add args support for typescript plugin

plugins/plugin-typescript/README.md

@@ -19,3 +19,9 @@ module.exports = {
   plugins: ['@snowpack/plugin-typescript'],
 };
 ```
+
+## Plugin Options
+
+| Name   |   Type   | Description                                                                                                                                                                      |
+| :----- | :------: | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `args` | `string` | Optional arguments to pass to the `tsc` CLI. For example, you can configure a custom project directory (with a custom `tsconfig.json` file) using `args: "--project ./your/custom/path"`. |

plugins/plugin-typescript/plugin.js

@@ -2,11 +2,11 @@ const execa = require('execa');
 const npmRunPath = require('npm-run-path');
 const cwd = process.cwd();
 
-function typescriptPlugin() {
+function typescriptPlugin(_, {args} = {}) {
   return {
     name: '@snowpack/plugin-typescript',
     async run({isDev, log}) {
-      const workerPromise = execa.command(`tsc --noEmit ${isDev ? '--watch' : ''}`, {
+      const workerPromise = execa.command(`tsc --noEmit ${isDev ? '--watch' : ''} ${args ? args : ''}`, {
         env: npmRunPath.env(),
         extendEnv: true,
         windowsHide: false,

plugins/plugin-typescript/test/plugin.test.js

@@ -31,6 +31,11 @@ describe('plugin-typescript', () => {
     expect(execaFn.mock.calls[0][0]).toContain('--noEmit');
     expect(execaFn.mock.calls[0][0]).toContain('--watch');
   });
+  test('calls "tsc" correctly with args', async () => {
+    const p = plugin(undefined, {args: '--foo bar'});
+    await p.run({isDev: false, log: jest.fn});
+    expect(execaFn.mock.calls[0][0]).toContain('--foo bar');
+  });
   test('handles tsc output', async () => {
     const logFn = jest.fn();
     const p = plugin();