bug#54296: Add buffer-matching functionality

[Dmitry Gutov]

On 13.06.2022 15:13, Eli Zaretskii wrote:
> My "still don't think I understand" comment was about the need to
> support major-mode when apparently the_only_  user of that is
> fundamental-mode, where we cannot use derived-mode instead.

There are two uses of it inside project-kill-buffer-conditions.

One is

  (major-mode . fundamental-mode)

, and another is

  (and (derived-mode . special-mode)
         (not (major-mode . help-mode)))

I suppose in the latter it doesn't really matter whether the check uses 
'derived-mode-p', but the current way is more conservative.

Also see the turn-on-font-lock-if-desired example from the other email.

> If indeed
> fundamental-mode is the only case where major-mode is useful, I asked
> why not use a predicate that tests explicitly for that case.

If a predicate is a lambda, then it's not as readable.

> And if I understand your reasoning above, then doesn't
>
>    (eq major-mode 'fundamental-mode)
>
> provide an easy default that can be read at a glance?

Are you proposing adding a "keyword" 'eq' which would have a variable 
name as its first arg and the value as its second arg?

That would work (aside from the backward compatibility concerns). It 
might look confusing to a Lisp programmer, resembling "regular" code too 
much, creating false expectations.