Add support for watching additional directories

Author: willcrichton

src/cmd/watch.rs

@@ -146,6 +146,10 @@ where
     // 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 _ = watcher.watch(dir, Recursive);
+    }
+
     info!("Listening for changes...");
 
     loop {

src/config.rs

@@ -437,6 +437,8 @@ pub struct BuildConfig {
     /// Should the default preprocessors always be used when they are
     /// compatible with the renderer?
     pub use_default_preprocessors: bool,
+    /// Extra directories to trigger rebuild when watching/serving
+    pub extra_watch_dirs: Vec<PathBuf>,
 }
 
 impl Default for BuildConfig {
@@ -445,6 +447,7 @@ impl Default for BuildConfig {
             build_dir: PathBuf::from("book"),
             create_missing: true,
             use_default_preprocessors: true,
+            extra_watch_dirs: Vec::new(),
         }
     }
 }