Update mdBook manual to have information about translations

guide/src/en/cli/init.md

@@ -14,13 +14,19 @@ up for you:
 ```bash
 book-test/
 ├── book
+├── book.toml
 └── src
-    ├── chapter_1.md
-    └── SUMMARY.md
+    └── en
+        ├── chapter_1.md
+        └── SUMMARY.md
 ```
 
-- The `src` directory is where you write your book in markdown. It contains all
-  the source files, configuration files, etc.
+- The `src` directory is where you write your book in Markdown. It contains all
+  the source files for each translation of your book. By default, a directory
+  for the English translation is created, `src/en`.
+
+- The `book.toml` file holds configuration about how your book gets rendered.
+  See the [configuration](../format/config.md) section for more details.
 
 - The `book` directory is where your book is rendered. All the output is ready
   to be uploaded to a server to be seen by your audience.

guide/src/en/for_developers/preprocessors.md

@@ -56,7 +56,7 @@ be adapted for other preprocessors.
 ```rust
 // nop-preprocessors.rs
 
-{{#include ../../../examples/nop-preprocessor.rs}}
+{{#include ../../../../examples/nop-preprocessor.rs}}
 ```
 </details>
 

guide/src/en/format/configuration/README.md

@@ -4,9 +4,11 @@ This section details the configuration options available in the ***book.toml***:
 - **[General]** configuration including the `book`, `rust`, `build` sections
 - **[Preprocessor]** configuration for default and custom book preprocessors
 - **[Renderer]** configuration for the HTML, Markdown and custom renderers
+- **[Translations]** configuration for books written in more than one language
 - **[Environment Variable]** configuration for overriding configuration options in your environment
 
 [General]: general.md
 [Preprocessor]: preprocessors.md
 [Renderer]: renderers.md
-[Environment Variable]: environment-variables.md
+[Translations]: translations.md
+[Environment Variable]: environment-variables.md

guide/src/en/format/configuration/translations.md

@@ -0,0 +1,86 @@
+## Translations
+
+It's possible to write your book in more than one language and bundle all of its
+translations into a single output folder, with the ability for readers to switch
+between each one in the rendered output. The available languages for your book
+are defined in the `[language]` table:
+
+```toml
+[language.en]
+name = "English"
+
+[language.ja]
+name = "日本語"
+title = "本のサンプル"
+description = "この本は実例です。"
+authors = ["Ruin0x11"]
+```
+
+Each language must have a human-readable `name` defined. Also, if the
+`[language]` table is defined, you must define `book.language` to be a key of
+this table, which will indicate the language whose files will be used for
+fallbacks if a page is missing in a translation.
+
+The `title` and `description` fields, if defined, will override the ones set in
+the `[book]` section. This way you can translate the book's title and
+description. `authors` provides a list of this translation's authors.
+
+After defining a new language like `[language.ja]`, add a new subdirectory
+`src/ja` and create your `SUMMARY.md` and other files there.
+
+> **Note:** Whether or not the `[language]` table is defined changes the format
+> of the `src` directory that mdBook expects to see. If there is no `[language]`
+> table, mdBook will treat the `src` directory as a single translation of the
+> book, with `SUMMARY.md` at the root:
+>
+> ```
+> ├── book.toml
+> └── src
+>     ├── chapter
+>     │   ├── 1.md
+>     │   ├── 2.md
+>     │   └── README.md
+>     ├── README.md
+>     └── SUMMARY.md
+> ```
+> 
+> If the `[language]` table is defined, mdBook will instead expect to find
+> subdirectories under `src` named after the keys in the table:
+>
+> ```
+> ├── book.toml
+> └── src
+>     ├── en
+>     │   ├── chapter
+>     │   │   ├── 1.md
+>     │   │   ├── 2.md
+>     │   │   └── README.md
+>     │   ├── README.md
+>     │   └── SUMMARY.md
+>     └── ja
+>         ├── chapter
+>         │   ├── 1.md
+>         │   ├── 2.md
+>         │   └── README.md
+>         ├── README.md
+>         └── SUMMARY.md
+> ```
+
+If the `[language]` table is used, you can pass the `-l <language id>` argument
+to commands like `mdbook build` to build the book for only a single language. In
+this example, `<language id>` can be `en` or `ja`.
+
+Some extra notes on translations:
+
+- In a translation's `SUMMARY.md` or inside Markdown files, you can link to
+  pages, images or other files that don't exist in the current translation, but
+  do exist in the default translation. This is so you can have a fallback in
+  case new pages get added in the default language that haven't been translated
+  yet.
+- Each translation can have its own `SUMMARY.md` with differing content from
+  other translations. Even if the translation's summary goes out of sync with
+  the default language, the links will continue to work so long as the pages
+  exist in either translation.
+- Each translation can have its own pages listed in `SUMMARY.md` that don't
+  exist in the default translation at all, in case extra information specific to
+  that language is needed.

guide/src/en/misc/contributors.md

@@ -20,5 +20,6 @@ shout-out to them!
 - Vivek Akupatni ([apatniv](https://github.com/apatniv))
 - Eric Huss ([ehuss](https://github.com/ehuss))
 - Josh Rotenberg ([joshrotenberg](https://github.com/joshrotenberg))
+- [Ruin0x11](https://github.com/Ruin0x11)
 
 If you feel you're missing from this list, feel free to add yourself in a PR.

src/config.rs

@@ -1020,6 +1020,7 @@ mod tests {
         assert_eq!(got.rust, rust_should_be);
         assert_eq!(got.html_config().unwrap(), html_should_be);
         assert_eq!(got.language, language_should_be);
+        assert_eq!(got.default_language(), Some(String::from("ja")));
     }
 
