implement custom data type "trilean" (tri-state-boolean) to track booleans which have a "null" or "unset" state. Previously we used *bool for these template options, but it turns out that those won't work because "unset" will evaluate to "false" if a user is using template variables to set the option that maps to a *bool.

builder/alicloud/ecs/builder_test.go

@@ -4,6 +4,7 @@ import (
 	"reflect"
 	"testing"
 
+	helperconfig "github.com/hashicorp/packer/helper/config"
 	"github.com/hashicorp/packer/packer"
 )
 
@@ -126,13 +127,16 @@ func TestBuilderPrepare_Devices(t *testing.T) {
 	if err != nil {
 		t.Fatalf("should not have error: %s", err)
 	}
-	if !reflect.DeepEqual(b.config.ECSSystemDiskMapping, AlicloudDiskDevice{
+	expected := AlicloudDiskDevice{
 		DiskCategory: "cloud",
 		Description:  "system disk",
 		DiskName:     "system_disk",
 		DiskSize:     60,
-	}) {
+		RawEncrypted: helperconfig.TriUnset,
-		t.Fatalf("system disk is not set properly, actual: %#v", b.config.ECSSystemDiskMapping)
+		Encrypted:    nil,
+	}
+	if !reflect.DeepEqual(b.config.ECSSystemDiskMapping, expected) {
+		t.Fatalf("system disk is not set properly, actual: %v; expected: %v", b.config.ECSSystemDiskMapping, expected)
 	}
 	if !reflect.DeepEqual(b.config.ECSImagesDiskMappings, []AlicloudDiskDevice{
 		{

builder/alicloud/ecs/image_config.go

@@ -5,6 +5,7 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/hashicorp/packer/helper/config"
 	"github.com/hashicorp/packer/template/interpolate"
 )
 
@@ -16,7 +17,9 @@ type AlicloudDiskDevice struct {
 	Description        string         `mapstructure:"disk_description"`
 	DeleteWithInstance bool           `mapstructure:"disk_delete_with_instance"`
 	Device             string         `mapstructure:"disk_device"`
-	Encrypted          *bool  `mapstructure:"disk_encrypted"`
+	RawEncrypted       config.Trilean `mapstructure:"disk_encrypted"`
+
+	Encrypted *bool
 }
 
 type AlicloudDiskDevices struct {
@@ -32,7 +35,7 @@ type AlicloudImageConfig struct {
 	AlicloudImageUNShareAccounts      []string          `mapstructure:"image_unshare_account"`
 	AlicloudImageDestinationRegions   []string          `mapstructure:"image_copy_regions"`
 	AlicloudImageDestinationNames     []string          `mapstructure:"image_copy_names"`
-	ImageEncrypted                    *bool             `mapstructure:"image_encrypted"`
+	RawImageEncrypted                 config.Trilean    `mapstructure:"image_encrypted"`
 	AlicloudImageForceDelete          bool              `mapstructure:"image_force_delete"`
 	AlicloudImageForceDeleteSnapshots bool              `mapstructure:"image_force_delete_snapshots"`
 	AlicloudImageForceDeleteInstances bool              `mapstructure:"image_force_delete_instances"`
@@ -40,6 +43,8 @@ type AlicloudImageConfig struct {
 	AlicloudImageSkipRegionValidation bool              `mapstructure:"skip_region_validation"`
 	AlicloudImageTags                 map[string]string `mapstructure:"tags"`
 	AlicloudDiskDevices               `mapstructure:",squash"`
+
+	ImageEncrypted *bool
 }
 
 func (c *AlicloudImageConfig) Prepare(ctx *interpolate.Context) []error {
@@ -75,6 +80,13 @@ func (c *AlicloudImageConfig) Prepare(ctx *interpolate.Context) []error {
 		c.AlicloudImageDestinationRegions = regions
 	}
 
