Introduce S3-native state locking

internal/backend/remote-state/s3/backend.go

@@ -46,6 +46,7 @@ type Backend struct {
 	acl                   string
 	kmsKeyID              string
 	ddbTable              string
+	useLockFile           bool
 	workspaceKeyPrefix    string
 	skipS3Checksum        bool
 }
@@ -152,6 +153,11 @@ func (b *Backend) ConfigSchema() *configschema.Block {
 				Optional:    true,
 				Description: "DynamoDB table for state locking and consistency",
 			},
+			"use_lockfile": {
+				Type:        cty.Bool,
+				Optional:    true,
+				Description: "(Experimental) Whether to use a lockfile for locking the state file.",
+			},
 			"profile": {
 				Type:        cty.String,
 				Optional:    true,
@@ -822,6 +828,7 @@ func (b *Backend) Configure(obj cty.Value) tfdiags.Diagnostics {
 	b.serverSideEncryption = boolAttr(obj, "encrypt")
 	b.kmsKeyID = stringAttr(obj, "kms_key_id")
 	b.ddbTable = stringAttr(obj, "dynamodb_table")
+	b.useLockFile = boolAttr(obj, "use_lockfile")
 	b.skipS3Checksum = boolAttr(obj, "skip_s3_checksum")
 
 	if _, ok := stringAttrOk(obj, "kms_key_id"); ok {

internal/backend/remote-state/s3/backend_state.go

@@ -27,6 +27,8 @@ const (
 	// defaultWorkspaceKeyPrefix is the default prefix for workspace storage.
 	// The colon is used to reduce the chance of name conflicts with existing objects.
 	defaultWorkspaceKeyPrefix = "env:"
+	// lockFileSuffix defines the suffix for Terraform state lock files.
+	lockFileSuffix = ".tflock"
 )
 
 func (b *Backend) Workspaces() ([]string, error) {
@@ -163,6 +165,8 @@ func (b *Backend) remoteClient(name string) (*RemoteClient, error) {
 		kmsKeyID:              b.kmsKeyID,
 		ddbTable:              b.ddbTable,
 		skipS3Checksum:        b.skipS3Checksum,
+		lockFilePath:          b.getLockFilePath(name),
+		useLockFile:           b.useLockFile,
 	}
 
 	return client, nil
@@ -276,3 +280,9 @@ func newBucketRegionError(requestRegion, bucketRegion string) bucketRegionError
 func (err bucketRegionError) Error() string {
 	return fmt.Sprintf("requested bucket from %q, actual location %q", err.requestRegion, err.bucketRegion)
 }
+
+// getLockFilePath returns the path to the lock file for the given Terraform state.
+// For `default.tfstate`, the lock file is stored at `default.tfstate.tflock`.
+func (b *Backend) getLockFilePath(name string) string {
+	return b.path(name) + lockFileSuffix
+}