Fix invalid search bound error in python-shell-completion-at-point

* lisp/progmodes/python.el (python-shell-completion-at-point): Add
check if point is before line-start.
* test/lisp/progmodes/python-tests.el (python-shell-completion-shell-buffer-1)
(python-shell-completion-shell-buffer-native-1): New tests
(bug#58548).

1 files changed, 12 insertions, 9 deletions

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 50f1e6752e4..11195894234 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -4080,15 +4080,18 @@ using that one instead of current buffer's process."
                  (buffer-substring-no-properties line-start (point)))
             (buffer-substring-no-properties line-start (point))))
          (start
-          (save-excursion
-            (if (not (re-search-backward
-                      (python-rx
-                       (or whitespace open-paren close-paren string-delimiter simple-operator))
-                      line-start
-                      t 1))
-                line-start
-              (forward-char (length (match-string-no-properties 0)))
-              (point))))
+          (if (< (point) line-start)
+              (point)
+            (save-excursion
+              (if (not (re-search-backward
+                        (python-rx
+                         (or whitespace open-paren close-paren
+                             string-delimiter simple-operator))
+                        line-start
+                        t 1))
+                  line-start
+                (forward-char (length (match-string-no-properties 0)))
+                (point)))))
          (end (point))
          (prompt-boundaries
           (with-current-buffer (process-buffer process)