command+backend: generalized "plan mode"

So far we've only had "normal mode" and "destroy mode", where the latter
is activated either by "terraform plan -destroy" or "terraform destroy".

In preparation for introducing a third mode "refresh only" this
generalizes how we handle modes so we can potentially deal with an
arbitrary number of modes, although for now we only intend to have three.

Mostly this is just a different implementation of the same old behavior,
but there is one small user-visible difference here: the "terraform apply"
command now accepts a -destroy option, mirroring the option of the same
name on "terraform plan", which in turn makes "terraform destroy"
effectively a shorthand for "terraform apply -destroy".

This is intended to make us consistent that "terraform apply" without a
plan file argument accepts all of the same plan-customization options that
"terraform plan" does, which will in turn avoid us having to add a new
alias of "terraform plan" for each new plan mode we might add. The -help
output is changed in that vein here, although we'll wait for subsequent
commit to make a similar change to the website documentation just so we
can deal with the "refresh only mode" docs at the same time.

backend/backend.go

@@ -193,8 +193,8 @@ type Operation struct {
 
 	// The options below are more self-explanatory and affect the runtime
 	// behavior of the operation.
+	PlanMode    plans.Mode
 	AutoApprove bool
-	Destroy     bool
 	Parallelism int
 	Targets     []addrs.Targetable
 	Variables   map[string]UnparsedVariableValue

backend/local/backend_apply.go

@@ -8,6 +8,7 @@ import (
 	"github.com/hashicorp/errwrap"
 	"github.com/hashicorp/terraform/backend"
 	"github.com/hashicorp/terraform/command/views"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/states"
 	"github.com/hashicorp/terraform/states/statefile"
 	"github.com/hashicorp/terraform/states/statemgr"
@@ -26,7 +27,7 @@ func (b *Local) opApply(
 
 	// If we have a nil module at this point, then set it to an empty tree
 	// to avoid any potential crashes.
-	if op.PlanFile == nil && !op.Destroy && !op.HasConfig() {
+	if op.PlanFile == nil && op.PlanMode != plans.DestroyMode && !op.HasConfig() {
 		diags = diags.Append(tfdiags.Sourceless(
 			tfdiags.Error,
 			"No configuration files",
@@ -76,7 +77,7 @@ func (b *Local) opApply(
 		mustConfirm := hasUI && !op.AutoApprove && !trivialPlan
 		if mustConfirm {
 			var desc, query string
-			if op.Destroy {
+			if op.PlanMode == plans.DestroyMode {
 				if op.Workspace != "default" {
 					query = "Do you really want to destroy all resources in workspace \"" + op.Workspace + "\"?"
 				} else {
@@ -116,7 +117,7 @@ func (b *Local) opApply(
 				return
 			}
 			if v != "yes" {
-				op.View.Cancelled(op.Destroy)
+				op.View.Cancelled(op.PlanMode)
 				runningOp.Result = backend.OperationFailure
 				return
 			}

backend/local/backend_apply_test.go

@@ -18,6 +18,7 @@ import (
 	"github.com/hashicorp/terraform/configs/configschema"
 	"github.com/hashicorp/terraform/internal/initwd"
 	"github.com/hashicorp/terraform/internal/terminal"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/providers"
 	"github.com/hashicorp/terraform/states"
 	"github.com/hashicorp/terraform/states/statemgr"
@@ -115,7 +116,7 @@ func TestLocal_applyEmptyDirDestroy(t *testing.T) {
 
 	op, configCleanup, done := testOperationApply(t, "./testdata/empty")
 	defer configCleanup()
-	op.Destroy = true
+	op.PlanMode = plans.DestroyMode
 
 	run, err := b.Operation(context.Background(), op)
 	if err != nil {

backend/local/backend_local.go

@@ -10,7 +10,6 @@ import (
 	"github.com/hashicorp/terraform/backend"
 	"github.com/hashicorp/terraform/configs"
 	"github.com/hashicorp/terraform/configs/configload"
-	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/plans/planfile"
 	"github.com/hashicorp/terraform/states/statemgr"
 	"github.com/hashicorp/terraform/terraform"
@@ -66,12 +65,7 @@ func (b *Local) context(op *backend.Operation) (*terraform.Context, *configload.
 	}
 
