add skip_plan option to state migrator

This addresses issue #151 to add a `skip_plan` option to single state
migrations, similar to the `from_skip_plan` and `to_skip_plan` options
supported by multi state migrations.

tfmigrate/state_import_action_test.go

@@ -40,7 +40,7 @@ resource "time_static" "baz" { triggers = {} }
 		NewStateImportAction("time_static.baz", "2006-01-02T15:04:05Z"),
 	}
 
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)

tfmigrate/state_migrator.go

@@ -28,6 +28,8 @@ type StateMigratorConfig struct {
 	// Force option controls behaviour in case of unexpected diff in plan.
 	// When set forces applying even if plan shows diff.
 	Force bool `hcl:"force,optional"`
+	// SkipPlan controls whether or not to run and analyze Terraform plan.
+	SkipPlan bool `hcl:"to_skip_plan,optional"`
 	// Workspace is the state workspace which the migration works with.
 	Workspace string `hcl:"workspace,optional"`
 }
@@ -62,7 +64,7 @@ func (c *StateMigratorConfig) NewMigrator(o *MigratorOption) (Migrator, error) {
 		c.Workspace = "default"
 	}
 
-	return NewStateMigrator(dir, c.Workspace, actions, o, c.Force), nil
+	return NewStateMigrator(dir, c.Workspace, actions, o, c.Force, c.SkipPlan), nil
 }
 
 // StateMigrator implements the Migrator interface.
@@ -74,6 +76,8 @@ type StateMigrator struct {
 	// o is an option for migrator.
 	// It is used for shared settings across Migrator instances.
 	o *MigratorOption
+	// skipPlan controls whether or not to run and analyze Terraform plan.
+	skipPlan bool
 	// force operation in case of unexpected diff
 	force bool
 	// workspace is the state workspace which the migration works with.
@@ -84,7 +88,7 @@ var _ Migrator = (*StateMigrator)(nil)
 
 // NewStateMigrator returns a new StateMigrator instance.
 func NewStateMigrator(dir string, workspace string, actions []StateAction,
-	o *MigratorOption, force bool) *StateMigrator {
+	o *MigratorOption, force bool, skipPlan bool) *StateMigrator {
 	e := tfexec.NewExecutor(dir, os.Environ())
 	tf := tfexec.NewTerraformCLI(e)
 	if o != nil && len(o.ExecPath) > 0 {
@@ -96,6 +100,7 @@ func NewStateMigrator(dir string, workspace string, actions []StateAction,
 		actions:   actions,
 		o:         o,
 		force:     force,
+		skipPlan:  skipPlan,
 		workspace: workspace,
 	}
 }
@@ -145,19 +150,23 @@ func (m *StateMigrator) plan(ctx context.Context) (currentState *tfexec.State, e
 		planOpts = append(planOpts, "-out="+m.o.PlanOut)
 	}
 
-	log.Printf("[INFO] [migrator@%s] check diffs\n", m.tf.Dir())
-	_, err = m.tf.Plan(ctx, currentState, planOpts...)
-	if err != nil {
-		if exitErr, ok := err.(tfexec.ExitError); ok && exitErr.ExitCode() == 2 {
-			if !m.force {
-				log.Printf("[ERROR] [migrator@%s] unexpected diffs\n", m.tf.Dir())
-				return nil, fmt.Errorf("terraform plan command returns unexpected diffs: %s", err)
+	if m.skipPlan {
+		log.Printf("[INFO] [migrator@%s] skipping check diffs\n", m.tf.Dir())
+	} else {
+		log.Printf("[INFO] [migrator@%s] check diffs\n", m.tf.Dir())
+		_, err = m.tf.Plan(ctx, currentState, planOpts...)
+		if err != nil {
+			if exitErr, ok := err.(tfexec.ExitError); ok && exitErr.ExitCode() == 2 {
+				if !m.force {
+					log.Printf("[ERROR] [migrator@%s] unexpected diffs\n", m.tf.Dir())
+					return nil, fmt.Errorf("terraform plan command returns unexpected diffs: %s", err)
+				}
+				log.Printf("[INFO] [migrator@%s] unexpected diffs, ignoring as force option is true: %s", m.tf.Dir(), err)
+				// reset err to nil to intentionally ignore unexpected diffs.
+				err = nil
+			} else {
+				return nil, err
 			}
-			log.Printf("[INFO] [migrator@%s] unexpected diffs, ignoring as force option is true: %s", m.tf.Dir(), err)
-			// reset err to nil to intentionally ignore unexpected diffs.
-			err = nil
-		} else {
-			return nil, err
 		}
 	}
 

tfmigrate/state_migrator_test.go

@@ -166,7 +166,7 @@ resource "time_static" "qux" { triggers = {} }
 	}
 
 	force := false
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)
@@ -236,7 +236,7 @@ resource "null_resource" "bar" {}
 	}
 
 	force := false
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)
@@ -308,7 +308,7 @@ resource "null_resource" "baz" {}
 	o := &MigratorOption{}
 	o.PlanOut = "foo.tfplan"
 	force := true
-	m := NewStateMigrator(tf.Dir(), workspace, actions, o, force)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, o, force, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)
@@ -440,7 +440,7 @@ resource "null_resource" "bar" {}
 	}
 
 	force := false
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force, false)
 
 	err := m.Plan(ctx)
 	if err == nil {
@@ -479,7 +479,7 @@ resource "null_resource" "bar" {}
 	}
 
 	force := false
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force, false)
 
 	err := m.Plan(ctx)
 	if err == nil {
@@ -524,7 +524,7 @@ resource "null_resource" "bar" {}
 	}
 
 	force := false
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, force, false)
 
 	err := m.Plan(ctx)
 	if err == nil {

tfmigrate/state_mv_action_test.go

@@ -43,7 +43,7 @@ resource "null_resource" "baz" {}
 		NewStateMvAction("null_resource.bar", "null_resource.bar2"),
 	}
 
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)

tfmigrate/state_replace_provider_action_test.go

@@ -36,7 +36,7 @@ resource "null_resource" "foo" {}
 	}
 
 	expected := "replace-provider action requires Terraform version >= 0.13.0"
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false, false)
 	err := m.Plan(ctx)
 	if err == nil || strings.Contains(err.Error(), expected) {
 		t.Fatalf("expected to receive '%s' error using legacy Terraform; got: %s", expected, err)
@@ -96,7 +96,7 @@ func TestAccStateReplaceProviderAction(t *testing.T) {
 		NewStateReplaceProviderAction("registry.terraform.io/-/null", "registry.terraform.io/hashicorp/null"),
 	}
 
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)

tfmigrate/state_rm_action_test.go

@@ -42,7 +42,7 @@ resource "null_resource" "baz" {}
 		NewStateRmAction([]string{"null_resource.qux"}),
 	}
 
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)

tfmigrate/state_xmv_action_test.go

@@ -39,7 +39,7 @@ resource "null_resource" "bar2" {}
 		NewStateXmvAction("null_resource.*", "null_resource.${1}2"),
 	}
 
-	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false)
+	m := NewStateMigrator(tf.Dir(), workspace, actions, &MigratorOption{}, false, false)
 	err = m.Plan(ctx)
 	if err != nil {
 		t.Fatalf("failed to run migrator plan: %s", err)