fix purcell#25 hook for post-processing formatter output

reformatter.el

@@ -75,7 +75,7 @@
 (require 'ansi-color)
 
 ;;;###autoload
-(cl-defmacro reformatter-define (name &key program args (mode t) lighter keymap group (exit-code-success-p 'zerop))
+(cl-defmacro reformatter-define (name &key program args (mode t) lighter keymap group (exit-code-success-p 'zerop) (output-post-processor 'identity))
   "Define a reformatter command with NAME.
 
 When called, the reformatter will use PROGRAM and any ARGS to
@@ -129,10 +129,17 @@ The macro accepts the following keyword arguments:
   which accepts an integer process exit code, and returns non-nil
   if that exit code is considered successful.  This could be a
   lambda, quoted symbol or sharp-quoted symbol.  If not supplied,
-  the code is considered successful if it is `zerop'."
+  the code is considered successful if it is `zerop'.
+
+:output-post-processor
+
+  If provided, this is a function that takes the output PROGRAM,
+  do some arbitrary processing to it, and then return the final
+  output.  If not supplied, the output is returned as is."
   (declare (indent defun))
   (cl-assert (symbolp name))
   (cl-assert (functionp exit-code-success-p))
+  (cl-assert (functionp output-post-processor))
   (cl-assert program)
   ;; Note: we skip using `gensym' here because the macro arguments are only
   ;; referred to once below, but this may have to change later.
@@ -198,7 +205,7 @@ DISPLAY-ERRORS, shows a buffer if the formatting fails."
                          ;; disruption to marker positions and the
                          ;; undo list
                          (narrow-to-region beg end)
-                         (reformatter-replace-buffer-contents-from-file out-file))
+                         (reformatter-replace-buffer-contents-from-file (funcall ,output-post-processor out-file)))
                          ;; if there is no errors the error-buffer shouldn't be kept open
                        (delete-windows-on error-buffer))
                    (if display-errors