New :editor format module

Centralized code formatting with built-in support for a variety of
languages. Provides the set-formatter! function for defining your own.

Still experimental and needs more testing!

modules/editor/format/config.el

@@ -0,0 +1,32 @@
+;;; editor/format/config.el -*- lexical-binding: t; -*-
+
+(defvar +format-on-save-enabled-modes t
+  "A list of major modes in which to enable `format-all-mode'.
+
+This mode will auto-format buffers when you save them.
+
+If this list begins with `not', then it negates the list.
+If it is `t', it is enabled in all modes.
+If nil, it is disabled in all modes, the same as if the +onsave flag wasn't
+  used at all.")
+
+
+;;
+;; Plugins
+;;
+
+(defun +format|enable-on-save-maybe ()
+  "Enable `format-all-mode' in buffers. See `+format-on-save-enabled-modes' to
+control which major modes to target."
+  (unless (or (eq major-mode 'fundamental-mode)
+              (cond ((booleanp +format-on-save-enabled-modes)
+                     (null +format-on-save-enabled-modes))
+                    ((eq (car +format-on-save-enabled-modes) 'not)
+                     (memq major-mode (cdr +format-on-save-enabled-modes)))
+                    ((not (memq major-mode +format-on-save-enabled-modes))))
+              (require 'format-all nil t)
+              (not (format-all-probe)))
+    (format-all-mode +1)))
+
+(when (featurep! +onsave)
+  (add-hook 'after-change-major-mode-hook #'+format|enable-on-save-maybe))