 	// Copy set options from the operation
-	switch {
+	opts.PlanMode = op.PlanMode
-	case op.Destroy:
-		opts.PlanMode = plans.DestroyMode
-	default:
-		opts.PlanMode = plans.NormalMode
-	}
 	opts.Targets = op.Targets
 	opts.UIInput = op.UIIn
 	opts.Hooks = op.Hooks

backend/local/backend_plan.go

@@ -35,7 +35,7 @@ func (b *Local) opPlan(
 	}
 
 	// Local planning requires a config, unless we're planning to destroy.
-	if !op.Destroy && !op.HasConfig() {
+	if op.PlanMode != plans.DestroyMode && !op.HasConfig() {
 		diags = diags.Append(tfdiags.Sourceless(
 			tfdiags.Error,
 			"No configuration files",

backend/local/backend_plan_test.go

@@ -544,7 +544,7 @@ func TestLocal_planDestroy(t *testing.T) {
 
 	op, configCleanup, done := testOperationPlan(t, "./testdata/plan")
 	defer configCleanup()
-	op.Destroy = true
+	op.PlanMode = plans.DestroyMode
 	op.PlanRefresh = true
 	op.PlanOutPath = planPath
 	cfg := cty.ObjectVal(map[string]cty.Value{
@@ -598,7 +598,7 @@ func TestLocal_planDestroy_withDataSources(t *testing.T) {
 
 	op, configCleanup, done := testOperationPlan(t, "./testdata/destroy-with-ds")
 	defer configCleanup()
-	op.Destroy = true
+	op.PlanMode = plans.DestroyMode
 	op.PlanRefresh = true
 	op.PlanOutPath = planPath
 	cfg := cty.ObjectVal(map[string]cty.Value{

backend/remote/backend_apply.go

@@ -10,6 +10,7 @@ import (
 	tfe "github.com/hashicorp/go-tfe"
 	version "github.com/hashicorp/go-version"
 	"github.com/hashicorp/terraform/backend"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/hashicorp/terraform/tfdiags"
 )
@@ -84,7 +85,7 @@ func (b *Remote) opApply(stopCtx, cancelCtx context.Context, op *backend.Operati
 		))
 	}
 
-	if !op.HasConfig() && !op.Destroy {
+	if !op.HasConfig() && op.PlanMode != plans.DestroyMode {
 		diags = diags.Append(tfdiags.Sourceless(
 			tfdiags.Error,
 			"No configuration files found",
@@ -152,10 +153,12 @@ func (b *Remote) opApply(stopCtx, cancelCtx context.Context, op *backend.Operati
 		if r.Actions.IsDiscardable {
 			err = b.client.Runs.Discard(stopCtx, r.ID, tfe.RunDiscardOptions{})
 			if err != nil {
-				if op.Destroy {
+				switch op.PlanMode {
+				case plans.DestroyMode:
 					return r, generalError("Failed to discard destroy", err)
+				default:
+					return r, generalError("Failed to discard apply", err)
 				}
-				return r, generalError("Failed to discard apply", err)
 			}
 		}
 		diags = diags.Append(tfdiags.Sourceless(
@@ -176,7 +179,7 @@ func (b *Remote) opApply(stopCtx, cancelCtx context.Context, op *backend.Operati
 		if mustConfirm {
 			opts := &terraform.InputOpts{Id: "approve"}
 
-			if op.Destroy {
+			if op.PlanMode == plans.DestroyMode {
 				opts.Query = "\nDo you really want to destroy all resources in workspace \"" + op.Workspace + "\"?"
 				opts.Description = "Terraform will destroy all your managed infrastructure, as shown above.\n" +
 					"There is no undo. Only 'yes' will be accepted to confirm."

backend/remote/backend_apply_test.go

@@ -19,6 +19,7 @@ import (
 	"github.com/hashicorp/terraform/command/views"
 	"github.com/hashicorp/terraform/internal/initwd"
 	"github.com/hashicorp/terraform/internal/terminal"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/plans/planfile"
 	"github.com/hashicorp/terraform/states/statemgr"
 	"github.com/hashicorp/terraform/terraform"
@@ -968,7 +969,7 @@ func TestRemote_applyDestroy(t *testing.T) {
 		"approve": "yes",
 	})
 
-	op.Destroy = true
+	op.PlanMode = plans.DestroyMode
 	op.UIIn = input
 	op.UIOut = b.CLI
 	op.Workspace = backend.DefaultStateName
@@ -1014,7 +1015,7 @@ func TestRemote_applyDestroyNoConfig(t *testing.T) {
 	defer configCleanup()
 	defer done(t)
 
-	op.Destroy = true
+	op.PlanMode = plans.DestroyMode
 	op.UIIn = input
 	op.UIOut = b.CLI
 	op.Workspace = backend.DefaultStateName

backend/remote/backend_common.go

@@ -13,6 +13,7 @@ import (
 
 	tfe "github.com/hashicorp/go-tfe"
 	"github.com/hashicorp/terraform/backend"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/terraform"
 )
 
