1 files changed, 145 insertions, 6 deletions

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 895117b9ee3..d4226e5ce7b 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -2113,20 +2113,25 @@ remote host, the returned value is intended for
 (defun python-shell-calculate-exec-path ()
   "Calculate `exec-path'.
 Prepends `python-shell-exec-path' and adds the binary directory
-for virtualenv if `python-shell-virtualenv-root' is set.  If
-`default-directory' points to a remote host, the returned value
-appends `python-shell-remote-exec-path' instead of `exec-path'."
+for virtualenv if `python-shell-virtualenv-root' is set - this
+will use the python interpreter from inside the virtualenv when
+starting the shell.  If `default-directory' points to a remote host,
+the returned value appends `python-shell-remote-exec-path' instead
+of `exec-path'."
   (let ((new-path (copy-sequence
                    (if (file-remote-p default-directory)
                        python-shell-remote-exec-path
-                     exec-path))))
+                     exec-path)))
+
+        ;; Windows and POSIX systems use different venv directory structures
+        (virtualenv-bin-dir (if (eq system-type 'windows-nt) "Scripts" "bin")))
     (python-shell--add-to-path-with-priority
      new-path python-shell-exec-path)
     (if (not python-shell-virtualenv-root)
         new-path
       (python-shell--add-to-path-with-priority
        new-path
-       (list (expand-file-name "bin" python-shell-virtualenv-root)))
+       (list (expand-file-name virtualenv-bin-dir python-shell-virtualenv-root)))
       new-path)))
 
 (defun python-shell-tramp-refresh-remote-path (vec paths)
@@ -5142,6 +5147,138 @@ returned as is."
   (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.  Once launched it will receive the Python source to be
+checked as its standard input.
+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, and at the same time it's compatible with
+;; flake8 output, although it may be redefined to explicitly match the
+;; TYPE
+(defcustom python-flymake-command-output-pattern
+  (list
+   "^\\(?:<?stdin>?\\):\\(?1:[0-9]+\\):\\(?:\\(?2:[0-9]+\\):\\)? \\(?3:.*\\)$"
+   1 2 nil 3)
+  "Specify how to parse the output of `python-flymake-command'.
+The value has the form (REGEXP LINE COLUMN TYPE MESSAGE): if
+REGEXP matches, the LINE'th subexpression gives the line number,
+the COLUMN'th subexpression gives the column number on that line,
+the TYPE'th subexpression gives the type of the message and the
+MESSAGE'th gives the message text itself.
+
+If COLUMN or TYPE are nil or that index didn't match, that
+information is not present on the matched line and a default will
+be used."
+  :group 'python-flymake
+  :type '(list regexp
+               (integer :tag "Line's index")
+               (choice
+                (const :tag "No column" nil)
+                (integer :tag "Column's index"))
+               (choice
+                (const :tag "No type" nil)
+                (integer :tag "Type's index"))
+               (integer :tag "Message's index")))
+
+(defcustom python-flymake-msg-alist
+  '(("\\(^redefinition\\|.*unused.*\\|used$\\)" . :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-parse-output (source proc report-fn)
+  "Collect diagnostics parsing checker tool's output line by line."
+  (let ((rx (nth 0 python-flymake-command-output-pattern))
+        (lineidx (nth 1 python-flymake-command-output-pattern))
+        (colidx (nth 2 python-flymake-command-output-pattern))
+        (typeidx (nth 3 python-flymake-command-output-pattern))
+        (msgidx (nth 4 python-flymake-command-output-pattern)))
+    (with-current-buffer (process-buffer proc)
+      (goto-char (point-min))
+      (cl-loop
+       while (search-forward-regexp rx nil t)
+       for msg = (match-string msgidx)
+       for (beg . end) = (flymake-diag-region
+                          source
+                          (string-to-number
+                           (match-string lineidx))
+                          (and colidx
+                               (match-string colidx)
+                               (string-to-number
+                                (match-string colidx))))
+       for type = (or (and typeidx
+                           (match-string typeidx)
+                           (assoc-default
+                            (match-string typeidx)
+                            python-flymake-msg-alist
+                            #'string-match))
+                      (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)))))
+
+(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"))
+
+  (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 (with-current-buffer source
+                             (eq proc python--flymake-proc))
+                       (python--flymake-parse-output source proc report-fn))
+                   (kill-buffer (process-buffer proc)))))))
+      (process-send-region python--flymake-proc (point-min) (point-max))
+      (process-send-eof python--flymake-proc))))
+
+
 (defun python-electric-pair-string-delimiter ()
   (when (and electric-pair-mode
              (memq last-command-event '(?\" ?\'))
@@ -5255,7 +5392,9 @@ returned as is."
   (make-local-variable 'python-shell-internal-buffer)
 
   (when python-indent-guess-indent-offset
-    (python-indent-guess-indent-offset)))
+    (python-indent-guess-indent-offset))
+
+  (add-hook 'flymake-diagnostic-functions #'python-flymake nil t))
 
 
 (provide 'python)