+	c.ImageEncrypted = c.RawImageEncrypted.ToBoolPointer()
+
+	c.ECSSystemDiskMapping.Encrypted = c.RawImageEncrypted.ToBoolPointer()
+	for i := range c.ECSImagesDiskMappings {
+		c.ECSImagesDiskMappings[i].Encrypted = c.RawImageEncrypted.ToBoolPointer()
+	}
+
 	if len(errs) > 0 {
 		return errs
 	}

builder/alicloud/ecs/run_config.go

@@ -8,13 +8,14 @@ import (
 
 	"github.com/hashicorp/packer/common/uuid"
 	"github.com/hashicorp/packer/helper/communicator"
+	"github.com/hashicorp/packer/helper/config"
 	"github.com/hashicorp/packer/template/interpolate"
 )
 
 type RunConfig struct {
 	AssociatePublicIpAddress bool           `mapstructure:"associate_public_ip_address"`
 	ZoneId                   string         `mapstructure:"zone_id"`
-	IOOptimized              *bool  `mapstructure:"io_optimized"`
+	RawIOOptimized           config.Trilean `mapstructure:"io_optimized"`
 	InstanceType             string         `mapstructure:"instance_type"`
 	Description              string         `mapstructure:"description"`
 	AlicloudSourceImage      string         `mapstructure:"source_image"`
@@ -37,6 +38,7 @@ type RunConfig struct {
 	// Communicator settings
 	Comm         communicator.Config `mapstructure:",squash"`
 	SSHPrivateIp bool                `mapstructure:"ssh_private_ip"`
+	IOOptimized  *bool
 }
 
 func (c *RunConfig) Prepare(ctx *interpolate.Context) []error {
@@ -68,5 +70,7 @@ func (c *RunConfig) Prepare(ctx *interpolate.Context) []error {
 		}
 	}
 
+	c.IOOptimized = c.RawIOOptimized.ToBoolPointer()
+
 	return errs
 }

builder/amazon/common/ami_config.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"regexp"
 
+	"github.com/hashicorp/packer/helper/config"
 	"github.com/hashicorp/packer/template/interpolate"
 )
 
@@ -19,17 +20,21 @@ type AMIConfig struct {
 	AMIRegions              []string          `mapstructure:"ami_regions"`
 	AMISkipRegionValidation bool              `mapstructure:"skip_region_validation"`
 	AMITags                 TagMap            `mapstructure:"tags"`
-	AMIENASupport           *bool             `mapstructure:"ena_support"`
+	RawAMIENASupport        config.Trilean    `mapstructure:"ena_support"`
 	AMISriovNetSupport      bool              `mapstructure:"sriov_support"`
 	AMIForceDeregister      bool              `mapstructure:"force_deregister"`
 	AMIForceDeleteSnapshot  bool              `mapstructure:"force_delete_snapshot"`
-	AMIEncryptBootVolume    *bool             `mapstructure:"encrypt_boot"`
+	RawAMIEncryptBootVolume config.Trilean    `mapstructure:"encrypt_boot"`
 	AMIKmsKeyId             string            `mapstructure:"kms_key_id"`
 	AMIRegionKMSKeyIDs      map[string]string `mapstructure:"region_kms_key_ids"`
 	SnapshotTags            TagMap            `mapstructure:"snapshot_tags"`
 	SnapshotUsers           []string          `mapstructure:"snapshot_users"`
 	SnapshotGroups          []string          `mapstructure:"snapshot_groups"`
 	AMISkipBuildRegion      bool              `mapstructure:"skip_save_build_region"`
+
+	// parsed from RawAMIENASupport above. Used in steps.
+	AMIENASupport        *bool
+	AMIEncryptBootVolume *bool
 }
 
 func stringInSlice(s []string, searchstr string) bool {
@@ -60,6 +65,8 @@ func (c *AMIConfig) Prepare(accessConfig *AccessConfig, ctx *interpolate.Context
 
 	errs = append(errs, c.prepareRegions(accessConfig)...)
 
