Use precomputed terraform plan for bundle deploy (#1640)

# Changes
With #1413 we started to compute
and partially print the plan if it contained deletion of UC schemas.
This PR uses the precomputed plan to avoid double planning when actually
doing the terraform plan.

This fixes a performance regression introduced in
#1413.

# Tests

Tested manually.
1. Verified bundle deployment still works and deploys resources.
2. Verified that the precomputed plan is indeed being used by attaching
a debugger and removing the plan file right before the terraform apply
process is spawned and asserting that terraform apply fails because the
plan is not found.

bundle/deploy/terraform/apply.go

@@ -4,7 +4,6 @@ import (
 	"context"
 
 	"github.com/databricks/cli/bundle"
-	"github.com/databricks/cli/libs/cmdio"
 	"github.com/databricks/cli/libs/diag"
 	"github.com/databricks/cli/libs/log"
 	"github.com/hashicorp/terraform-exec/tfexec"
@@ -17,28 +16,32 @@ func (w *apply) Name() string {
 }
 
 func (w *apply) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagnostics {
+	// return early if plan is empty
+	if b.Plan.IsEmpty {
+		log.Debugf(ctx, "No changes in plan. Skipping terraform apply.")
+		return nil
+	}
+
 	tf := b.Terraform
 	if tf == nil {
 		return diag.Errorf("terraform not initialized")
 	}
 
-	cmdio.LogString(ctx, "Deploying resources...")
-
-	err := tf.Init(ctx, tfexec.Upgrade(true))
-	if err != nil {
-		return diag.Errorf("terraform init: %v", err)
+	if b.Plan.Path == "" {
+		return diag.Errorf("no plan found")
 	}
 
-	err = tf.Apply(ctx)
+	// Apply terraform according to the computed plan
+	err := tf.Apply(ctx, tfexec.DirOrPlan(b.Plan.Path))
 	if err != nil {
 		return diag.Errorf("terraform apply: %v", err)
 	}
 
-	log.Infof(ctx, "Resource deployment completed")
+	log.Infof(ctx, "terraform apply completed")
 	return nil
 }
 
-// Apply returns a [bundle.Mutator] that runs the equivalent of `terraform apply`
+// Apply returns a [bundle.Mutator] that runs the equivalent of `terraform apply ./plan`
 // from the bundle's ephemeral working directory for Terraform.
 func Apply() bundle.Mutator {
 	return &apply{}

bundle/deploy/terraform/state_push.go

@@ -2,6 +2,8 @@ package terraform
 
 import (
 	"context"
+	"errors"
+	"io/fs"
 	"os"
 	"path/filepath"
 
@@ -34,6 +36,12 @@ func (l *statePush) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagnostic
 
 	// Expect the state file to live under dir.
 	local, err := os.Open(filepath.Join(dir, TerraformStateFileName))
+	if errors.Is(err, fs.ErrNotExist) {
+		// The state file can be absent if terraform apply is skipped because
+		// there are no changes to apply in the plan.
+		log.Debugf(ctx, "Local terraform state file does not exist.")
+		return nil
+	}
 	if err != nil {
 		return diag.FromErr(err)
 	}

bundle/phases/deploy.go

@@ -92,7 +92,10 @@ func Deploy() bundle.Mutator {
 	// Core mutators that CRUD resources and modify deployment state. These
 	// mutators need informed consent if they are potentially destructive.
 	deployCore := bundle.Defer(
-		terraform.Apply(),
+		bundle.Seq(
+			bundle.LogString("Deploying resources..."),
+			terraform.Apply(),
+		),
 		bundle.Seq(
 			terraform.StatePush(),
 			terraform.Load(),

bundle/phases/destroy.go

@@ -82,7 +82,7 @@ func approvalForDestroy(ctx context.Context, b *bundle.Bundle) (bool, error) {
 func Destroy() bundle.Mutator {
 	// Core destructive mutators for destroy. These require informed user consent.
 	destroyCore := bundle.Seq(
-		terraform.Destroy(),
+		terraform.Apply(),
 		terraform.StatePush(),
 		files.Delete(),
 		bundle.LogString("Destroy complete!"),