@@ -508,7 +509,7 @@ func (b *Remote) confirm(stopCtx context.Context, op *backend.Operation, opts *t
 
 					if err == errRunDiscarded {
 						err = errApplyDiscarded
-						if op.Destroy {
+						if op.PlanMode == plans.DestroyMode {
 							err = errDestroyDiscarded
 						}
 					}
@@ -551,7 +552,7 @@ func (b *Remote) confirm(stopCtx context.Context, op *backend.Operation, opts *t
 			if r.Actions.IsDiscardable {
 				err = b.client.Runs.Discard(stopCtx, r.ID, tfe.RunDiscardOptions{})
 				if err != nil {
-					if op.Destroy {
+					if op.PlanMode == plans.DestroyMode {
 						return generalError("Failed to discard destroy", err)
 					}
 					return generalError("Failed to discard apply", err)
@@ -560,7 +561,7 @@ func (b *Remote) confirm(stopCtx context.Context, op *backend.Operation, opts *t
 
 			// Even if the run was discarded successfully, we still
 			// return an error as the apply command was canceled.
-			if op.Destroy {
+			if op.PlanMode == plans.DestroyMode {
 				return errDestroyDiscarded
 			}
 			return errApplyDiscarded

backend/remote/backend_context.go

@@ -12,7 +12,6 @@ import (
 	"github.com/hashicorp/hcl/v2/hclsyntax"
 	"github.com/hashicorp/terraform/backend"
 	"github.com/hashicorp/terraform/configs"
-	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/states/statemgr"
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/hashicorp/terraform/tfdiags"
@@ -62,12 +61,7 @@ func (b *Remote) Context(op *backend.Operation) (*terraform.Context, statemgr.Fu
 	}
 
 	// Copy set options from the operation
-	switch {
+	opts.PlanMode = op.PlanMode
-	case op.Destroy:
-		opts.PlanMode = plans.DestroyMode
-	default:
-		opts.PlanMode = plans.NormalMode
-	}
 	opts.Targets = op.Targets
 	opts.UIInput = op.UIIn
 

backend/remote/backend_plan.go

@@ -17,6 +17,7 @@ import (
 	tfe "github.com/hashicorp/go-tfe"
 	version "github.com/hashicorp/go-version"
 	"github.com/hashicorp/terraform/backend"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/tfdiags"
 )
 
@@ -89,7 +90,7 @@ func (b *Remote) opPlan(stopCtx, cancelCtx context.Context, op *backend.Operatio
 		))
 	}
 
-	if !op.HasConfig() && !op.Destroy {
+	if !op.HasConfig() && op.PlanMode != plans.DestroyMode {
 		diags = diags.Append(tfdiags.Sourceless(
 			tfdiags.Error,
 			"No configuration files found",
@@ -238,12 +239,26 @@ in order to capture the filesystem context the remote workspace expects:
 	}
 
 	runOptions := tfe.RunCreateOptions{
-		IsDestroy:            tfe.Bool(op.Destroy),
 		Message:              tfe.String(queueMessage),
 		ConfigurationVersion: cv,
 		Workspace:            w,
 	}
 
+	switch op.PlanMode {
+	case plans.NormalMode:
+		// okay, but we don't need to do anything special for this
+	case plans.DestroyMode:
+		runOptions.IsDestroy = tfe.Bool(true)
+	default:
+		// Shouldn't get here because we should update this for each new
+		// plan mode we add, mapping it to the corresponding RunCreateOptions
+		// field.
+		return nil, generalError(
+			"Invalid plan mode",
+			fmt.Errorf("remote backend doesn't support %s", op.PlanMode),
+		)
+	}
+
 	if len(op.Targets) != 0 {
 		runOptions.TargetAddrs = make([]string, 0, len(op.Targets))
 		for _, addr := range op.Targets {

backend/remote/backend_plan_test.go

@@ -18,6 +18,7 @@ import (
 	"github.com/hashicorp/terraform/command/views"
 	"github.com/hashicorp/terraform/internal/initwd"
 	"github.com/hashicorp/terraform/internal/terminal"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/plans/planfile"
 	"github.com/hashicorp/terraform/states/statemgr"
 	"github.com/hashicorp/terraform/terraform"
@@ -709,7 +710,7 @@ func TestRemote_planDestroy(t *testing.T) {
 	defer configCleanup()
 	defer done(t)
 