+	c.AMIENASupport = c.RawAMIENASupport.ToBoolPointer()
+	c.AMIEncryptBootVolume = c.RawAMIEncryptBootVolume.ToBoolPointer()
 	// Prevent sharing of default KMS key encrypted volumes with other aws users
 	if len(c.AMIUsers) > 0 {
 		if len(c.AMIKmsKeyId) == 0 && c.AMIEncryptBootVolume != nil && *c.AMIEncryptBootVolume {

builder/amazon/common/ami_config_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/ec2"
 	"github.com/aws/aws-sdk-go/service/ec2/ec2iface"
+	"github.com/hashicorp/packer/helper/config"
 )
 
 func testAMIConfig() *AMIConfig {
@@ -138,7 +139,7 @@ func TestAMIConfigPrepare_regions(t *testing.T) {
 
 	c.SnapshotUsers = []string{"foo", "bar"}
 	c.AMIKmsKeyId = "123-abc-456"
-	c.AMIEncryptBootVolume = &[]bool{true}[0]
+	c.RawAMIEncryptBootVolume = config.TriTrue
 	c.AMIRegions = []string{"us-east-1", "us-west-1"}
 	c.AMIRegionKMSKeyIDs = map[string]string{
 		"us-east-1": "123-456-7890",
@@ -161,7 +162,7 @@ func TestAMIConfigPrepare_regions(t *testing.T) {
 func TestAMIConfigPrepare_Share_EncryptedBoot(t *testing.T) {
 	c := testAMIConfig()
 	c.AMIUsers = []string{"testAccountID"}
-	c.AMIEncryptBootVolume = &[]bool{true}[0]
+	c.RawAMIEncryptBootVolume = config.TriTrue
 
 	accessConf := testAccessConfig()
 

builder/amazon/common/block_device.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/ec2"
+	"github.com/hashicorp/packer/helper/config"
 	"github.com/hashicorp/packer/template/interpolate"
 )
 
@@ -13,7 +14,7 @@ import (
 type BlockDevice struct {
 	DeleteOnTermination bool           `mapstructure:"delete_on_termination"`
 	DeviceName          string         `mapstructure:"device_name"`
-	Encrypted           *bool  `mapstructure:"encrypted"`
+	RawEncrypted        config.Trilean `mapstructure:"encrypted"`
 	IOPS                int64          `mapstructure:"iops"`
 	NoDevice            bool           `mapstructure:"no_device"`
 	SnapshotId          string         `mapstructure:"snapshot_id"`
@@ -23,6 +24,8 @@ type BlockDevice struct {
 	KmsKeyId            string         `mapstructure:"kms_key_id"`
 	// ebssurrogate only
 	OmitFromArtifact bool `mapstructure:"omit_from_artifact"`
+
+	Encrypted *bool
 }
 
 type BlockDevices struct {
@@ -93,6 +96,7 @@ func (b *BlockDevice) Prepare(ctx *interpolate.Context) error {
 		return fmt.Errorf("The `device_name` must be specified " +
 			"for every device in the block device mapping.")
 	}
+	b.Encrypted = b.RawEncrypted.ToBoolPointer()
 	// Warn that encrypted must be true or nil when setting kms_key_id
 	if b.KmsKeyId != "" && b.Encrypted != nil && *b.Encrypted == false {
 		return fmt.Errorf("The device %v, must also have `encrypted: "+

builder/amazon/ebsvolume/builder.go

@@ -24,11 +24,13 @@ type Config struct {
 	awscommon.RunConfig    `mapstructure:",squash"`
 
 	VolumeMappings     []BlockDevice  `mapstructure:"ebs_volumes"`
-	AMIENASupport      *bool         `mapstructure:"ena_support"`
+	RawAMIENASupport   config.Trilean `mapstructure:"ena_support"`
 	AMISriovNetSupport bool           `mapstructure:"sriov_support"`
 
 	launchBlockDevices awscommon.BlockDevices
 	ctx                interpolate.Context
+
+	AMIENASupport *bool
 }
 
 type Builder struct {
@@ -75,6 +77,8 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 		errs = packer.MultiErrorAppend(errs, err)
 	}
 
