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site-lisp/blacken.el

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+;;; blacken.el --- Reformat python buffers using the "black" formatter
+
+;; Copyright (C) 2018 Artem Malyshev
+
+;; Author: Artem Malyshev <proofit404@gmail.com>
+;; Homepage: https://github.com/proofit404/blacken
+;; Version: 0.0.1
+;; Package-Requires: ((emacs "25.2"))
+
+;; This file is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published
+;; by the Free Software Foundation; either version 3, or (at your
+;; option) any later version.
+;;
+;; This file is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; For a full copy of the GNU General Public License
+;; see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; Blacken uses black to format a Python buffer.  It can be called
+;; explicitly on a certain buffer, but more conveniently, a minor-mode
+;; 'blacken-mode' is provided that turns on automatically running
+;; black on a buffer before saving.
+;;
+;; Installation:
+;;
+;; Add blacken.el to your load-path.
+;;
+;; To automatically format all Python buffers before saving, add the
+;; function blacken-mode to python-mode-hook:
+;;
+;; (add-hook 'python-mode-hook 'blacken-mode)
+;;
+;;; Code:
+
+
+(defgroup blacken nil
+  "Reformat Python code with \"black\"."
+  :group 'python)
+
+(defcustom blacken-executable "black"
+  "Name of the executable to run."
+  :type 'string)
+
+(defcustom blacken-line-length nil
+  "Line length to enforce."
+  :type 'number
+  :safe 'numberp)
+
+(defun blacken-call-bin (input-buffer output-buffer error-buffer)
+  "Call process black.
+
+Send INPUT-BUFFER content to the process stdin.  Saving the
+output to OUTPUT-BUFFER.  Saving process stderr to ERROR-BUFFER.
+Return black process the exit code."
+  (with-current-buffer input-buffer
+    (let ((process (make-process :name "blacken"
+                                 :command `(,blacken-executable ,@(blacken-call-args))
+                                 :buffer output-buffer
+                                 :stderr error-buffer
+                                 :noquery t
+                                 :sentinel (lambda (process event)))))
+      (set-process-query-on-exit-flag (get-buffer-process error-buffer) nil)
+      (set-process-sentinel (get-buffer-process error-buffer) (lambda (process event)))
+      (save-restriction
+        (widen)
+        (process-send-region process (point-min) (point-max)))
+      (process-send-eof process)
+      (accept-process-output process nil nil t)
+      (while (process-live-p process)
+        (accept-process-output process nil nil t))
+      (process-exit-status process))))
+
+(defun blacken-call-args ()
+  "Build black process call arguments."
+  (append
+   (when blacken-line-length
+     (list "--line-length" (number-to-string blacken-line-length)))
+   '("-")))
+
+;;;###autoload
+(defun blacken-buffer (&optional display)
+  "Try to blacken the current buffer.
+
+Show black output, if black exit abnormally and DISPLAY is t."
+  (interactive (list t))
+  (let* ((original-buffer (current-buffer))
+         (original-point (point))
+         (original-window-pos (window-start))
+         (tmpbuf (get-buffer-create "*blacken*"))
+         (errbuf (get-buffer-create "*blacken-error*")))
+    ;; This buffer can be left after previous black invocation.  It
+    ;; can contain error message of the previous run.
+    (dolist (buf (list tmpbuf errbuf))
+      (with-current-buffer buf
+        (erase-buffer)))
+    (condition-case err
+        (if (not (zerop (blacken-call-bin original-buffer tmpbuf errbuf)))
+            (error "Black failed, see %s buffer for details" (buffer-name errbuf))
+          (with-current-buffer tmpbuf
+            (copy-to-buffer original-buffer (point-min) (point-max)))
+          (mapc 'kill-buffer (list tmpbuf errbuf))
+          (goto-char original-point)
+          (set-window-start (selected-window) original-window-pos))
+      (error (message "%s" (error-message-string err))
+             (when display
+               (pop-to-buffer errbuf))))))
+
+;;;###autoload
+(define-minor-mode blacken-mode
+  "Automatically run black before saving."
+  :lighter " Black"
+  (if blacken-mode
+      (add-hook 'before-save-hook 'blacken-buffer nil t)
+    (remove-hook 'before-save-hook 'blacken-buffer t)))
+
+(provide 'blacken)
+
+;;; blacken.el ends here