mdbook/src/cmd/watch.rs

use super::command_prelude::*;
use crate::{get_book_dir, open};
use ignore::gitignore::Gitignore;
use mdbook::errors::Result;
use mdbook::utils;
use mdbook::MDBook;
use pathdiff::diff_paths;
use std::path::{Path, PathBuf};
use std::sync::mpsc::channel;
use std::thread::sleep;
use std::time::Duration;

// Create clap subcommand arguments
pub fn make_subcommand() -> Command {
    Command::new("watch")
        .about("Watches a book's files and rebuilds it on changes")
        .arg_dest_dir()
        .arg_root_dir()
        .arg_open()
}

// Watch command implementation
pub fn execute(args: &ArgMatches) -> Result<()> {
    let book_dir = get_book_dir(args);
    let mut book = MDBook::load(book_dir)?;

    let update_config = |book: &mut MDBook| {
        if let Some(dest_dir) = args.get_one::<PathBuf>("dest-dir") {
            book.config.build.build_dir = dest_dir.into();
        }
    };
    update_config(&mut book);

    if args.get_flag("open") {
        book.build()?;
        let path = book.build_dir_for("html").join("index.html");
        if !path.exists() {
            error!("No chapter available to open");
            std::process::exit(1)
        }
        open(path);
    }

    trigger_on_change(&book, |paths, book_dir| {
        info!("Files changed: {:?}\nBuilding book...\n", paths);
        let result = MDBook::load(book_dir).and_then(|mut b| {
            update_config(&mut b);
            b.build()
        });

        if let Err(e) = result {
            error!("Unable to build the book");
            utils::log_backtrace(&e);
        }
    });

    Ok(())
}

fn remove_ignored_files(book_root: &Path, paths: &[PathBuf]) -> Vec<PathBuf> {
    if paths.is_empty() {
        return vec![];
    }

    match find_gitignore(book_root) {
        Some(gitignore_path) => {
            let (ignore, err) = Gitignore::new(&gitignore_path);
            if let Some(err) = err {
                warn!(
                    "error reading gitignore `{}`: {err}",
                    gitignore_path.display()
                );
            }
            filter_ignored_files(ignore, paths)
        }
        None => {
            // There is no .gitignore file.
            paths.iter().map(|path| path.to_path_buf()).collect()
        }
    }
}

fn find_gitignore(book_root: &Path) -> Option<PathBuf> {
    book_root
        .ancestors()
        .map(|p| p.join(".gitignore"))
        .find(|p| p.exists())
}

// Note: The usage of `canonicalize` may encounter occasional failures on the Windows platform, presenting a potential risk.
// For more details, refer to [Pull Request #2229](https://github.com/rust-lang/mdBook/pull/2229#discussion_r1408665981).
fn filter_ignored_files(ignore: Gitignore, paths: &[PathBuf]) -> Vec<PathBuf> {
    let ignore_root = ignore
        .path()
        .canonicalize()
        .expect("ignore root canonicalize error");

    paths
        .iter()
        .filter(|path| {
            let relative_path =
                diff_paths(&path, &ignore_root).expect("One of the paths should be an absolute");
            !ignore
                .matched_path_or_any_parents(&relative_path, relative_path.is_dir())
                .is_ignore()
        })
        .map(|path| path.to_path_buf())
        .collect()
}

/// Calls the closure when a book source file is changed, blocking indefinitely.
pub fn trigger_on_change<F>(book: &MDBook, closure: F)
where
    F: Fn(Vec<PathBuf>, &Path),
{
    use notify::RecursiveMode::*;

    // Create a channel to receive the events.
    let (tx, rx) = channel();

    let mut debouncer = match notify_debouncer_mini::new_debouncer(Duration::from_secs(1), tx) {
        Ok(d) => d,
        Err(e) => {
            error!("Error while trying to watch the files:\n\n\t{:?}", e);
            std::process::exit(1)
        }
    };
    let watcher = debouncer.watcher();

    // Add the source directory to the watcher
    if let Err(e) = watcher.watch(&book.source_dir(), Recursive) {
        error!("Error while watching {:?}:\n    {:?}", book.source_dir(), e);
        std::process::exit(1);
    };

    let _ = watcher.watch(&book.theme_dir(), Recursive);

    // Add the book.toml file to the watcher if it exists
    let _ = watcher.watch(&book.root.join("book.toml"), NonRecursive);

    for dir in &book.config.build.extra_watch_dirs {
        let path = book.root.join(dir);
        let canonical_path = path.canonicalize().unwrap_or_else(|e| {
            error!("Error while watching extra directory {path:?}:\n    {e}");
            std::process::exit(1);
        });

        if let Err(e) = watcher.watch(&canonical_path, Recursive) {
            error!(
                "Error while watching extra directory {:?}:\n    {:?}",
                canonical_path, e
            );
            std::process::exit(1);
        }
    }

    info!("Listening for changes...");

    loop {
        let first_event = rx.recv().unwrap();
        sleep(Duration::from_millis(50));
        let other_events = rx.try_iter();

        let all_events = std::iter::once(first_event).chain(other_events);

        let paths: Vec<_> = all_events
            .filter_map(|event| match event {
                Ok(events) => Some(events),
                Err(error) => {
                    log::warn!("error while watching for changes: {error}");
                    None
                }
            })
            .flatten()
            .map(|event| event.path)
            .collect();

        // If we are watching files outside the current repository (via extra-watch-dirs), then they are definitionally
        // ignored by gitignore. So we handle this case by including such files into the watched paths list.
        let any_external_paths = paths.iter().filter(|p| !p.starts_with(&book.root)).cloned();
        let mut paths = remove_ignored_files(&book.root, &paths[..]);
        paths.extend(any_external_paths);

        if !paths.is_empty() {
            closure(paths, &book.root);
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use ignore::gitignore::GitignoreBuilder;
    use std::env;

    #[test]
    fn test_filter_ignored_files() {
        let current_dir = env::current_dir().unwrap();

        let ignore = GitignoreBuilder::new(&current_dir)
            .add_line(None, "*.html")
            .unwrap()
            .build()
            .unwrap();
        let should_remain = current_dir.join("record.text");
        let should_filter = current_dir.join("index.html");

        let remain = filter_ignored_files(ignore, &[should_remain.clone(), should_filter]);
        assert_eq!(remain, vec![should_remain])
    }

    #[test]
    fn filter_ignored_files_should_handle_parent_dir() {
        let current_dir = env::current_dir().unwrap();

        let ignore = GitignoreBuilder::new(&current_dir)
            .add_line(None, "*.html")
            .unwrap()
            .build()
            .unwrap();

        let parent_dir = current_dir.join("..");
        let should_remain = parent_dir.join("record.text");
        let should_filter = parent_dir.join("index.html");

        let remain = filter_ignored_files(ignore, &[should_remain.clone(), should_filter]);
        assert_eq!(remain, vec![should_remain])
    }
}