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 {
-	case op.Destroy:
-		opts.PlanMode = plans.DestroyMode
-	default:
-		opts.PlanMode = plans.NormalMode
-	}
+	opts.PlanMode = op.PlanMode
 	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 {
-	case op.Destroy:
-		opts.PlanMode = plans.DestroyMode
-	default:
-		opts.PlanMode = plans.NormalMode
-	}
+	opts.PlanMode = op.PlanMode
 	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)