From 84a4dd4ef7a6ae9e49cb7442070744b5d6e3ec95 Mon Sep 17 00:00:00 2001
From: Lele Gaifax <lele@metapensiero.it>
Date: Fri, 13 Oct 2017 10:44:02 +0200
Subject: [PATCH 2/2] Add a Flymake backend for Python

* lisp/progmodes/python.el: Implement new Flymake backend with
  related customizable settings.
  (python-flymake-command, python-flymake-command-output-regexp,
   python-flymake-msg-alist): New defcustom.
  (python-flymake): New function.
  (python-flymake-activate): New function.
---
 lisp/progmodes/python.el | 101 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index f79d9a47d3..866e02ffbd 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -5141,6 +5141,107 @@ python-util-valid-regexp-p
   (ignore-errors (string-match regexp "") t))
 
 
+;;; Flymake integration
+
+(defgroup python-flymake nil
+  "Integration between Python and Flymake."
+  :group 'python
+  :link '(custom-group-link :tag "Flymake" flymake)
+  :version "26.1")
+
+(defcustom python-flymake-command '("pyflakes")
+  "The external tool that will be used to perform the syntax check.
+This is a non empty list of strings, the checker tool possibly followed by
+required arguments: to use `flake8' you would set this to (\"flake8\" \"-\")."
+  :group 'python-flymake
+  :type '(repeat string))
+
+;; The default regexp accomodates for older pyflakes, which did not
+;; report the column number
+(defcustom python-flymake-command-output-regexp
+  "^\\(?:<stdin>\\):\\(?1:[0-9]+\\):\\(?:\\(?2:[0-9]+\\):\\)? \\(?3:.*\\)$"
+  "The regexp used to parse the output of the specified tool.
+It must contain two or three groups: group 1 is the line number, group 2 the
+optional column number and the third is the actual message."
+  :group 'python-flymake
+  :type 'regexp)
+
+(defcustom python-flymake-msg-alist
+  '(("\\(^redefinition\\|.*unused.*\\|used$\\)" . :warning))
+  "Alist used to associate messages to their types.
+Each element should be a cons-cell (REGEXP . TYPE), where TYPE must be
+one defined in the variable `flymake-diagnostic-types-alist'.
+For example, when using `flake8' a possible configuration could be:
+
+  ((\"\\(^redefinition\\|.*unused.*\\|used$\\)\" . :warning)
+   (\"^E999\" . :error)
+   (\"^[EW][0-9]+\" . :note))
+
+By default messages are considered errors."
+  :group 'python-flymake
+  :type `(alist :key-type (regexp)
+                :value-type (symbol)))
+
+(defvar-local python--flymake-proc nil)
+
+(defun python-flymake (report-fn &rest _args)
+  "Flymake backend for Python.
+This backend uses `python-flymake-command' (which see) to launch a process
+that is passed the current buffer's content via stdin.
+REPORT-FN is Flymake's callback function."
+  (unless (executable-find (car python-flymake-command))
+    (error "Cannot find a suitable checker"))
+
+  (unless (derived-mode-p 'python-mode)
+    (error "Can only work on `python-mode' buffers"))
+
+  (when (process-live-p python--flymake-proc)
+    (kill-process python--flymake-proc))
+
+  (let ((source (current-buffer)))
+    (save-restriction
+      (widen)
+      (setq python--flymake-proc
+            (make-process
+             :name "python-flymake"
+             :noquery t
+             :connection-type 'pipe
+             :buffer (generate-new-buffer " *python-flymake*")
+             :command python-flymake-command
+             :sentinel
+             (lambda (proc _event)
+               (when (eq 'exit (process-status proc))
+                 (unwind-protect
+                     (when (eq proc python--flymake-proc)
+                       (with-current-buffer (process-buffer proc)
+                         (goto-char (point-min))
+                         (cl-loop
+                          while (search-forward-regexp
+                                 python-flymake-command-output-regexp nil t)
+                          for msg = (match-string 3)
+                          for (beg . end) = (flymake-diag-region
+                                             source
+                                             (string-to-number (match-string 1))
+                                             (and (match-string 2)
+                                                  (string-to-number
+                                                   (match-string 2))))
+                          for type = (or (assoc-default msg
+                                                        python-flymake-msg-alist
+                                                        #'string-match)
+                                         :error)
+                          collect (flymake-make-diagnostic
+                                   source beg end type msg)
+                          into diags
+                          finally (funcall report-fn diags))))
+                   (kill-buffer (process-buffer proc)))))))
+      (process-send-region python--flymake-proc (point-min) (point-max))
+      (process-send-eof python--flymake-proc))))
+
+(defun python-flymake-activate ()
+  "Activate the Flymake syntax check on all python-mode buffers."
+  (add-hook 'flymake-diagnostic-functions #'python-flymake nil t))
+
+
 (defun python-electric-pair-string-delimiter ()
   (when (and electric-pair-mode
              (memq last-command-event '(?\" ?\'))
-- 
2.15.0.rc0