feat(emacs): support TypeScript in Flymake plugin

Use --language=experimental-default in the Flymake plugin so
quick-lint-js parses .ts files as TypeScript files. To make this work
with --stdin, use --stdin-path as well.

docs/CHANGELOG.md

@@ -29,6 +29,8 @@ Semantic Versioning.
 * TypeScript support (still experimental):
   * CLI: The new `--language=experimental-default` option auto-detects the
     language based on the file's extension (`.ts`, `.tsx`, `.d.ts`, or `.js`).
+  * Emacs: Flymake plugin users can now opt into TypeScript support. See the
+    [Flymake configuration instructions][emacs-configure-flymake].
   * Class method overload signatures are now parsed.
   * [E0398][] is now reported when using both `abstract` and `static` on a
     single class property.
@@ -1066,6 +1068,7 @@ Beta release.
 [coc.nvim]: https://github.com/neoclide/coc.nvim
 [config-global-groups]: https://quick-lint-js.com/config/#global-groups
 [cross-compiling-quick-lint-js]: https://quick-lint-js.com/contribute/build-from-source/cross-compiling/
+[emacs-configure-flymake]: https://quick-lint-js.com/install/emacs/configure/#flymake
 [install-powershell-completions]: https://github.com/quick-lint/quick-lint-js/blob/master/completions/README.md#powershell
 
 [AidenThing]: https://github.com/AidenThing

plugin/emacs/flymake-quicklintjs.el

@@ -39,6 +39,11 @@
   :group 'flymake-quicklintjs
   :type '(repeat string))
 
+(defcustom flymake-quicklintjs-experimental-typescript nil
+  "Enable experimental TypeScript support (EXPERIMENTAL; subject to change in future versions of quick-lint-js)."
+  :group 'flymake-quicklintjs
+  :type '(boolean))
+
 (defvar-local flymake-quicklintjs--proc nil
   "Internal variable for `flymake-quicklintjs'")
 
@@ -74,8 +79,11 @@ REPORT-FN is Flymake's callback."
            :command `(,flymake-quicklintjs-program
                       ,@(let ((file (buffer-file-name)))
                           (if file
-                            `("--path-for-config-search" ,file)
+                            `("--stdin-path" ,file)
                             ()))
+                      ,@(if flymake-quicklintjs-experimental-typescript
+                            `("--language=experimental-default")
+                          ())
                       "--stdin" "--output-format=emacs-lisp"
                       ,@flymake-quicklintjs-args)
            :sentinel

website/public/install/emacs/configure/index.ejs.html

@@ -121,7 +121,15 @@ <h2 id="flymake">Flymake</h2>
   ;; Optional: Remove the time to wait after last change before automatically
   ;; checking buffer. The default is 0.5 (500ms)
   (setq-local flymake-no-changes-timeout 0))
-(add-hook 'js-mode-hook #'my-flymake-quicklintjs-setup)</code></pre>
+(add-hook 'js-mode-hook #'my-flymake-quicklintjs-setup)
+
+;; Optional: Enable TypeScript support. Requires quick-lint-js version
+;; 2.17.0 or newer.
+;; EXPERIMENTAL. Subject to change in future versions of
+;; quick-lint-js.
+(add-hook 'typescript-mode-hook #'my-flymake-quicklintjs-setup)
+(setq flymake-quicklintjs-experimental-typescript t)
+</code></pre>
 
       <h2 id="lsp-mode">LSP Mode</h2>
       <p>