[Emacs-diffs] emacs-25 3ef4ee8: Avoid infloop in python

[Daniel Colascione]

branch: emacs-25
commit 3ef4ee84fa3f658c2df802569dc89023d98e9947
Author: Daniel Colascione <address@hidden>
Commit: Daniel Colascione <address@hidden>

    Avoid infloop in python
    
    Fix bug#24905
    
    * lisp/progmodes/python.el (python-info-docstring-p): Improve
    infloop avoidance: replace (bobp) with generic test for
    forward progress.
    * test/lisp/progmodes/python-tests.el (python-bob-infloop-avoid): Add
    test for bug#24905
---
 lisp/progmodes/python.el       |   11 +++++++++--
 test/automated/python-tests.el |    7 +++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 9091289..d0d4a7f 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -4865,12 +4865,19 @@ point's current `syntax-ppss'."
              ;; Allow up to two consecutive docstrings only.
              (>=
               2
-              (progn
+              (let (last-backward-sexp-point)
                 (while (save-excursion
                          (python-nav-backward-sexp)
                          (setq backward-sexp-point (point))
                          (and (= indentation (current-indentation))
-                              (not (bobp)) ; Prevent infloop.
+                              ;; Make sure we're always moving point.
+                              ;; If we get stuck in the same position
+                              ;; on consecutive loop iterations,
+                              ;; bail out.
+                              (prog1 (not (eql last-backward-sexp-point
+                                               backward-sexp-point))
+                                (setq last-backward-sexp-point
+                                      backward-sexp-point))
                               (looking-at-p
                                (concat "[uU]?[rR]?"
                                        (python-rx string-delimiter)))))
diff --git a/test/automated/python-tests.el b/test/automated/python-tests.el
index 54ed922..f6564dd 100644
--- a/test/automated/python-tests.el
+++ b/test/automated/python-tests.el
@@ -2452,6 +2452,13 @@ if x:
                 (line-beginning-position) (line-end-position))
                "abcdef")))))
 
+(ert-deftest python-bob-infloop-avoid ()
+  "Test that strings at BOB don't confuse syntax analysis.  Bug#24905"
+  (python-tests-with-temp-buffer
+      " \"\n"
+    (goto-char (point-min))
+    (font-lock-fontify-buffer)))
+
 
 ;;; Shell integration