-	op.Destroy = true
+	op.PlanMode = plans.DestroyMode
 	op.Workspace = backend.DefaultStateName
 
 	run, err := b.Operation(context.Background(), op)
@@ -734,7 +735,7 @@ func TestRemote_planDestroyNoConfig(t *testing.T) {
 	defer configCleanup()
 	defer done(t)
 
-	op.Destroy = true
+	op.PlanMode = plans.DestroyMode
 	op.Workspace = backend.DefaultStateName
 
 	run, err := b.Operation(context.Background(), op)

command/apply.go

@@ -23,6 +23,8 @@ type ApplyCommand struct {
 }
 
 func (c *ApplyCommand) Run(rawArgs []string) int {
+	var diags tfdiags.Diagnostics
+
 	// Parse and apply global view arguments
 	common, rawArgs := arguments.ParseView(rawArgs)
 	c.View.Configure(common)
@@ -33,7 +35,13 @@ func (c *ApplyCommand) Run(rawArgs []string) int {
 	c.Meta.Color = c.Meta.color
 
 	// Parse and validate flags
-	args, diags := arguments.ParseApply(rawArgs)
+	var args *arguments.Apply
+	switch {
+	case c.Destroy:
+		args, diags = arguments.ParseApplyDestroy(rawArgs)
+	default:
+		args, diags = arguments.ParseApply(rawArgs)
+	}
 
 	// Instantiate the view, even if there are flag errors, so that we render
 	// diagnostics according to the desired view
@@ -253,7 +261,7 @@ func (c *ApplyCommand) OperationRequest(
 	opReq := c.Operation(be)
 	opReq.AutoApprove = autoApprove
 	opReq.ConfigDir = "."
-	opReq.Destroy = c.Destroy
+	opReq.PlanMode = args.PlanMode
 	opReq.Hooks = view.Hooks()
 	opReq.PlanFile = planFile
 	opReq.PlanRefresh = args.Refresh
@@ -345,9 +353,6 @@ Options:
   -parallelism=n         Limit the number of parallel resource operations.
                          Defaults to 10.
 
-  -refresh=true          Update state prior to checking for differences. This
-                         has no effect if a plan file is given to apply.
-
   -state=path            Path to read and save state (unless state-out
                          is specified). Defaults to "terraform.tfstate".
 
@@ -355,18 +360,10 @@ Options:
                          "-state". This can be used to preserve the old
                          state.
 
-  -target=resource       Resource to target. Operation will be limited to this
+  If you don't provide a saved plan file then this command will also accept
-                         resource and its dependencies. This flag can be used
+  all of the plan-customization options accepted by the terraform plan command.
-                         multiple times.
+  For more information on those options, run:
-
+      terraform plan -help
-  -var 'foo=bar'         Set a variable in the Terraform configuration. This
-                         flag can be set multiple times.
-
-  -var-file=foo          Set variables in the Terraform configuration from
-                         a file. If "terraform.tfvars" or any ".auto.tfvars"
-                         files are present, they will be automatically loaded.
-
-
 `
 	return strings.TrimSpace(helpText)
 }
@@ -377,35 +374,12 @@ Usage: terraform [global options] destroy [options]
 
   Destroy Terraform-managed infrastructure.
 
-Options:
+  This command is a convenience alias for:
+      terraform apply -destroy
 
-  -auto-approve          Skip interactive approval before destroying.
+  This command also accepts many of the plan-customization options accepted by
-
+  the terraform plan command. For more information on those options, run:
-  -lock=true             Lock the state file when locking is supported.
+      terraform plan -help
-
-  -lock-timeout=0s       Duration to retry a state lock.
-
-  -no-color              If specified, output won't contain any color.
-
-  -parallelism=n         Limit the number of concurrent operations.
-                         Defaults to 10.
-
-  -refresh=true          Update state prior to checking for differences. This
-                         has no effect if a plan file is given to apply.
-
-  -target=resource       Resource to target. Operation will be limited to this
-                         resource and its dependencies. This flag can be used
-                         multiple times.
-
-  -var 'foo=bar'         Set a variable in the Terraform configuration. This
-                         flag can be set multiple times.
-
-  -var-file=foo          Set variables in the Terraform configuration from
-                         a file. If "terraform.tfvars" or any ".auto.tfvars"
-                         files are present, they will be automatically loaded.
-
-  -state, state-out, and -backup are legacy options supported for the local
-  backend only. For more information, see the local backend's documentation.
 `
 	return strings.TrimSpace(helpText)
 }

command/arguments/apply.go

@@ -1,6 +1,9 @@
 package arguments
 
 import (
+	"fmt"
+
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/tfdiags"
 )
 
