bug#22663: python-mode: Fix electric indent bug after dedenting colon

[Joel Rosdahl <joel@rosdahl.net>]

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This fixes bug #22663 ("25.0.91; python.el electric-indent misbehaviour
with 'except:'"). Note that the bug is not restricted to "except:" but
affects all statements that are dedented by an electric colon.

For instance, entering a colon after "else" in

    if do:
        something()
        else
    outside

results in

    if do:
        something()
    else:
        outside

before the bug fix but

    if do:
        something()
    else:
    outside

after the bug fix.

-- Joel

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From 555fb47d0c3061346c2792e97206a0d64dd1e578 Mon Sep 17 00:00:00 2001
From: Joel Rosdahl <joel@rosdahl.net>
Date: Sun, 12 Feb 2017 16:10:47 +0100
Subject: [PATCH] python-mode: Fix electric indent bug after dedenting colon

This fixes bug #22663 ("25.0.91; python.el electric-indent misbehaviour
with 'except:'"). Note that the bug is not restricted to "except:" but
affects all statements that are dedented by an electric colon.

For instance, entering a colon after "else" in

    if do:
        something()
        else
    outside

results in

    if do:
        something()
    else:
        outside

before the bug fix but

    if do:
        something()
    else:
    outside

after the bug fix.
---
 lisp/progmodes/python.el            | 19 ++++++++++---------
 test/lisp/progmodes/python-tests.el |  3 +++
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 90b5e4e..467ac08 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -1286,16 +1286,17 @@ python-indent-post-self-insert-function
            (not (equal ?: (char-before (1- (point)))))
            (not (python-syntax-comment-or-string-p)))
       ;; Just re-indent dedenters
-      (let ((dedenter-pos (python-info-dedenter-statement-p))
-            (current-pos (point)))
+      (let ((dedenter-pos (python-info-dedenter-statement-p)))
         (when dedenter-pos
-          (save-excursion
-            (goto-char dedenter-pos)
-            (python-indent-line)
-            (unless (= (line-number-at-pos dedenter-pos)
-                       (line-number-at-pos current-pos))
-              ;; Reindent region if this is a multiline statement
-              (python-indent-region dedenter-pos current-pos)))))))))
+          (let ((start (copy-marker dedenter-pos))
+                (end (point-marker)))
+            (save-excursion
+              (goto-char start)
+              (python-indent-line)
+              (unless (= (line-number-at-pos start)
+                         (line-number-at-pos end))
+                ;; Reindent region if this is a multiline statement
+                (python-indent-region start end))))))))))
 
 \f
 ;;; Mark
diff --git a/test/lisp/progmodes/python-tests.el b/test/lisp/progmodes/python-tests.el
index 1e6b867..e911921 100644
--- a/test/lisp/progmodes/python-tests.el
+++ b/test/lisp/progmodes/python-tests.el
@@ -1130,10 +1130,13 @@ python-tests-visible-string
 if do:
     something()
     else
+outside
 "
    (python-tests-look-at "else")
    (goto-char (line-end-position))
    (python-tests-self-insert ":")
+   (should (= (current-indentation) 0))
+   (python-tests-look-at "outside")
    (should (= (current-indentation) 0))))
 
 (ert-deftest python-indent-electric-colon-3 ()
-- 
2.7.4