Re: generic color support for `texinfo.tex`

[Jean Abou Samra]

Le 24/11/2021 à 21:50, Gavin Smith a écrit :
> On Wed, Nov 24, 2021 at 3:17 PM Werner LEMBERG <wl@gnu.org> wrote:
> > For the LilyPond documentation we are going to use `pygments` to do
> > automatic colour highlighting of LilyPond snippets.  We also want to
> > support this feature in the PDF manuals.  To do so I ask you to apply
> > something like the following patch to make `@setcolor` work in
> > `@example` environments, too.
> I'm not sure why it's needed; could you send an example of the kind of
> input you are trying to make work?
>
> I am guessing that it is @setcolor with an argument inside of @example, like
>
> @example
> test
> @setcolor{0.7 0.7 0.2}brown
> @end example
>
> This doesn't work, as you found out. To work around this, you can
> define a macro:
>
> @tex
> \global\def\colorBrown{0.7 0.7 0.2}
> @end tex
>
> @example
> test
> @setcolor{@colorBrown}brown
> @end example
>
> This works because the catcode of the space is "fixed" at the time of
> the macro definition.
>
> (Obviously this should be conditional on TeX and probably PDF output
> in your document, using @iftex and so on.)
>
> Catcodes are a confusing part of texinfo.tex and I'd rather not have
> to do anything to make them more complicated. I'm not convinced that
> your change would always work; for example, if the @setcolor command
> is nested inside the argument to another command, then it's possible
> that spaces inside its argument have their catcodes fixed at the time
> of that argument being read, depending on how the other command was
> defined.
>
> Do you think that the workaround I suggested would be good enough for
> your purposes?


There's a bit more work involved in our highly complex
build system to output an includable file comprising
these color definitions. I can probably get it to work
though.

The one case where it would become somewhat more
inconvenient is if someone (I'm not focusing on it
right now) tries to upstream the small Texinfo
Pygments formatter that we're using. The Formatter
API has a get_style_defs() method of Formatter object,
which is supposed to output the style definitions
required once to define highlighting colors. In HTML,
this is a CSS stylesheet; in LaTeX, it defines commands
for styling each token type. This API is accessible
through a switch of the command-line interface. It
would be a bit tricky to define what it returns for
Texinfo since there would be one CSS stylesheet and one
bit of content in Texinfo syntax for TeX. However,
it can probably be dealt with by slightly hijacking
the string parameter of get_style_defs(), which
is supposed to define a kind of prefix (inserted
as a level of specificity before class names in
CSS and taken as a command prefix in LaTeX) to
support things like "css" or
"css;css_prefix='.highlight-class'".



> > It would be nice to have `@setcolor` as an 'official' command that
> > also works with other output formats (for info, this would probably be
> > a no-op), but we can live without that since we let `pygments`
> > directly manipulate the HTML output.
> Good to hear that you are managing to do syntax highlighting in HTML.


Pygments does all the work for us. It's a nifty
library.

Best regards,
Jean