@@ -71,3 +74,53 @@ func ParseApply(args []string) (*Apply, tfdiags.Diagnostics) {
 
 	return apply, diags
 }
+
+// ParseApplyDestroy is a special case of ParseApply that deals with the
+// "terraform destroy" command, which is effectively an alias for
+// "terraform apply -destroy".
+func ParseApplyDestroy(args []string) (*Apply, tfdiags.Diagnostics) {
+	apply, diags := ParseApply(args)
+
+	// So far ParseApply was using the command line options like -destroy
+	// and -refresh-only to determine the plan mode. For "terraform destroy"
+	// we expect neither of those arguments to be set, and so the plan mode
+	// should currently be set to NormalMode, which we'll replace with
+	// DestroyMode here. If it's already set to something else then that
+	// suggests incorrect usage.
+	switch apply.Operation.PlanMode {
+	case plans.NormalMode:
+		// This indicates that the user didn't specify any mode options at
+		// all, which is correct, although we know from the command that
+		// they actually intended to use DestroyMode here.
+		apply.Operation.PlanMode = plans.DestroyMode
+	case plans.DestroyMode:
+		diags = diags.Append(tfdiags.Sourceless(
+			tfdiags.Error,
+			"Invalid mode option",
+			"The -destroy option is not valid for \"terraform destroy\", because this command always runs in destroy mode.",
+		))
+	case plans.RefreshOnlyMode:
+		diags = diags.Append(tfdiags.Sourceless(
+			tfdiags.Error,
+			"Invalid mode option",
+			"The -refresh-only option is not valid for \"terraform destroy\".",
+		))
+	default:
+		// This is a non-ideal error message for if we forget to handle a
+		// newly-handled plan mode in Operation.Parse. Ideally they should all
+		// have cases above so we can produce better error messages.
+		diags = diags.Append(tfdiags.Sourceless(
+			tfdiags.Error,
+			"Invalid mode option",
+			fmt.Sprintf("The \"terraform destroy\" command doesn't support %s.", apply.Operation.PlanMode),
+		))
+	}
+
+	// NOTE: It's also invalid to have apply.PlanPath set in this codepath,
+	// but we don't check that in here because we'll return a different error
+	// message depending on whether the given path seems to refer to a saved
+	// plan file or to a configuration directory. The apply command
+	// implementation itself therefore handles this situation.
+
+	return apply, diags
+}

command/arguments/apply_test.go

@@ -5,7 +5,9 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
 	"github.com/hashicorp/terraform/addrs"
+	"github.com/hashicorp/terraform/plans"
 )
 
 func TestParseApply_basicValid(t *testing.T) {
@@ -20,6 +22,13 @@ func TestParseApply_basicValid(t *testing.T) {
 				InputEnabled: true,
 				PlanPath:     "",
 				ViewType:     ViewHuman,
+				State:        &State{Lock: true},
+				Vars:         &Vars{},
+				Operation: &Operation{
+					PlanMode:    plans.NormalMode,
+					Parallelism: 10,
+					Refresh:     true,
+				},
 			},
 		},
 		"auto-approve, disabled input, and plan path": {
@@ -29,22 +38,43 @@ func TestParseApply_basicValid(t *testing.T) {
 				InputEnabled: false,
 				PlanPath:     "saved.tfplan",
 				ViewType:     ViewHuman,
+				State:        &State{Lock: true},
+				Vars:         &Vars{},
+				Operation: &Operation{
+					PlanMode:    plans.NormalMode,
+					Parallelism: 10,
+					Refresh:     true,
+				},
+			},
+		},
+		"destroy mode": {
+			[]string{"-destroy"},
+			&Apply{
+				AutoApprove:  false,
+				InputEnabled: true,
+				PlanPath:     "",
+				ViewType:     ViewHuman,
+				State:        &State{Lock: true},
+				Vars:         &Vars{},
+				Operation: &Operation{
+					PlanMode:    plans.DestroyMode,
+					Parallelism: 10,
+					Refresh:     true,
+				},
 			},
 		},
 	}
 
