Re: cc-mode: Make all parameters introduced in Emacs 26 optional

[Matthew Carter <m@ahungry.com>]

Alan Mackenzie <acm@muc.de> writes:

> Hello, Jostein.
>
> On Mon, Jan 22, 2018 at 09:09:21 +0100, Jostein Kjønigsen wrote:
>> Hey everyone.
>
>> While cc-mode seems to be a foundation for lots of the major-modes
>> shipped with Emacs, it's also used by third-party packages.
>> For major-modes shipped with Emacs, changes to the core cc-mode
>> functions is not that big of a problem, since they can be changed in
>> tandem with the changes to cc-mode itself.
>
>> For third party modules (like csharp-mode, which I maintain), changes to
>> cc-mode core-functions are more problematic due to Emacs lacking
>> reliable introspection capabilities.
>
> There's a convention in CC Mode that functions, macros, and variables
> with a doc string are regarded as part of an "API" to derived modes, but
> objects with merely a "doc comment" are regarded as internal to CC Mode,
> and _much_ less secure against random changes.
>
>> As an example in the Emacs 26 branch c-font-lock-declarators is now
>> declared like this:
>> (defun c-font-lock-declarators (limit list types not-top &optional template-
>> class)  ...)
>> While in Emacs 25.3 and earlier it's declared like this:
>
>> (defun c-font-lock-declarators (limit list types)
>>   ...)
>
>> Basically the number of mandatory parameters has been bumped from 3 to
>> 4, with another optional parameter added.
>
> c-font-lock-declarators is one of these functions intended to be
> "internal".  If a derived mode like csharp-mode is using it directly,
> one of the following is true:
> (i) There's a need for functionality which is currently lacking in CC
> Mode.
> (ii) The maintainer of the derived mode is unaware of existing CC Mode
> functionality which would satisfy his need.
> (iii) ???
>
>> These kinds of changes makes it harder for third party modules to
>> maintain compatibility across Emacs-versions.
>
> Why is csharp-mode using c-font-lock-declarators at all?  Could it be
> you're wanting to do something which currently can't be done with the
> "API" functions/macros/variables?  If so, it might well be better to
> amend CC Mode to provide this functionality.
>
>> Wouldn't it be better to make *all *the new parameters optional and thus
>> maintain compatibility? Are there any good reasons not to do so?
>
> Well, to work properly, the caller of c-font-lock-declarators will need
> to determine the `not-top' argument rather than just relying on a
> randomish default.  The meaning of the function has changed.  `not-top'
> doesn't seem suitable for being &optional.
>
> Again, why is csharp-mode using this function?  Are there any other
> "internal" functions/macros/variables it is using?
>
>> --
>> Regards
>> Jostein Kjønigsen
>
>> jostein@kjonigsen.net 🍵 jostein@gmail.com
>> https://jostein.kjonigsen.net

Somewhat on this subject - recent versions of Emacs have seemed to have
changed single quotes with text between the quotes with a length greater
than 1 to use a warn font face on the quotes, instead of the font string
face (likely because in C the single quote denotes a char, but in many
of the derived modes that cc-mode mentions in it's own comment set
(php-mode, dart-mode etc.), a single quoted string and double quoted
string are used interchangeably).

Does cc-mode have a setting to correct this and restore the old behavior?

-- 
Matthew Carter (m@ahungry.com)
http://ahungry.com