bug#40421: 26.2; (And 27.0.90) Inconsistent fontifying in c-mode

[Rolf Ade]

Hello Alan,

Alan Mackenzie <acm@muc.de> writes:
> In article <mailman.96.1585962545.2644.bug-gnu-emacs@gnu.org> you wrote:
>
>> Recipt:
>
>> emacs -Q
>
>> Insert:
>
>> /* 11 */
>> EXTERN int              XML_GetCurrentByteCount(XML_Parser parser);
>> /* 12 */
>> EXTERN enum XML_Status  XML_SetBase(XML_Parser parser, const XML_Char *base);
>> /* 13 */
>> EXTERN const XML_Char *  XML_GetBase(XML_Parser parser);
>> /* 14 */
>> EXTERN int              XML_GetSpecifiedAttributeCount(XML_Parser parser);
>> /* 15 */
>
>> and M-x c-mode. The font-look seems randomly. Some EXTERN colered, some
>> not, some function names black, some blue.
>
> Yes.  The problem here is that these declarations aren't syntactically
> correct C.  To C Mode, "EXTERN" just looks like an ordinary identifier,
> not a macro which (presumably) expands to "extern".

To that, or, depending on the build evironment, to something similar,
yes.

I can understand, that c-mode doesn't get this right. But part of the
point was the apparent randomly switching of the fontification. Getting
the colors wrong is one thing (but c-mode don't even got it wrong, for
the first handful of function prototypes), but getting it wrong
inconstently irritates particularly.

But, yes ...

> I would recommend you to use CC Mode's "noise macro" facility here.
> (See the CC Mode manual.)  With this, you would tell CC Mode that
> "EXTERN" just "expands to nothing", and thus won't interfere with the
> syntactic analysis.  One way to do this is to set c-noise-macro-names in
> a hook function, probably c-mode-common-hook.  Another way (if you don't
> have many source files) would be to set that variable in a file local
> variables section (see the Emacs manual) - for example, put the
> following at the end of your C file:
>
>     /* Local Variables: */
>     /* c-noise-macro-names: ("EXTERN") */
>     /* END: */
>
> .  Then restart C Mode with M-x c-mode.  The fontification should now
> look OK.

... that works well, thanks.

Sorry for the noise.

>> The whole (small) file is here
>> http://tdom.org/index.html/raw/generic/tdomDecls.h?name=cccb9227. With
>> this syntactically correct file (at least gcc and clang consume it
>> without complain) there is similiar font-lock flicker around the lines
>> commented with 12, 13, 14.
>
> Thanks for taking the trouble to reduce the problem to a minimal test
> case.  That's appreciated.
>
>> I report this (and see it) on my working-place emacs-26.2 but have
>> verified, that a freshly build emacs-27.0.90 shows the same behaviour.