Deprecate the tfmigrate plan --out=tfplan option

Closes #62

The tfmigrate plan --out=tfplan option was originally requested in #36,
and added in #37.

While testing Terraform 1.1 support, I found it no longer work with
Terraform 1.1. #62

After debugging, the tfmigrate plan --out=tfplan option was based on a
bug prior to Terraform 1.1.

Since terraform state push increments the serial of tfstate, a saved
plan file in tfmigrate plan phase should not be able to terraform apply.
However, prior to Terraform 1.1, there was no proper validation and
terraform apply allows a such case incorrectly. Starting from Terraform
1.1, it now rejects the plan as stale, which seems to be a correct
behavior.

That is, the tfmigrate plan --out=tfplan option doesn't work with
Terraform 1.1 or later. There is no way to do this.

Fortunately, Terraform 1.1 added a new `moved` block feature, so some
use-cases could be covered by the `moved` block.

So, I decided to deprecate the tfmigrate plan --out=tfplan option
without replacement and it will be removed in a future release.

command/plan.go

@@ -20,7 +20,7 @@ type PlanCommand struct {
 func (c *PlanCommand) Run(args []string) int {
 	cmdFlags := flag.NewFlagSet("plan", flag.ContinueOnError)
 	cmdFlags.StringVar(&c.configFile, "config", defaultConfigFile, "A path to tfmigrate config file")
-	cmdFlags.StringVar(&c.out, "out", "", "Save a plan file after dry-run migration to the given path")
+	cmdFlags.StringVar(&c.out, "out", "", "[Deprecated] Save a plan file after dry-run migration to the given path")
 
 	if err := cmdFlags.Parse(args); err != nil {
 		c.UI.Error(fmt.Sprintf("failed to parse arguments: %s", err))
@@ -40,6 +40,12 @@ func (c *PlanCommand) Run(args []string) int {
 	// So logging the option set log level to DEBUG instead of INFO.
 	log.Printf("[DEBUG] [command] option: %#v\n", c.Option)
 
+	// The tfmigrate plan --out=tfplan option is deprecated and doesn't work with Terraform 1.1+
+	// https://github.com/minamijoyo/tfmigrate/issues/62
+	if c.Option.PlanOut != "" {
+		log.Println("[WARN] The --out option is deprecated without replacement and it will be removed in a future release")
+	}
+
 	if c.config.History == nil {
 		// non-history mode
 		if len(cmdFlags.Args()) != 1 {
@@ -114,9 +120,13 @@ Arguments:
 
 Options:
   --config           A path to tfmigrate config file
-  --out=path         Save a plan file after dry-run migration to the given path.
+
+  [Deprecated]
+  --out=path
+                     Save a plan file after dry-run migration to the given path.
                      Note that applying the plan file only affects a local state,
                      make sure to force push it to remote after terraform apply.
+                     This option doesn't work with Terraform 1.1+
 `
 	return strings.TrimSpace(helpText)
 }

tfmigrate/multi_state_migrator_test.go

@@ -326,6 +326,23 @@ func TestAccMultiStateMigratorApply(t *testing.T) {
 			}
 
 			if tc.force {
+				// The tfmigrate plan --out=tfplan option is deprecated and doesn't work with Terraform 1.1+
+				// https://github.com/minamijoyo/tfmigrate/issues/62
+				fromTfVersionMatched, err := tfexec.MatchTerraformVersion(ctx, fromTf, ">= 1.1.0")
+				if err != nil {
+					t.Fatalf("failed to check terraform version constraints in fromDir: %s", err)
+				}
+				if fromTfVersionMatched {
+					t.Skip("skip the following test because the saved plan can't apply in Terraform v1.1+")
+				}
+				toTfVersionMatched, err := tfexec.MatchTerraformVersion(ctx, toTf, ">= 1.1.0")
+				if err != nil {
+					t.Fatalf("failed to check terraform version constraints in toDir: %s", err)
+				}
+				if toTfVersionMatched {
+					t.Skip("skip the following test because the saved plan can't apply in Terraform v1.1+")
+				}
+
 				// apply the saved plan files
 				fromPlan, err := ioutil.ReadFile(filepath.Join(fromTf.Dir(), o.PlanOut))
 				if err != nil {
@@ -346,14 +363,14 @@ func TestAccMultiStateMigratorApply(t *testing.T) {
 
 				// Terraform >= v0.12.25 and < v0.13 has a bug for state push -force
 				// https://github.com/hashicorp/terraform/issues/25761
-				fromTfVersionMatched, err := tfexec.MatchTerraformVersion(ctx, fromTf, ">= 0.12.25, < 0.13")
+				fromTfVersionMatched, err = tfexec.MatchTerraformVersion(ctx, fromTf, ">= 0.12.25, < 0.13")
 				if err != nil {
 					t.Fatalf("failed to check terraform version constraints in fromDir: %s", err)
 				}
 				if fromTfVersionMatched {
 					t.Skip("skip the following test due to a bug in Terraform v0.12")
 				}
-				toTfVersionMatched, err := tfexec.MatchTerraformVersion(ctx, toTf, ">= 0.12.25, < 0.13")
+				toTfVersionMatched, err = tfexec.MatchTerraformVersion(ctx, toTf, ">= 0.12.25, < 0.13")
 				if err != nil {
 					t.Fatalf("failed to check terraform version constraints in toDir: %s", err)
 				}

tfmigrate/state_migrator_test.go

@@ -288,6 +288,18 @@ resource "aws_security_group" "baz" {}
 		t.Fatalf("expect to have changes")
 	}
 
+	// The tfmigrate plan --out=tfplan option was based on a bug prior to Terraform 1.1.
+	// Terraform v1.1 now rejects the plan as stale.
+	// The tfmigrate plan --out=tfplan option is deprecated without replacement.
+	// https://github.com/minamijoyo/tfmigrate/issues/62
+	tfVersionMatched, err := tfexec.MatchTerraformVersion(ctx, tf, ">= 1.1.0")
+	if err != nil {
+		t.Fatalf("failed to check terraform version constraints: %s", err)
+	}
+	if tfVersionMatched {
+		t.Skip("skip the following test because the saved plan can't apply in Terraform v1.1+")
+	}
+
 	// apply the saved plan files
 	plan, err := ioutil.ReadFile(filepath.Join(tf.Dir(), o.PlanOut))
 	if err != nil {
@@ -300,7 +312,7 @@ resource "aws_security_group" "baz" {}
 
 	// Terraform >= v0.12.25 and < v0.13 has a bug for state push -force
 	// https://github.com/hashicorp/terraform/issues/25761
-	tfVersionMatched, err := tfexec.MatchTerraformVersion(ctx, tf, ">= 0.12.25, < 0.13")
+	tfVersionMatched, err = tfexec.MatchTerraformVersion(ctx, tf, ">= 0.12.25, < 0.13")
 	if err != nil {
 		t.Fatalf("failed to check terraform version constraints: %s", err)
 	}