add core infrastructure for 'add' command

- Create additions registry for managing optional feature additions
- Implement additions manager with runAddition, executeAddition
- Add utilities that reuse migration infrastructure (Context, formatFiles, etc.)
- Support for version-agnostic, idempotent additions
- Designed to be extensible for future additions beyond i18n

     Fri Oct 17 09:48:24 2025 +0200
add core infrastructure for 'add' command
implement 'add' command with pre-flight checks
implement 'add i18n' script with full automation
  packages/create-plugin/src/additions/additions.ts
  packages/create-plugin/src/additions/manager.ts
  packages/create-plugin/src/additions/utils.ts

Author: sunker

packages/create-plugin/src/additions/additions.ts

@@ -0,0 +1,19 @@
+export type AdditionMeta = {
+  name: string;
+  description: string;
+  scriptPath: string;
+};
+
+type Additions = {
+  additions: Record<string, AdditionMeta>;
+};
+
+export default {
+  additions: {
+    i18n: {
+      name: 'i18n',
+      description: 'Add internationalization (i18n) support to your plugin',
+      scriptPath: './scripts/add-i18n.js',
+    },
+  },
+} as Additions;

packages/create-plugin/src/additions/manager.ts

@@ -0,0 +1,77 @@
+import { additionsDebug, flushChanges, formatFiles, installNPMDependencies, printChanges } from './utils.js';
+import defaultAdditions, { AdditionMeta } from './additions.js';
+
+import { Context } from '../migrations/context.js';
+import { gitCommitNoVerify } from '../utils/utils.git.js';
+import { output } from '../utils/utils.console.js';
+
+export type AdditionFn = (context: Context, options?: AdditionOptions) => Context | Promise<Context>;
+
+export type AdditionOptions = Record<string, any>;
+
+type RunAdditionOptions = {
+  commitChanges?: boolean;
+};
+
+export function getAvailableAdditions(
+  additions: Record<string, AdditionMeta> = defaultAdditions.additions
+): Record<string, AdditionMeta> {
+  return additions;
+}
+
+export function getAdditionByName(
+  name: string,
+  additions: Record<string, AdditionMeta> = defaultAdditions.additions
+): AdditionMeta | undefined {
+  return additions[name];
+}
+
+export async function runAddition(
+  addition: AdditionMeta,
+  additionOptions: AdditionOptions = {},
+  runOptions: RunAdditionOptions = {}
+): Promise<void> {
+  const basePath = process.cwd();
+
+  output.log({
+    title: `Running addition: ${addition.name}`,
+    body: [addition.description],
+  });
+
+  try {
+    const context = new Context(basePath);
+    const updatedContext = await executeAddition(addition, context, additionOptions);
+    const shouldCommit = runOptions.commitChanges && updatedContext.hasChanges();
+
+    additionsDebug(`context for "${addition.name} (${addition.scriptPath})":`);
+    additionsDebug('%O', updatedContext.listChanges());
+
+    await formatFiles(updatedContext);
+    flushChanges(updatedContext);
+    printChanges(updatedContext, addition.name, addition);
+
+    installNPMDependencies(updatedContext);
+
+    if (shouldCommit) {
+      await gitCommitNoVerify(`chore: add ${addition.name} support via create-plugin`);
+    }
+
+    output.success({
+      title: `Successfully added ${addition.name} to your plugin.`,
+    });
+  } catch (error) {
+    if (error instanceof Error) {
+      throw new Error(`Error running addition "${addition.name} (${addition.scriptPath})": ${error.message}`);
+    }
+    throw error;
+  }
+}
+
+export async function executeAddition(
+  addition: AdditionMeta,
+  context: Context,
+  options: AdditionOptions = {}
+): Promise<Context> {
+  const module: { default: AdditionFn } = await import(addition.scriptPath);
+  return module.default(context, options);
+}

packages/create-plugin/src/additions/utils.ts

@@ -0,0 +1,39 @@
+export {
+  formatFiles,
+  installNPMDependencies,
+  flushChanges,
+  addDependenciesToPackageJson,
+} from '../migrations/utils.js';
+
+import type { AdditionMeta } from './additions.js';
+import { Context } from '../migrations/context.js';
+import chalk from 'chalk';
+// Re-export debug with additions namespace
+import { debug } from '../utils/utils.cli.js';
+import { output } from '../utils/utils.console.js';
+
+export const additionsDebug = debug.extend('additions');
+
+export function printChanges(context: Context, key: string, addition: AdditionMeta) {
+  const changes = context.listChanges();
+  const lines = [];
+
+  for (const [filePath, { changeType }] of Object.entries(changes)) {
+    if (changeType === 'add') {
+      lines.push(`${chalk.green('ADD')} ${filePath}`);
+    } else if (changeType === 'update') {
+      lines.push(`${chalk.yellow('UPDATE')} ${filePath}`);
+    } else if (changeType === 'delete') {
+      lines.push(`${chalk.red('DELETE')} ${filePath}`);
+    }
+  }
+
+  output.addHorizontalLine('gray');
+  output.logSingleLine(`${key} (${addition.description})`);
+
+  if (lines.length === 0) {
+    output.logSingleLine('No changes were made');
+  } else {
+    output.log({ title: 'Changes:', withPrefix: false, body: output.bulletList(lines) });
+  }
+}