mdBook/examples/de-emphasize.rs

//! An example preprocessor for removing all forms of emphasis from a markdown
//! book.
use mdbook::book::{Book, BookItem, Chapter};
use mdbook::errors::{Error, Result};
use mdbook::preprocess::{Preprocessor, PreprocessorContext};
use pulldown_cmark::{Event, Parser, Tag};
use pulldown_cmark_to_cmark::fmt::cmark;

const NAME: &str = "md-links-to-html-links";

fn main() {
    panic!("This example is intended to be part of a library");
}

#[allow(dead_code)]
struct Deemphasize;

impl Preprocessor for Deemphasize {
    fn name(&self) -> &str {
        NAME
    }

    fn run(&self, _ctx: &PreprocessorContext, mut book: Book) -> Result<Book> {
        eprintln!("Running '{}' preprocessor", self.name());
        let mut num_removed_items = 0;

        process(&mut book.sections, &mut num_removed_items)?;

        eprintln!(
            "{}: removed {} events from markdown stream.",
            self.name(),
            num_removed_items
        );

        Ok(book)
    }
}

fn process<'a, I>(items: I, num_removed_items: &mut usize) -> Result<()>
where
    I: IntoIterator<Item = &'a mut BookItem> + 'a,
{
    for item in items {
        if let BookItem::Chapter(ref mut chapter) = *item {
            eprintln!("{}: processing chapter '{}'", NAME, chapter.name);

            let md = remove_emphasis(num_removed_items, chapter)?;
            chapter.content = md;
        }
    }

    Ok(())
}

fn remove_emphasis(num_removed_items: &mut usize, chapter: &mut Chapter) -> Result<String> {
    let mut buf = String::with_capacity(chapter.content.len());

    let events = Parser::new(&chapter.content).filter(|e| {
        let should_keep = match *e {
            Event::Start(Tag::Emphasis)
            | Event::Start(Tag::Strong)
            | Event::End(Tag::Emphasis)
            | Event::End(Tag::Strong) => false,
            _ => true,
        };
        if !should_keep {
            *num_removed_items += 1;
        }
        should_keep
    });

    cmark(events, &mut buf, None)
        .map(|_| buf)
        .map_err(|err| Error::from(format!("Markdown serialization failed: {}", err)))
}