Add additional-hljs-packages option

[Evian-Zhang]

As a syntax highlighting tool, highlight.js supports 3rd party languages (see instructions here) since they don't currently merge new grammars into core. This can be done by placing additional JavaScript files alongside hightlight.js's js file, and then call the syntax highlighting functions provided by hljs, such as hightlightBlock used in our book.js.

However, this can't be done currently in mdbook, since the additional-js field is designed for js files called after the main book.js, while placing the highlight.js 3rd packages there leads to highlightBlock called before those packages loaded. On the other hand, moving js files specified in additional-js field above the book.js may lead to unexpected behaviors, since it is supposed to be executed after the book.js is executed.

So adding another field, additional-hljs-packages, could solve this problem, which will place those js files between the highlight.js's js file and book.js.

[KFearsoff]

Thanks for your contribution!

Your use case is definitely valid, but I feel like the approach is maybe a little too heavy-handed this time. It is not documented as well as it probably should be, but you can actually just edit the HTML template that the pages get rendered on!

First, you would init mdbook with --init flag, and then you would edit index.hbs - index.hbs is basically an HTML file with very little bits of Handlebars templating. So you would be able to just add all of the necessary JS script includes directly to your HTML!

@rustbot label +C-question +S-waiting-on-author

[Evian-Zhang]

Oh yes, I forgot this way. Thank you!