bug#19112: 25.0.50; todo-mode: error on empty, file-less buffers

[Stephen Berman <stephen.berman@gmx.net>]

On Wed, 19 Nov 2014 22:44:22 +0100 Simen Heggestøyl <simenheg@gmail.com> wrote:

> Todo mode crashes when activated in an empty, file-less buffer.
>
> Reproduced by the following recipe from Emacs -Q:
> 1. Switch to a new buffer, so that it's empty, and not connected to
> a file.
> 2. Run `M-x todo-mode'.
>
> This should produce the following error message:
>
> todo-mode: Wrong type argument: arrayp, nil
>
> In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.4)
> of 2014-11-19 on x240
> Repository revision: f5d77aafa9d59c4afb13d744e67a0e4daf3be31a
> Windowing system distributor `The X.Org Foundation', version 11.0.11601901
> System Description: Debian GNU/Linux testing (jessie)

Thanks for the report.  Before I try to fix this, I'd like to know why
you carried out the above recipe: did you just happen to discover that
Emacs has this package and wonder what it is and so just decided to
invoke todo-mode in an empty buffer and see what happens?  The reason
I'm asking is that `M-x todo-mode' is not one of the documented entry
points, and in normal operation of Todo mode it should never be
necessary to call todo-mode.  Moreover, most of Todo mode is not
designed to work with non-file buffers; there are exceptions, but they
are (intended to be) available only after you've added at least one todo
file, by typing `M-x todo-show', as documented (both in the Commentary
of the source code and in the Todo Mode Info manual).  So knowing why
you typed `M-x todo-mode' on an empty buffer will help me to decide how
to avoid the error.  Thanks.

Steve Berman