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 first bug is further instances of the bug in bug#63811 that made the
todo-mode buffer manually editable and hence susceptible to file format
corruption.  In that bug report I only looked at item editing, but now
I've reviewed all cases in todo-mode.el where buffer-read-only is set to
nil and found that a number of them could give rise to the same issue.
I have fixed these in the same way, by restricting the the scope of nil
buffer-read-only.

The second bug I encountered while testing one case of the
buffer-read-only bugs: currently, when moving a block of done items to
another category that does not already have done items, only the first
moved done item gets relocated to the target category's done section;
the remaining moved done items wrongly end up in the todo section of the
following category in the file, and since these items are tagged as
done, this breaks the format of non-done todo items.  The patch makes
sure the moved items are correctly relocated.

The third bug I discovered after reading the report of bug#54612, which
is about unintendend truncation of sexps resulting from the user
globally setting print-length or print-level to a sufficiently small
value.  The internal file format of todo-mode makes crucial use of
specially formatted sexps that are part of the file contents, and if
these get truncated, that can break the required format and cause errors
when using todo-mode commands.  This is prevented by binding
print-{length,level} to nil, as in the fix for bug#54612.

The fourth bug is a doc bug: the doc string of one todo-mode user option
refers to use of a todo-mode insertion command argument that, quite
embarrassingly, is a remnant of an earlier state of my revision of
todo-mode.el and was actually eliminated before the revision was merged
into the Emacs trunk ten years ago.  The patch replaces this obsolete
doc string with a description of the current behavior (which fortunately
is already correctly documented in the Todo mode info manual).

Since these four bugs are conceptually independent of each other, I
would like to install the fixes in separate commits; is that all right?


2023-06-26  Stephen Berman  <stephen.berman@gmx.net>

	Avoid making todo mode buffers manually editable

	* todo-mode.el (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.