly
	for k := range input {
		ml, ok := input[k].([]map[string]interface{})
		if !ok {
			continue
		}
		if len(ml) == 0 {
			delete(input, k)
		}
	}
	// marshal/unmarshal to make comparable to templateData
	var fixedData map[string]interface{}
	// Guaranteed to be valid json, so we can ignore errors
	j, _ := json.Marshal(input)
	if err := json.Unmarshal(j, &fixedData); err != nil {
		diags = append(diags, &hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  fmt.Sprintf("unable to read the contents of the JSON configuration file: %s", err),
			Detail:   err.Error(),
		})

		return diags
	}

	if diff := cmp.Diff(templateData, fixedData); diff != "" {
		diags = append(diags, &hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Fixable configuration found.\nPlease run `packer fix` to get your build to run correctly.\nSee debug log for more information.",
			Detail:   diff,
		})
	}
	return diags
}

// validate does a full validation of the template.
//
// This will automatically call template.validate() in addition to doing
// richer semantic checks around variables and so on.
func (c *Core) validate() error {
	// First validate the template in general, we can't do anything else
	// unless the template itself is valid.
	if err := c.Template.Validate(); err != nil {
		return err
	}

	// Validate the minimum version is satisfied
	if c.Template.MinVersion != "" {
		versionActual, err := version.NewVersion(c.version)
		if err != nil {
			// This shouldn't happen since we set it via the compiler
			panic(err)
		}

		versionMin, err := version.NewVersion(c.Template.MinVersion)
		if err != nil {
			return fmt.Errorf(
				"min_version is invalid: %s", err)
		}

		if versionActual.LessThan(versionMin) {
			return fmt.Errorf(
				"This template requires Packer version %s or higher; using %s",
				versionMin,
				versionActual)
		}
	}

	// Validate variables are set
	var err error
	for n, v := range c.Template.Variables {
		if v.Required {
			if _, ok := c.variables[n]; !ok {
				err = multierror.Append(err, fmt.Errorf(
					"required variable not set: %s", n))
			}
		}
	}

	// TODO: validate all builders exist
	// TODO: ^^ provisioner
	// TODO: ^^ post-processor

	return err
}

func isDoneInterpolating(v string) (bool, error) {
	// Check for whether the var contains any more references to `user`, wrapped
	// in interpolation syntax.
	filter := `{{\s*user\s*\x60.*\x60\s*}}`
	matched, err := regexp.MatchString(filter, v)
	if err != nil {
		return false, fmt.Errorf("Can't tell if interpolation is done: %s", err)
	}
	if matched {
		// not done interpolating; there's still a call to "user" in a template
		// engine
		return false, nil
	}
	// No more calls to "user" as a template engine, so we're done.
	return true, nil
}

func (c *Core) renderVarsRecursively() (*interpolate.Context, error) {
	ctx := c.Context()
	ctx.EnableEnv = true
	ctx.UserVariables = make(map[string]string)
	shouldRetry := true
	changed := false
	failedInterpolation := ""

	// Why this giant loop?  User variables can be recursively defined. For
	// example:
	// "variables": {
	//    	"foo":  "bar",
	//	 	"baz":  "{{user `foo`}}baz",
	// 		"bang": "bang{{user `baz`}}"
	// },
	// In this situation, we cannot guarantee that we've added "foo" to
	// UserVariables before we try to interpolate "baz" the first time. We need
	// to have the option to loop back over in order to add the properly
	// interpolated "baz" to the UserVariables map.
	// Likewise, we'd need to loop up to two times to properly add "bang",
	// since that depends on "baz" being set, which depends on "foo" being set.

	// We break out of the while loop either if all our variables have been
	// interpolated or if after 100 loops we still haven't succeeded in
	// interpolating them.  Please don't actually nest your variables in 100
	// layers of other variables. Please.

	// c.Template.Variables is populated by variables defined within the Template
	// itself
	// c.variables is populated by variables read in from the command line and
	// var-files.
	// We need to read the keys from both, then loop over all of them to figure
	// out the appropriate interpolations.

	repeatMap := make(map[string]string)
	allKeys := make([]string, 0)

	// load in template variables
	for k, v := range c.Template.Variables {
		repeatMap[k] = v.Default
		allKeys = append(allKeys, k)
	}

	// overwrite template variables with command-line-read variables
	for k, v := range c.variables {
		repeatMap[k] = v
		allKeys = append(allKeys, k)
	}

	// sort map to force the following loop to be deterministic.
	sort.Strings(allKeys)
	type keyValue struct {
		Key   string
		Value string
	}
	sortedMap := make([]keyValue, 0, len(repeatMap))
	for _, k := range allKeys {
		sortedMap = append(sortedMap, keyValue{k, repeatMap[k]})
	}

	// Regex to exclude any build function variable or template variable
	// from interpolating earlier
	// E.g.: {{ .HTTPIP }}  won't interpolate now
	renderFilter := "{{(\\s|)\\.(.*?)(\\s|)}}"

	for i := 0; i < 100; i++ {
		shouldRetry = false
		changed = false
		deleteKeys := []string{}
		// First, loop over the variables in the template
		for _, kv := range sortedMap {
			// Interpolate the default
			renderedV, err := interpolate.RenderRegex(kv.Value, ctx, renderFilter)
			switch err := err.(type) {
			case nil:
				// We only get here if interpolation has succeeded, so something is
				// different in this loop than in the last one.
				changed = true
				c.variables[kv.Key] = renderedV
				ctx.UserVariables = c.variables
				// Remove fully-interpolated variables from the map, and flag
				// variables that still need interpolating for a repeat.
				done, err := isDoneInterpolating(kv.Value)
				if err != nil {
					return ctx, err
				}
				if done {
					deleteKeys = append(deleteKeys, kv.Key)
				} else {
					shouldRetry = true
				}
			case ttmp.ExecError:
				if strings.Contains(err.Error(), interpolate.ErrVariableNotSetString) {
					shouldRetry = true
					failedInterpolation = fmt.Sprintf(`"%s": "%s"; error: %s`, kv.Key, kv.Value, err)
				} else {
					return ctx, err
				}
			default:
				return ctx, fmt.Errorf(
					// unexpected interpolation error: abort the run
					"error interpolating default value for '%s': %s",
					kv.Key, err)
			}
		}
		if !shouldRetry {
			break
		}

		// Clear completed vars from sortedMap before next loop. Do this one
		// key at a time because the indices are gonna change ever time you
		// delete from the map.
		for _, k := range deleteKeys {
			for ind, kv := range sortedMap {
				if kv.Key == k {
					sortedMap = append(sortedMap[:ind], sortedMap[ind+1:]...)
					break
				}
			}
		}
	}

	if !changed && shouldRetry {
		return ctx, fmt.Errorf("Failed to interpolate %s: Please make sure that "+
			"the variable you're referencing has been defined; Packer treats "+
			"all variables used to interpolate other user variables as "+
			"required.", failedInterpolation)
	}

	return ctx, nil
}

func (c *Core) init() error {
	if c.variables == nil {
		c.variables = make(map[string]string)
	}
	// Go through the variables and interpolate the environment and
	// user variables
	ctx, err := c.renderVarsRecursively()
	if err != nil {
		return err
	}
	for _, v := range c.Template.SensitiveVariables {
		secret := ctx.UserVariables[v.Key]
		c.secrets = append(c.secrets, secret)
	}

	return nil
}