bug#64298: 29.0.92; Fixes for several todo-mode bugs

[Stephen Berman]

On Mon, 26 Jun 2023 14:48:43 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Date: Mon, 26 Jun 2023 11:39:35 +0200
>>
>> This report describes and provides patches for four different bugs in
>> todo-mode.el.  Three of the bugs can result in todo-mode file format
>> corruption, and the fourth is a documentation bug, so I think the fixes
>> should all be installed in the release branch, and I'm asking for
>> permission to do that.  As with my previous todo-mode bugfix, which also
>> went into the release branch (bug#63811), the patches touch only
>> todo-mode.el and with them all todo-mode unit tests pass.
>
> The 3rd and the 4th patches are okay for the release branch.  The
> first one looks OK, but how sure you are that you have identified all
> the places which need buffer-read-only bound to nil?  Did you exercise
> all the possible code paths in the places affected by this change?

I tested each todo-mode command in which buffer-read-only is bound to
nil, and the ones listed in the ChangeLog entry are the problematic
cases I found, where the buffer became writeable on entering the
minibuffer.  I thought that was sufficient, but thanks for making me
take another, and closer, look, because I had indeed overlooked two
cases where prompting for user input made the buffer writeable under
specific conditions that I had neglected to test.  I've now fixed these
cases with the revised first patch appended below (the first three hunks
are new, the rest the same as the first patch in my OP).

I cannot guarantee that all possibilities are now accounted for, but
systematically going through all combinations of commands and the
conditions under which they are executed would be very tedious and
time-consuming, and I think it's better to include fixes for the known
problems in emacs-29 rather than waiting for a possibly more
comprehensive fix.

One of the two cases, that of moving a todo-mode category from one todo
file to another, also revealed a bad UX effect.  Moving the category
requires applying `widen' (since todo-mode uses narrowing to show only
the current category's items), but in the current code the user is
prompted for the target file after widening, which makes the file's
internal structure visible, which is ugly and unnecessarily confusing.
I fixed this with the second attached patch (applied after the first
one) by narrowing again before the prompt and later widening again to
delete the content of the moved category.  This is a straightforward and
no-risk fix, so I hope it's also acceptable for emacs-29.

> The 2nd patch is the scariest.  How grave is it, and if it's grave,
> how come it was not reported until now?  In general, I'd prefer to
> have the 2nd patch on master, not on the release branch, at least for
> now.  (We could consider backporting it after Emacs 29.1 is released.)

I'm surprised you find this patch scary; what specifically do you think
is dangerous about it?  AFAICS it's a fairly straightforward fix that
accounts for a case I had failed to test: moving two or more done items
to a non-final category that doesn't yet have any done items.  Without
the fix, after inserting the first moved done item, the current code
using todo-forward-item moves point too far, into the todo section of
the next category and the remaining moved done items are inserted there,
with the result that many todo-mode commands will not apply to them
correctly, and executing such commands can mess up the category's counts
of todo and done items, leading at least to confusion.

AFAICT such problems don't lead to data loss and with some effort can be
repaired, but they shouldn't happen in the first place, and with the
fix, they don't.  And I don't think the fix can cause any other
problems, at least I haven't seen any in testing it.

As for why there has been no previous report of this bug, I guess it's
due to a combination of involving a relatively seldom needed command,
having triggering conditions that probably also don't occur very often,
and above all, there being presumably very few regular users of
todo-mode.  Admittedly, that combination speaks against the urgency of
committing the fix to emacs-29, but again, the problem is, if not grave,
at least very confusing, and AFAICT the fix works and is low-risk.

Finally, after I posted the bug report, I received private email from
someone requesting a further doc fix: the reference in the Commentary
section of todo-mode.el to "the Todo mode user manual, which is included
in the Info documentation" led this person to a futile search for
information about Todo mode in the Emacs Info manual.  So I would also
like to install the third attached patch to clarify that it's a separate
Info manual.

Steve Berman


2023-06-27  Stephen Berman  <stephen.berman@gmx.net>

        Avoid making todo mode buffers manually editable

        * lisp/calendar/todo-mode.el (todo-add-category)
        (todo-move-category, todo-edit-item--header)
        (todo-set-item-priority, todo-move-item, todo-item-undone)
        (todo-archive-done-item, todo-set-category-number): Restrict the
        scope of nil buffer-read-only to the function calls that change
        buffer text, thereby preventing todo mode buffers from becoming
        manually editable and hence possibly corrupted when the minibuffer
        is in use.

txtW9l17zU1zm.txt
Description: Avoid making todo mode buffers manually editable

2023-06-27  Stephen Berman  <stephen.berman@gmx.net>

        Avoid exposing todo file internal structure

        * todo-mode.el (todo-move-category): Restore display of selected
        category in source file, so internal file structure is not visible
        if user is prompted to choose a new category name in target file,
        and widen again to delete moved category from source file.

txtXcShIXuNDU.txt
Description: Avoid exposing todo file internal structure

2023-06-27  Stephen Berman  <stephen.berman@gmx.net>

        Clarify phrasing in the todo-mode.el Commentary

        * todo-mode.el: Explicitly note that the Todo mode user manual is
        a separate Info manual in the Emacs installation.

txtKf1gbfhvPB.txt
Description: Clarify phrasing in the todo-mode.el Commentary