+	cmpOpts := cmpopts.IgnoreUnexported(Operation{}, Vars{}, State{})
+
 	for name, tc := range testCases {
 		t.Run(name, func(t *testing.T) {
 			got, diags := ParseApply(tc.args)
 			if len(diags) > 0 {
 				t.Fatalf("unexpected diags: %v", diags)
 			}
-			// Ignore the extended arguments for simplicity
+			if diff := cmp.Diff(tc.want, got, cmpOpts); diff != "" {
-			got.State = nil
+				t.Errorf("unexpected result\n%s", diff)
-			got.Operation = nil
-			got.Vars = nil
-			if *got != *tc.want {
-				t.Fatalf("unexpected result\n got: %#v\nwant: %#v", got, tc.want)
 			}
 		})
 	}
@@ -175,3 +205,70 @@ func TestParseApply_vars(t *testing.T) {
 		})
 	}
 }
+
+func TestParseApplyDestroy_basicValid(t *testing.T) {
+	testCases := map[string]struct {
+		args []string
+		want *Apply
+	}{
+		"defaults": {
+			nil,
+			&Apply{
+				AutoApprove:  false,
+				InputEnabled: true,
+				ViewType:     ViewHuman,
+				State:        &State{Lock: true},
+				Vars:         &Vars{},
+				Operation: &Operation{
+					PlanMode:    plans.DestroyMode,
+					Parallelism: 10,
+					Refresh:     true,
+				},
+			},
+		},
+		"auto-approve and disabled input": {
+			[]string{"-auto-approve", "-input=false"},
+			&Apply{
+				AutoApprove:  true,
+				InputEnabled: false,
+				ViewType:     ViewHuman,
+				State:        &State{Lock: true},
+				Vars:         &Vars{},
+				Operation: &Operation{
+					PlanMode:    plans.DestroyMode,
+					Parallelism: 10,
+					Refresh:     true,
+				},
+			},
+		},
+	}
+
+	cmpOpts := cmpopts.IgnoreUnexported(Operation{}, Vars{}, State{})
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			got, diags := ParseApplyDestroy(tc.args)
+			if len(diags) > 0 {
+				t.Fatalf("unexpected diags: %v", diags)
+			}
+			if diff := cmp.Diff(tc.want, got, cmpOpts); diff != "" {
+				t.Errorf("unexpected result\n%s", diff)
+			}
+		})
+	}
+}
+
+func TestParseApplyDestroy_invalid(t *testing.T) {
+	t.Run("explicit destroy mode", func(t *testing.T) {
+		got, diags := ParseApplyDestroy([]string{"-destroy"})
+		if len(diags) == 0 {
+			t.Fatal("expected diags but got none")
+		}
+		if got, want := diags.Err().Error(), "Invalid mode option:"; !strings.Contains(got, want) {
+			t.Fatalf("wrong diags\n got: %s\nwant: %s", got, want)
+		}
+		if got.ViewType != ViewHuman {
+			t.Fatalf("wrong view type, got %#v, want %#v", got.ViewType, ViewHuman)
+		}
+	})
+}

command/arguments/extended.go

@@ -8,6 +8,7 @@ import (
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/hcl/v2/hclsyntax"
 	"github.com/hashicorp/terraform/addrs"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/tfdiags"
 )
 
@@ -45,6 +46,11 @@ type State struct {
 // Operation describes arguments which are used to configure how a Terraform
 // operation such as a plan or apply executes.
 type Operation struct {
+	// PlanMode selects one of the mutually-exclusive planning modes that
+	// decides the overall goal of a plan operation. This field is relevant
+	// only for an operation that produces a plan.
+	PlanMode plans.Mode
+
 	// Parallelism is the limit Terraform places on total parallel operations
 	// as it walks the dependency graph.
 	Parallelism int
@@ -57,7 +63,11 @@ type Operation struct {
 	// their dependencies.
 	Targets []addrs.Targetable
 
+	// These private fields are used only temporarily during decoding. Use
+	// method Parse to populate the exported fields from these, validating
+	// the raw values in the process.
 	targetsRaw []string
+	destroyRaw bool
 }
 
 // Parse must be called on Operation after initial flag parse. This processes
@@ -92,6 +102,15 @@ func (o *Operation) Parse() tfdiags.Diagnostics {
 		o.Targets = append(o.Targets, target.Subject)
 	}
 
+	// If you add a new possible value for o.PlanMode here, consider also
+	// adding a specialized error message for it in ParseApplyDestroy.
+	switch {
+	case o.destroyRaw:
+		o.PlanMode = plans.DestroyMode
+	default:
+		o.PlanMode = plans.NormalMode
+	}
+
 	return diags
 }
 
