Add an iterator over chapters

This adds the `Book::chapters` iterator (and `for_each_chapter_mut`) to
iterate over non-draft chapters. This is a common pattern I keep
encountering, and I figure it might simplify things. It runs a little
risk that callers may not be properly handling every item type, but I
think it should be ok.

crates/mdbook-core/src/book.rs

@@ -46,6 +46,14 @@ impl Book {
         }
     }
 
+    /// A depth-first iterator over each [`Chapter`], skipping draft chapters.
+    pub fn chapters(&self) -> impl Iterator<Item = &Chapter> {
+        self.iter().filter_map(|item| match item {
+            BookItem::Chapter(ch) if !ch.is_draft_chapter() => Some(ch),
+            _ => None,
+        })
+    }
+
     /// Recursively apply a closure to each item in the book, allowing you to
     /// mutate them.
     ///
@@ -61,6 +69,26 @@ impl Book {
         for_each_mut(&mut func, &mut self.items);
     }
 
+    /// Recursively apply a closure to each non-draft chapter in the book,
+    /// allowing you to mutate them.
+    pub fn for_each_chapter_mut<F>(&mut self, mut func: F)
+    where
+        F: FnMut(&mut Chapter),
+    {
+        for_each_mut(
+            &mut |item| {
+                let BookItem::Chapter(ch) = item else {
+                    return;
+                };
+                if ch.is_draft_chapter() {
+                    return;
+                }
+                func(ch)
+            },
+            &mut self.items,
+        );
+    }
+
     /// Append a `BookItem` to the `Book`.
     pub fn push_item<I: Into<BookItem>>(&mut self, item: I) -> &mut Self {
         self.items.push(item.into());

crates/mdbook-driver/src/builtin_renderers/markdown_renderer.rs

@@ -1,5 +1,4 @@
 use anyhow::{Context, Result};
-use mdbook_core::book::BookItem;
 use mdbook_core::utils;
 use mdbook_renderer::{RenderContext, Renderer};
 use std::fs;
@@ -33,16 +32,12 @@ impl Renderer for MarkdownRenderer {
         }
 
         trace!("markdown render");
-        for item in book.iter() {
+        for ch in book.chapters() {
-            if let BookItem::Chapter(ref ch) = *item {
+            utils::fs::write_file(
-                if !ch.is_draft_chapter() {
+                &ctx.destination,
-                    utils::fs::write_file(
+                ch.path.as_ref().expect("Checked path exists before"),
-                        &ctx.destination,
+                ch.content.as_bytes(),
-                        ch.path.as_ref().expect("Checked path exists before"),
+            )?;
-                        ch.content.as_bytes(),
-                    )?;
-                }
-            }
         }
 
         fs::create_dir_all(destination)

crates/mdbook-html/src/html_handlebars/hbs_renderer.rs

@@ -459,13 +459,7 @@ impl Renderer for HtmlHandlebars {
             utils::fs::write_file(destination, "CNAME", format!("{cname}\n").as_bytes())?;
         }
 
-        let chapters: Vec<_> = book
+        let chapters: Vec<_> = book.chapters().collect();
-            .iter()
-            .filter_map(|item| match item {
-                BookItem::Chapter(ch) if !ch.is_draft_chapter() => Some(ch),
-                _ => None,
-            })
-            .collect();
         for (i, ch) in chapters.iter().enumerate() {
             let previous = (i != 0).then(|| chapters[i - 1]);
             let next = (i != chapters.len() - 1).then(|| chapters[i + 1]);

crates/mdbook-html/src/html_handlebars/search.rs

@@ -2,7 +2,7 @@ use super::static_files::StaticFiles;
 use crate::theme::searcher;
 use anyhow::{Context, Result, bail};
 use elasticlunr::{Index, IndexBuilder};
-use mdbook_core::book::{Book, BookItem, Chapter};
+use mdbook_core::book::{Book, Chapter};
 use mdbook_core::config::{Search, SearchChapterSettings};
 use mdbook_core::utils;
 use mdbook_markdown::HtmlRenderOptions;
@@ -43,11 +43,7 @@ pub(super) fn create_files(
     let chapter_configs = sort_search_config(&search_config.chapter);
     validate_chapter_config(&chapter_configs, book)?;
 
-    for item in book.iter() {
+    for chapter in book.chapters() {
-        let chapter = match item {
-            BookItem::Chapter(ch) if !ch.is_draft_chapter() => ch,
-            _ => continue,
-        };
         if let Some(path) = settings_path(chapter) {
             let chapter_settings = get_chapter_settings(&chapter_configs, path);
             if !chapter_settings.enable.unwrap_or(true) {
@@ -349,11 +345,8 @@ fn validate_chapter_config(
 ) -> Result<()> {
     for (path, _) in chapter_configs {
         let found = book
-            .iter()
+            .chapters()
-            .filter_map(|item| match item {
+            .filter_map(|ch| settings_path(ch))
-                BookItem::Chapter(ch) if !ch.is_draft_chapter() => settings_path(ch),
-                _ => None,
-            })
             .any(|source_path| source_path.starts_with(path));
         if !found {
             bail!(

examples/remove-emphasis/mdbook-remove-emphasis/src/main.rs

@@ -1,7 +1,7 @@
 //! This is a demonstration of an mdBook preprocessor which parses markdown
 //! and removes any instances of emphasis.
 
-use mdbook_preprocessor::book::{Book, BookItem, Chapter};
+use mdbook_preprocessor::book::{Book, Chapter};
 use mdbook_preprocessor::errors::Result;
 use mdbook_preprocessor::{Preprocessor, PreprocessorContext};
 use pulldown_cmark::{Event, Parser, Tag, TagEnd};
@@ -36,17 +36,9 @@ impl Preprocessor for RemoveEmphasis {
 
     fn run(&self, _ctx: &PreprocessorContext, mut book: Book) -> Result<Book> {
         let mut total = 0;
-        book.for_each_mut(|item| {
+        book.for_each_chapter_mut(|ch| match remove_emphasis(&mut total, ch) {
-            let BookItem::Chapter(ch) = item else {
+            Ok(s) => ch.content = s,
-                return;
+            Err(e) => eprintln!("failed to process chapter: {e:?}"),
-            };
-            if ch.is_draft_chapter() {
-                return;
-            }
-            match remove_emphasis(&mut total, ch) {
-                Ok(s) => ch.content = s,
-                Err(e) => eprintln!("failed to process chapter: {e:?}"),
-            }
         });
         eprintln!("removed {total} emphasis");
         Ok(book)

guide/guide-helper/src/lib.rs

@@ -1,6 +1,6 @@
 //! Preprocessor for the mdBook guide.
 
-use mdbook_preprocessor::book::{Book, BookItem};
+use mdbook_preprocessor::book::Book;
 use mdbook_preprocessor::errors::Result;
 use mdbook_preprocessor::{Preprocessor, PreprocessorContext};
 use semver::{Version, VersionReq};
@@ -53,13 +53,7 @@ fn insert_version(book: &mut Book) {
     let manifest: toml::Value = toml::from_str(&manifest_contents).unwrap();
     let version = manifest["package"]["version"].as_str().unwrap();
     const MARKER: &str = "{{ mdbook-version }}";
-    book.for_each_mut(|item| {
+    book.for_each_chapter_mut(|ch| {
-        let BookItem::Chapter(ch) = item else {
-            return;
-        };
-        if ch.is_draft_chapter() {
-            return;
-        }
         if ch.content.contains(MARKER) {
             ch.content = ch.content.replace(MARKER, version);
         }