Re: Template types not correctly highlighted in C++

[Alan M. <ac...@mu...>]

Hello, Ludwig.

Thanks for the bug report, and thanks even more for cutting it down to a
nice, small, easy to work with snippet.

On Mon, Feb 20, 2017 at 16:22:41 +0000, lu...@lu... wrote:
> Hello Alan,

> if you consider the below C++ code:

> // NotHighlighted is defined in another file.
> template<typename Baz>
> class Foo : public Bar<Baz> {
>    std::vector<NotHighlighted> foo;
> }

> With `emacs -Q` I get the display as shown in the attached file 
> template0.png. Note, the symbol "NotHighlighted" is not highlighted like 
> the symbol "Baz".

This is actually correct.  CC Mode doesn't know whether or not
"NotHighlighted" is a type or not; it could easily be a constant
integer.  (Yes, I know that std::vector always takes a type, but this
goes into semantics more than CC Mode wants to).

> If I erase '>' and put it back (just after "NotHighlighted"), the font 
> lock seems to be refreshed and this time the symbol "NotHighlighted" is 
> highlighted (see template1.png).

Yes, this seems to be a bug.  ;-)  That sequence of operations shouldn't
cause the fontification of "NotHighlighted".  I'm trying to track this
down at the moment.

CC Mode maintains a collection of "known types" for each buffer -
identifiers which are known from their contexts to be types.  Somehow,
"NotHighlighted" has got into this collection.  I will figure out soon
how and why.

> Note, if I add the following C++ line "class NotHighlighted;", it is 
> correct (cf. template2.png).

When you do this, "NotHighlighted" becomes a "known type" and the
fontification is then correct.

> Can you tell me if is an expected behavior? I would expected the 
> template argument to be colored in an homogeneous way across the code. 
> template[12].png seem correct.

See above.

The more fundamental question is whether an ambiguous template argument
should be fontified as a type or not.  Doing so will inevitably lead to
errors in places where the identifier actually isn't a type.

> Thanks for your time

Thank you again for the report!  I'll be back in touch again when I've
made more progress.

> Ludwig

> version: GNU Emacs 26.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 
> 2.24.28) of 2017-02-13

-- 
Alan Mackenzie (Nuremberg, Germany).