bug#6459: 24.0.50; completions-format should not have a `nil' choice

[Lennart Borgman <lennart.borgman@gmail.com>]

On Sat, Jun 19, 2010 at 4:37 PM, Juri Linkov <juri@jurta.org> wrote:
>> (defcustom completions-format nil
>>   "Define the appearance and sorting of completions.
>> If the value is `vertical', display completions sorted vertically
>> in columns in the *Completions* buffer.
>> If the value is `horizontal' or nil, display completions sorted
>> horizontally in alphabetical order, rather than down the screen."
>>   :type '(choice (const nil) (const horizontal) (const vertical))
>>   :group 'minibuffer
>>   :version "23.2")
>>
>> There is no reason for the `nil' choice.  Please remove it and make the
>> default value `horizontal'.  Occam's razor (KISS) and clarity for users
>> argue for this.
>
> We could remove nil from the docstring and from :type, and change
> the default value to `horizontal', but I'd still treat nil as
> `horizontal' internally for compatibility.


Since this is a new defcustom woulddn't it be better to not let nil be
a valid value? That may catch some problems and the backward
compatibilities are not likely to be big.