bug#27158: 25.2; Eliminating old usage of completing-read from built-in files

[Dmitry Gutov]

On 5/31/17 8:52 AM, Drew Adams wrote:

> Would you make a default arg be mandatory instead of optional?
> Is that it?  If not, what default default would you propose?

It's not necessary.

> What should be returned if no explicit default is provided and
> the user hits RET with no input?

Prohibit them from finishing completion, except through entering a valid 
value, or pressing C-g.

> IN any case, nothing stops someone from defining their own
> `my-completing-read', which does not have this feature, er,
> quirk.  I don't see the problem.

That doesn't help if we want to augment completing-read-function and all 
packages using it.