terragrunt configurations sometimes have no tf files, but do have ter…

…raform lockfiles

lib/modules/manager/terragrunt/index.ts

@@ -2,6 +2,7 @@ import { GitTagsDatasource } from '../../datasource/git-tags';
 import { GithubTagsDatasource } from '../../datasource/github-tags';
 import { TerraformModuleDatasource } from '../../datasource/terraform-module';
 
+export { updateArtifacts } from './lockfile';
 export { extractPackageFile } from './extract';
 
 export const supportedDatasources = [
@@ -10,6 +11,7 @@ export const supportedDatasources = [
   TerraformModuleDatasource.id,
 ];
 
+export const supportsLockFileMaintenance = true;
 export const defaultConfig = {
   commitMessageTopic: 'Terragrunt dependency {{depName}}',
   fileMatch: ['(^|/)terragrunt\\.hcl$'],

lib/modules/manager/terragrunt/lockfile.ts

@@ -0,0 +1,12 @@
+import { updateArtifacts as updateTerraformArtifacts } from '../terraform/lockfile/index';
+import type { UpdateArtifact, UpdateArtifactsResult } from '../types';
+
+export async function updateArtifacts(
+  artifact: UpdateArtifact
+): Promise<UpdateArtifactsResult[] | null> {
+  if (artifact.config.updateType !== 'lockFileMaintenance') {
+    return null;
+  }
+
+  return await updateTerraformArtifacts(artifact);
+}