The preprocessor trait now returns a modified book instead of editing in place

examples/de-emphasize.rs

@@ -14,45 +14,7 @@ use std::env::{args, args_os};
 use std::ffi::OsString;
 use std::process;
 
-struct Deemphasize;
-
-impl Preprocessor for Deemphasize {
-    fn name(&self) -> &str {
-        "md-links-to-html-links"
-    }
-
-    fn run(&self, _ctx: &PreprocessorContext, book: &mut Book) -> Result<()> {
-        eprintln!("Running '{}' preprocessor", self.name());
-        let mut res: Option<_> = None;
-        let mut num_removed_items = 0;
-        book.for_each_mut(|item: &mut BookItem| {
-            if let Some(Err(_)) = res {
-                return;
-            }
-            if let BookItem::Chapter(ref mut chapter) = *item {
-                eprintln!("{}: processing chapter '{}'", self.name(), chapter.name);
-                res = Some(
-                    match Deemphasize::remove_emphasis(&mut num_removed_items, chapter) {
-                        Ok(md) => {
-                            chapter.content = md;
-                            Ok(())
-                        }
-                        Err(err) => Err(err),
-                    },
-                );
-            }
-        });
-        eprintln!(
-            "{}: removed {} events from markdown stream.",
-            self.name(),
-            num_removed_items
-        );
-        match res {
-            Some(res) => res,
-            None => Ok(()),
-        }
-    }
-}
+const NAME: &str = "md-links-to-html-links";
 
 fn do_it(book: OsString) -> Result<()> {
     let mut book = MDBook::load(book)?;
@@ -71,24 +33,66 @@ fn main() {
     }
 }
 
-impl Deemphasize {
-    fn remove_emphasis(num_removed_items: &mut i32, 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)))
+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))
+    })
+}

src/book/mod.rs

@@ -149,23 +149,35 @@ impl MDBook {
     pub fn build(&self) -> Result<()> {
         info!("Book building has started");
 
-        let mut preprocessed_book = self.book.clone();
-        let preprocess_ctx = PreprocessorContext::new(self.root.clone(), self.config.clone());
-
-        for preprocessor in &self.preprocessors {
-            debug!("Running the {} preprocessor.", preprocessor.name());
-            preprocessor.run(&preprocess_ctx, &mut preprocessed_book)?;
-        }
-
         for renderer in &self.renderers {
-            info!("Running the {} backend", renderer.name());
-            self.run_renderer(&preprocessed_book, renderer.as_ref())?;
+            self.execute_build_process(&**renderer)?;
         }
 
         Ok(())
     }
 
-    fn run_renderer(&self, preprocessed_book: &Book, renderer: &Renderer) -> Result<()> {
+    fn execute_build_process(&self, renderer: &Renderer) -> Result<()> {
+        let mut preprocessed_book = self.book.clone();
+        let preprocess_ctx =
+            PreprocessorContext::new(self.root.clone(), self.config.clone());
+
+        for preprocessor in &self.preprocessors {
+            debug!("Running the {} preprocessor.", preprocessor.name());
+            preprocessed_book =
+                preprocessor.run(&preprocess_ctx, preprocessed_book)?;
+        }
+
+        info!("Running the {} backend", renderer.name());
+        self.render(&preprocessed_book, renderer)?;
+
+        Ok(())
+    }
+
+    fn render(
+        &self,
+        preprocessed_book: &Book,
+        renderer: &Renderer,
+    ) -> Result<()> {
         let name = renderer.name();
         let build_dir = self.build_dir_for(name);
         if build_dir.exists() {
@@ -217,11 +229,11 @@ impl MDBook {
 
         let preprocess_context = PreprocessorContext::new(self.root.clone(), self.config.clone());
 
-        LinkPreprocessor::new().run(&preprocess_context, &mut self.book)?;
+        let book = LinkPreprocessor::new().run(&preprocess_context, self.book.clone())?;
         // Index Preprocessor is disabled so that chapter paths continue to point to the
         // actual markdown files.
 
-        for item in self.iter() {
+        for item in book.iter() {
             if let BookItem::Chapter(ref ch) = *item {
                 if !ch.path.as_os_str().is_empty() {
                     let path = self.source_dir().join(&ch.path);

src/preprocess/index.rs

@@ -22,7 +22,7 @@ impl Preprocessor for IndexPreprocessor {
         "index"
     }
 
-    fn run(&self, ctx: &PreprocessorContext, book: &mut Book) -> Result<()> {
+    fn run(&self, ctx: &PreprocessorContext, mut book: Book) -> Result<Book> {
         let source_dir = ctx.root.join(&ctx.config.book.src);
         book.for_each_mut(|section: &mut BookItem| {
             if let BookItem::Chapter(ref mut ch) = *section {
@@ -37,7 +37,7 @@ impl Preprocessor for IndexPreprocessor {
             }
         });
 
-        Ok(())
+        Ok(book)
     }
 }
 

src/preprocess/links.rs

@@ -27,7 +27,7 @@ impl Preprocessor for LinkPreprocessor {
         "links"
     }
 
-    fn run(&self, ctx: &PreprocessorContext, book: &mut Book) -> Result<()> {
+    fn run(&self, ctx: &PreprocessorContext, mut book: Book) -> Result<Book> {
         let src_dir = ctx.root.join(&ctx.config.book.src);
 
         book.for_each_mut(|section: &mut BookItem| {
@@ -43,7 +43,7 @@ impl Preprocessor for LinkPreprocessor {
             }
         });
 
-        Ok(())
+        Ok(book)
     }
 }
 

src/preprocess/mod.rs

@@ -36,5 +36,5 @@ pub trait Preprocessor {
 
     /// Run this `Preprocessor`, allowing it to update the book before it is
     /// given to a renderer.
-    fn run(&self, ctx: &PreprocessorContext, book: &mut Book) -> Result<()>;
+    fn run(&self, ctx: &PreprocessorContext, book: Book) -> Result<Book>;
 }

tests/testing.rs

@@ -39,9 +39,9 @@ fn mdbook_runs_preprocessors() {
             "dummy"
         }
 
-        fn run(&self, _ctx: &PreprocessorContext, _book: &mut Book) -> Result<()> {
+        fn run(&self, _ctx: &PreprocessorContext, book: Book) -> Result<Book> {
             *self.0.lock().unwrap() = true;
-            Ok(())
+            Ok(book)
         }
     }