@@ -140,6 +159,7 @@ func extendedFlagSet(name string, state *State, operation *Operation, vars *Vars
 	if operation != nil {
 		f.IntVar(&operation.Parallelism, "parallelism", DefaultParallelism, "parallelism")
 		f.BoolVar(&operation.Refresh, "refresh", true, "refresh")
+		f.BoolVar(&operation.destroyRaw, "destroy", false, "destroy")
 		f.Var((*flagStringSlice)(&operation.targetsRaw), "target", "target")
 	}
 

command/arguments/plan.go

@@ -11,9 +11,6 @@ type Plan struct {
 	Operation *Operation
 	Vars      *Vars
 
-	// Destroy can be set to generate a plan to destroy all infrastructure.
-	Destroy bool
-
 	// DetailedExitCode enables different exit codes for error, success with
 	// changes, and success with no changes.
 	DetailedExitCode bool
@@ -41,7 +38,6 @@ func ParsePlan(args []string) (*Plan, tfdiags.Diagnostics) {
 	}
 
 	cmdFlags := extendedFlagSet("plan", plan.State, plan.Operation, plan.Vars)
-	cmdFlags.BoolVar(&plan.Destroy, "destroy", false, "destroy")
 	cmdFlags.BoolVar(&plan.DetailedExitCode, "detailed-exitcode", false, "detailed-exitcode")
 	cmdFlags.BoolVar(&plan.InputEnabled, "input", true, "input")
 	cmdFlags.StringVar(&plan.OutPath, "out", "", "out")

command/arguments/plan_test.go

@@ -5,7 +5,9 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
 	"github.com/hashicorp/terraform/addrs"
+	"github.com/hashicorp/terraform/plans"
 )
 
 func TestParsePlan_basicValid(t *testing.T) {
@@ -16,37 +18,47 @@ func TestParsePlan_basicValid(t *testing.T) {
 		"defaults": {
 			nil,
 			&Plan{
-				Destroy:          false,
 				DetailedExitCode: false,
 				InputEnabled:     true,
 				OutPath:          "",
 				ViewType:         ViewHuman,
+				State:            &State{Lock: true},
+				Vars:             &Vars{},
+				Operation: &Operation{
+					PlanMode:    plans.NormalMode,
+					Parallelism: 10,
+					Refresh:     true,
+				},
 			},
 		},
 		"setting all options": {
 			[]string{"-destroy", "-detailed-exitcode", "-input=false", "-out=saved.tfplan"},
 			&Plan{
-				Destroy:          true,
 				DetailedExitCode: true,
 				InputEnabled:     false,
 				OutPath:          "saved.tfplan",
 				ViewType:         ViewHuman,
+				State:            &State{Lock: true},
+				Vars:             &Vars{},
+				Operation: &Operation{
+					PlanMode:    plans.DestroyMode,
+					Parallelism: 10,
+					Refresh:     true,
+				},
 			},
 		},
 	}
 
+	cmpOpts := cmpopts.IgnoreUnexported(Operation{}, Vars{}, State{})
+
 	for name, tc := range testCases {
 		t.Run(name, func(t *testing.T) {
 			got, diags := ParsePlan(tc.args)
 			if len(diags) > 0 {
 				t.Fatalf("unexpected diags: %v", diags)
 			}
-			// Ignore the extended arguments for simplicity
+			if diff := cmp.Diff(tc.want, got, cmpOpts); diff != "" {
-			got.State = nil
+				t.Errorf("unexpected result\n%s", diff)
-			got.Operation = nil
-			got.Vars = nil
-			if *got != *tc.want {
-				t.Fatalf("unexpected result\n got: %#v\nwant: %#v", got, tc.want)
 			}
 		})
 	}

command/plan.go

@@ -71,7 +71,7 @@ func (c *PlanCommand) Run(rawArgs []string) int {
 	}
 
 	// Build the operation request
-	opReq, opDiags := c.OperationRequest(be, view, args.Operation, args.Destroy, args.OutPath)
+	opReq, opDiags := c.OperationRequest(be, view, args.Operation, args.OutPath)
 	diags = diags.Append(opDiags)
 	if diags.HasErrors() {
 		view.Diagnostics(diags)
@@ -137,7 +137,6 @@ func (c *PlanCommand) OperationRequest(
 	be backend.Enhanced,
 	view views.Plan,
 	args *arguments.Operation,
-	destroy bool,
 	planOutPath string,
 ) (*backend.Operation, tfdiags.Diagnostics) {
 	var diags tfdiags.Diagnostics
@@ -145,7 +144,7 @@ func (c *PlanCommand) OperationRequest(
 	// Build the operation
 	opReq := c.Operation(be)
 	opReq.ConfigDir = "."
-	opReq.Destroy = destroy
+	opReq.PlanMode = args.PlanMode
 	opReq.Hooks = view.Hooks()
 	opReq.PlanRefresh = args.Refresh
 	opReq.PlanOutPath = planOutPath
@@ -196,15 +195,34 @@ Usage: terraform [global options] plan [options]
   You can optionally save the plan to a file, which you can then pass to
   the "apply" command to perform exactly the actions described in the plan.
 
