editor/format: add +format-with option

+ A formatter can now be specified explicitly buffer-locally by setting
  +format-with to a symbol representing the name of the
  formatter (accepts any key of format-all-format-table)
+ Passing C-u to any of +format/buffer, +format/region or
  +format/region-or-buffer will now prompt you to select a formatter.
+ Revise docstring for +format-on-save-enabled-modes

modules/editor/format/autoload/format.el

@@ -86,7 +86,19 @@ Stolen shamelessly from go-mode"
 
 ;;
 ;; Public library
-;;
+
+(defun +format-completing-read ()
+  (require 'format-all)
+  (let* ((fmtlist (mapcar #'symbol-name (hash-table-keys format-all-format-table)))
+         (fmt (completing-read "Formatter: " fmtlist)))
+    (if fmt (cons (intern fmt) t))))
+
+;;;###autoload
+(defun +format*probe (orig-fn)
+  "Use `+format-with' instead, if it is set."
+  (if +format-with
+      (cons +format-with t)
+    (funcall orig-fn)))
 
 ;;;###autoload
 (defun +format-buffer (formatter mode-result)
@@ -156,31 +168,32 @@ See `+format/buffer' for the interactive version of this function, and
 ;; Commands
 
 ;;;###autoload
-(defun +format/buffer ()
+(defun +format/buffer (&optional arg)
   "Format the source code in the current buffer."
-  (interactive)
-  (+format|buffer))
+  (interactive "P")
+  (let ((+format-with (if arg (+format-completing-read))))
+    (+format|buffer arg)))
 
 ;;;###autoload
-(defun +format/region (beg end)
+(defun +format/region (beg end &optional arg)
   "Runs the active formatter on the lines within BEG and END.
 
 WARNING: this may not work everywhere. It will throw errors if the region
 contains a syntax error in isolation. It is mostly useful for formatting
 snippets or single lines."
-  (interactive "r")
+  (interactive "rP")
   (save-restriction
     (narrow-to-region beg end)
-    (+format/buffer)))
+    (+format/buffer arg)))
 
 ;;;###autoload
-(defun +format/region-or-buffer (beg end)
+(defun +format/region-or-buffer (beg end &optional arg)
   "Runs the active formatter on the selected region (or whole buffer, if nothing
 is selected)."
-  (interactive "r")
+  (interactive "rP")
   (if (use-region-p)
-      (+format/region beg end)
-    (+format/buffer)))
+      (+format/region beg end arg)
+    (+format/buffer arg)))
 
 
 ;;

modules/editor/format/config.el

@@ -3,14 +3,17 @@
 (defvar +format-on-save-enabled-modes
   '(not emacs-lisp-mode  ; elisp's mechanisms are good enough
         sql-mode)        ; sqlformat is currently broken
-  "A list of major modes in which to enable `format-all-mode'.
-
-This mode will auto-format buffers when you save them.
+  "A list of major modes in which to reformat the buffer upon saving.
 
 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.")
+  used at all.
+
+Irrelevant if you do not have the +onsave flag enabled for this module.")
+
+(defvar-local +format-with nil "Set this to explicitly use a certain formatter
+  for the current buffer.")
 
 
 ;;
@@ -32,3 +35,11 @@ This is controlled by `+format-on-save-enabled-modes'."
 
 (when (featurep! +onsave)
   (add-hook 'after-change-major-mode-hook #'+format|enable-on-save-maybe))
+
+
+;;
+;; Hacks
+
+;; Allow a specific formatter to be used by setting `+format-with', either
+;; buffer-locally or let-bound.
+(advice-add #'format-all-probe :around #'+format*probe)