bug#58883:

Alan Mackenzie <[email protected]> writes:

> Hello, Po.
>
> On Tue, Nov 08, 2022 at 20:29:30 +0800, Po Lu wrote:
>> Alan Mackenzie <[email protected]> writes:
>
>> > I'm gradually fixing it.
>
>> Thanks.  I hope Emacs 29 will not be released without the fix.
>
>> > The mechanism is that when C Mode sees what it takes to be a type, from
>> > the context, c-forward-type returns the symbol 'maybe.
>
>> > Later on in the processing, the analysis of the C code "confirms" that
>> > this 'maybe actually is a type, and it gets promoted to 'found, and
>> > entered into the c-found-types list.  At the same time, other occurrences
>> > of the type throughout the buffer are fontified as types.
>
>> > This mechanism is not foolproof, and goes wrong when a statement is
>> > partially typed.  Rather than correcting the mistakenly fontified
>> > "types", which would be more difficult, I'm concentrating on not
>> > promoting a 'maybe type to a 'found type too enthusiasically.
>
>> Right, but there are some things that simply cannot work with that
>> approach.  Imagine the following code being typed by the user:
>
>> foo (ptr)
>>      struct foobar *ptr;
>> {
>>   register struct frobar *ptr_fast;
>
>>   ptr_fast = ptr;
>
>> only for him to realize that "oops, struct frobar is not a type!" and
>> correct it to:
>
>>   register struct foobar *ptr_fast;
>
>> by which time it is too late, and "struct frobar" is now in
>> c-found-types, with all the ensuing consequences.
>
> I don't think this happens for struct/union/enum/class/... tags anymore.
> But I think it still does for other types of types.  Mostly having a
> mis-typed identifier in c-found-types shouldn't annoy too much, unless
> it's some other sort of identifier in the code.

So if the typo turns from:

  register struct frobar *...

to

  register frobar *...

there will be a problem?  That's not very reassuring.

> There were loud complaints around 18 months ago about CC Mode's
> fontification being "random", together with pressure to fix it.  The
> thread on emacs-devel was started by Daniel Colascione on 2021-06-03 with
> subject line "cc-mode fontification feels random".  The current
> compromise arose out of that thread.

I suggest turning the compromise off by default.  People who care about
``random'' fontification can then turn it on, or use the new tree-sitter
modes if they can.

Misfontificiation is a much more serious problem than fontification
being ommitted for unconventional-looking types!

> As I say, I think CC Mode has pretty much reached the end of the road as
> far as indentation and (particularly) fontification go.  Any fix of one
> particular problem leads to other problems springing up.  I think we must
> look forward to the upcoming tree-sitter new modes.  I will be trying to
> break these with CC Mode's test suite and 20 years' worth of bug reports
> with unusual cases in them.  ;-)

Tree-sitter has many problems.  For one, it does not intend to support
C89 or (more importantly for me) pre-standard C.

Thanks.