-Options:
+Plan Customization Options:
+
+  The following options customize how Terraform will produce its plan. You
+  can also use these options when you run "terraform apply" without passing
+  it a saved plan, in order to plan and apply in a single command.
+
+  -destroy            If set, a plan will be generated to destroy all resources
+                      managed by the given configuration and state.
+
+  -refresh=true       Update state prior to checking for differences.
+
+  -target=resource    Resource to target. Operation will be limited to this
+                      resource and its dependencies. This flag can be used
+                      multiple times.
+
+  -var 'foo=bar'      Set a variable in the Terraform configuration. This
+                      flag can be set multiple times.
+
+  -var-file=foo       Set variables in the Terraform configuration from
+                      a file. If "terraform.tfvars" or any ".auto.tfvars"
+                      files are present, they will be automatically loaded.
+
+Other Options:
 
   -compact-warnings   If Terraform produces any warnings that are not
                       accompanied by errors, show them in a more compact form
                       that includes only the summary messages.
 
-  -destroy            If set, a plan will be generated to destroy all resources
-                      managed by the given configuration and state.
-
   -detailed-exitcode  Return detailed exit codes when the command exits. This
                       will change the meaning of exit codes to:
                       0 - Succeeded, diff is empty (no changes)
@@ -224,21 +242,8 @@ Options:
 
   -parallelism=n      Limit the number of concurrent operations. Defaults to 10.
 
-  -refresh=true       Update state prior to checking for differences.
-
   -state=statefile    A legacy option used for the local backend only. See the
                       local backend's documentation for more information.
-
-  -target=resource    Resource to target. Operation will be limited to this
-                      resource and its dependencies. This flag can be used
-                      multiple times.
-
-  -var 'foo=bar'      Set a variable in the Terraform configuration. This
-                      flag can be set multiple times.
-
-  -var-file=foo       Set variables in the Terraform configuration from
-                      a file. If "terraform.tfvars" or any ".auto.tfvars"
-                      files are present, they will be automatically loaded.
 `
 	return strings.TrimSpace(helpText)
 }

command/views/operation.go

@@ -18,7 +18,7 @@ type Operation interface {
 	Interrupted()
 	FatalInterrupt()
 	Stopping()
-	Cancelled(destroy bool)
+	Cancelled(planMode plans.Mode)
 
 	EmergencyDumpState(stateFile *statefile.File) error
 
@@ -75,10 +75,11 @@ func (v *OperationHuman) Stopping() {
 	v.view.streams.Println("Stopping operation...")
 }
 
-func (v *OperationHuman) Cancelled(destroy bool) {
+func (v *OperationHuman) Cancelled(planMode plans.Mode) {
-	if destroy {
+	switch planMode {
+	case plans.DestroyMode:
 		v.view.streams.Println("Destroy cancelled.")
-	} else {
+	default:
 		v.view.streams.Println("Apply cancelled.")
 	}
 }

command/views/operation_test.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/hashicorp/terraform/command/arguments"
 	"github.com/hashicorp/terraform/internal/terminal"
+	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/states"
 	"github.com/hashicorp/terraform/states/statefile"
 )
@@ -24,16 +25,16 @@ func TestOperation_stopping(t *testing.T) {
 
 func TestOperation_cancelled(t *testing.T) {
 	testCases := map[string]struct {
-		destroy bool
+		planMode plans.Mode
-		want    string
+		want     string
 	}{
 		"apply": {
-			destroy: false,
+			planMode: plans.NormalMode,
-			want:    "Apply cancelled.\n",
+			want:     "Apply cancelled.\n",
 		},
 		"destroy": {
-			destroy: true,
+			planMode: plans.DestroyMode,
-			want:    "Destroy cancelled.\n",
+			want:     "Destroy cancelled.\n",
 		},
 	}
 	for name, tc := range testCases {
@@ -41,7 +42,7 @@ func TestOperation_cancelled(t *testing.T) {
 			streams, done := terminal.StreamsForTesting(t)
 			v := NewOperation(arguments.ViewHuman, false, NewView(streams))
 
-			v.Cancelled(tc.destroy)
+			v.Cancelled(tc.planMode)
 
 			if got, want := done(t).Stdout(), tc.want; got != want {
 				t.Errorf("wrong result\ngot:  %q\nwant: %q", got, want)