+	b.config.AMIENASupport = b.config.RawAMIENASupport.ToBoolPointer()
+
 	if b.config.IsSpotInstance() && ((b.config.AMIENASupport != nil && *b.config.AMIENASupport) || b.config.AMISriovNetSupport) {
 		errs = packer.MultiErrorAppend(errs,
 			fmt.Errorf("Spot instances do not support modification, which is required "+

helper/config/custom_types.go

@@ -0,0 +1,72 @@
+package config
+
+import (
+	"strconv"
+)
+
+type Trilean uint8
+
+const (
+	// This will assign unset to 0, which is the default value in interpolation
+	TriUnset Trilean = iota
+	TriTrue
+	TriFalse
+)
+
+func (t Trilean) ToString() string {
+	if t == TriTrue {
+		return "TriTrue"
+	} else if t == TriFalse {
+		return "TriFalse"
+	}
+	return "TriUnset"
+}
+
+func (t Trilean) ToBoolPointer() *bool {
+	if t == TriTrue {
+		return boolPointer(true)
+	} else if t == TriFalse {
+		return boolPointer(false)
+	}
+	return nil
+}
+
+func (t Trilean) True() bool {
+	if t == TriTrue {
+		return true
+	}
+	return false
+}
+
+func (t Trilean) False() bool {
+	if t == TriFalse {
+		return true
+	}
+	return false
+}
+
+func TrileanFromString(s string) (Trilean, error) {
+	if s == "" {
+		return TriUnset, nil
+	}
+
+	b, err := strconv.ParseBool(s)
+	if err != nil {
+		return TriUnset, err
+	} else if b == true {
+		return TriTrue, nil
+	} else {
+		return TriFalse, nil
+	}
+}
+
+func TrileanFromBool(b bool) Trilean {
+	if b {
+		return TriTrue
+	}
+	return TriFalse
+}
+
+func boolPointer(b bool) *bool {
+	return &b
+}

helper/config/custom_types_test.go

@@ -0,0 +1,30 @@
+package config
+
+import (
+	"testing"
+)
+
+func TestTrilianParsing(t *testing.T) {
+	type testCase struct {
+		Input       string
+		Output      Trilean
+		ErrExpected bool
+	}
+	testCases := []testCase{
+		{"true", TriTrue, false}, {"True", TriTrue, false},
+		{"false", TriFalse, false}, {"False", TriFalse, false},
+		{"", TriUnset, false}, {"badvalue", TriUnset, true},
+		{"FAlse", TriUnset, true}, {"TrUe", TriUnset, true},
+	}
+	for _, tc := range testCases {
+		tril, err := TrileanFromString(tc.Input)
+		if err != nil {
+			if tc.ErrExpected == false {
+				t.Fatalf("Didn't expect error: %v", tc)
+			}
+		}
+		if tc.Output != tril {
+			t.Fatalf("Didn't return proper trilean. %v", tc)
+		}
+	}
+}

helper/config/decode.go

@@ -29,6 +29,7 @@ type DecodeOpts struct {
 
 var DefaultDecodeHookFuncs = []mapstructure.DecodeHookFunc{
 	uint8ToStringHook,
+	stringToTrilean,
 	mapstructure.StringToSliceHookFunc(","),
 	mapstructure.StringToTimeDurationHookFunc(),
 }
@@ -154,3 +155,30 @@ func uint8ToStringHook(f reflect.Kind, t reflect.Kind, v interface{}) (interface
 
 	return v, nil
 }
+
+func stringToTrilean(f reflect.Type, t reflect.Type, v interface{}) (interface{}, error) {
+	// We have a custom data type, config, which we read from a string and
+	// then cast to a *bool. Why? So that we can appropriately read "unset"
+	// *bool values in order to intelligently default, even when the values are
+	// being set by a template variable.
+
+	testTril, _ := TrileanFromString("")
+	if t == reflect.TypeOf(testTril) {
+		// From value is string
+		if f == reflect.TypeOf("") {
+			tril, err := TrileanFromString(v.(string))
+			if err != nil {
+				return v, fmt.Errorf("Error parsing bool from given var: %s", err)
+			}
+			return tril, nil
+		} else {
+			// From value is boolean
+			if f == reflect.TypeOf(true) {
+				tril := TrileanFromBool(v.(bool))
+				return tril, nil
+			}
+		}
+
+	}
+	return v, nil
+}