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Re: Error in C++ mode with Emacs 27.0.90


From: Dmitry Gutov
Subject: Re: Error in C++ mode with Emacs 27.0.90
Date: Mon, 30 Mar 2020 01:32:48 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 29.03.2020 14:50, Alan Mackenzie wrote:

It seems unlikely that we can get a nested list (in imenu--index-alist)
with only one element.  I have tried creating a C++ buffer with 25
functions in it.  This gives a simple list of 25 elements.  With 26
functions, I get a nested alist with two elements.

What's the worst that can happen in this case? We get a nested submenu with just one element?

However, in an emacs-lisp-mode buffer, we get things like "Variables"
and "*Rescan*", but I've not yet succeeded in causing a nested list with
just one element.  I'm not convinced enough that it couldn't happen,
though.

The latter part of the function looks like this (before my patch):

         (let* ((menu (imenu--split-menu index-alist
                                         (buffer-name)))
                (menu1 (imenu--create-keymap (car menu)
========>                                   (cdr (if (< 1 (length (cdr menu)))
                                                      menu
                                                    (car (cdr menu))))
                                             'imenu--menubar-select)))
           (setcdr imenu--menubar-keymap (cdr menu1)))))))

That `if' form has been there since imenu-update-menubar was first
written by Karl Heuer in 1997 (commit 0a8e8bc63e3).  Presumably, it
really was needed back then.

If you're implying we can get rid of the check and always return (cdr menu), I say let's try.

In any case, imenu--create-keymap is also called from imenu--mouse-menu,
which probably needs the same kind of fix.

Possibly.  I've not managed to create the same error in
imenu--mouse-menu,

  (setq imenu-use-popup-menu t)

followed by

  M-x imenu

did that for me in the example buffer.

but perhaps it could do with the same correction,
just in case.  What do you think?

Yup.

Incidentally, that patch from last night was a bit untidy.  I think it
needs cleaning up a bit.

So how about this one? In my very brief testing, it seems to work, both in the example buffer, and for imenu indices in several bigger files:

diff --git a/lisp/imenu.el b/lisp/imenu.el
index fb8b3de662..809ddd7ed1 100644
--- a/lisp/imenu.el
+++ b/lisp/imenu.el
@@ -814,9 +814,7 @@ imenu--mouse-menu
   (setq index-alist (imenu--split-submenus index-alist))
   (let* ((menu (imenu--split-menu index-alist (or title (buffer-name))))
         (map (imenu--create-keymap (car menu)
-                                   (cdr (if (< 1 (length (cdr menu)))
-                                            menu
-                                          (car (cdr menu)))))))
+                                   (cdr menu))))
     (popup-menu map event)))

 (defun imenu-choose-buffer-index (&optional prompt alist)
@@ -912,9 +910,7 @@ imenu-update-menubar
        (let* ((menu (imenu--split-menu index-alist
                                         (buffer-name)))
                (menu1 (imenu--create-keymap (car menu)
-                                           (cdr (if (< 1 (length (cdr menu)))
-                                                    menu
-                                                  (car (cdr menu))))
+                                           (cdr menu)
                                            'imenu--menubar-select)))
          (setcdr imenu--menubar-keymap (cdr menu1)))))))




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