     #[test]
@@ -1369,7 +1370,18 @@ mod tests {
 
     #[test]
     #[should_panic(expected = "Invalid configuration file")]
-    fn validate_config_default_language_must_exist_in_languages_table() {
+    fn book_language_without_languages_table() {
+        let src = r#"
+        [book]
+        language = "en"
+        "#;
+
+        Config::from_str(src).unwrap();
+    }
+
+    #[test]
+    #[should_panic(expected = "Invalid configuration file")]
+    fn default_language_must_exist_in_languages_table() {
         let src = r#"
         [language.ja]
         name = "日本語"

src/utils/mod.rs

@@ -10,7 +10,7 @@ use pulldown_cmark::{html, CodeBlockKind, CowStr, Event, Options, Parser, Tag};
 
 use std::borrow::Cow;
 use std::fmt::Write;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 pub use self::string::{
     take_anchored_lines, take_lines, take_rustdoc_include_anchored_lines,
@@ -99,9 +99,9 @@ pub fn id_from_content(content: &str) -> String {
     normalize_id(trimmed)
 }
 
-fn rewrite_if_missing(
+fn rewrite_if_missing<P: AsRef<Path>>(
     fixed_link: &mut String,
-    path_to_dest: &PathBuf,
+    path_to_dest: P,
     dest: &str,
     src_dir: &PathBuf,
     language: &str,
@@ -114,15 +114,15 @@ fn rewrite_if_missing(
     // if the file exists.
     let mut path_on_disk = src_dir.clone();
     path_on_disk.push(language);
-    path_on_disk.push(path_to_dest);
+    path_on_disk.push(path_to_dest.as_ref());
     path_on_disk.push(dest);
 
     debug!("Checking if {} exists", path_on_disk.display());
     if !path_on_disk.exists() {
         // Now see if the file exists in the fallback language directory (like "src/en").
         let mut fallback_path = src_dir.clone();
         fallback_path.push(fallback_language);
-        fallback_path.push(path_to_dest);
+        fallback_path.push(path_to_dest.as_ref());
         fallback_path.push(dest);
 
         debug!(
@@ -133,7 +133,7 @@ fn rewrite_if_missing(
             // We can fall back to this link. Get enough parent directories to
             // reach the root source directory, append the fallback language
             // directory to it, the prepend the whole thing to the link.
-            let mut relative_path = PathBuf::from(path_to_dest);
+            let mut relative_path = PathBuf::from(path_to_dest.as_ref());
             relative_path.push(dest);
 
             let mut path_to_fallback_src = fs::path_to_root(&relative_path);
@@ -158,7 +158,6 @@ fn fix<'a>(dest: CowStr<'a>, ctx: Option<&RenderMarkdownContext>) -> CowStr<'a>
                 if base.ends_with(".md") {
                     base.replace_range(base.len() - 3.., ".html");
                 }
-                info!("{:?} {:?}", base, dest);
                 return format!("{}{}", base, dest).into();
             } else {
                 return dest;
@@ -173,14 +172,16 @@ fn fix<'a>(dest: CowStr<'a>, ctx: Option<&RenderMarkdownContext>) -> CowStr<'a>
         let mut fixed_link = String::new();
 
         if let Some(ctx) = ctx {
+            let base = ctx.path.parent().expect("path can't be empty");
+
             // If the book is multilingual, check if the file actually
             // exists, and if not rewrite the link to the fallback
             // language's page.
             if let Some(language) = &ctx.language {
                 if let Some(fallback_language) = &ctx.fallback_language {
                     rewrite_if_missing(
                         &mut fixed_link,
-                        &ctx.path,
+                        &base,
                         &dest,
                         &ctx.src_dir,
                         &language,
@@ -190,13 +191,7 @@ fn fix<'a>(dest: CowStr<'a>, ctx: Option<&RenderMarkdownContext>) -> CowStr<'a>
             }
 
             if ctx.prepend_parent {
-                let base = ctx
-                    .path
-                    .parent()
-                    .expect("path can't be empty")
-                    .to_str()
-                    .expect("utf-8 paths only");
-
+                let base = base.to_str().expect("utf-8 paths only");
                 if !base.is_empty() {
                     write!(fixed_link, "{}/", base).unwrap();
                 }
@@ -562,27 +557,22 @@ more text with spaces
                 );
             };
 
-            test("../b/summary.md", "a", true, "../b/summary.html");
-            test("../b/summary.md", "a", false, "../../en/../b/summary.html");
-            test("../c/summary.md", "a/b", true, "../c/summary.html");
+            test("../b/summary.md", "a.md", true, "../b/summary.html");
             test(
-                "../c/summary.md",
-                "a/b",
+                "../b/summary.md",
+                "a.md",
                 false,
-                "../../../en/../c/summary.html",
+                "../../en/../b/summary.html",
             );
+            test("../c/summary.md", "a/b.md", true, "../c/summary.html");
             test(
-                "#translations",
-                "config.md",
-                true,
-                "#translations",
-            );
-            test(
-                "#translations",
-                "config.md",
+                "../c/summary.md",
+                "a/b.md",
                 false,
-                "#translations",
+                "../../../en/../c/summary.html",
             );
+            test("#translations", "config.md", true, "#translations");
+            test("#translations", "config.md", false, "#translations");
         }
     }
 

tests/localized_book/src/en/README.md

@@ -1,3 +1,5 @@
 # Localized Book
 
 This is a test of the book localization features.
+
+Select a language from the dropdown to see a translation of the current page.

tests/localized_book/src/ja/SUMMARY.md

@@ -5,5 +5,5 @@
     - [第一節](chapter/1.md)
     - [第二節](chapter/2.md)
 - [Untranslated Page](untranslated-page.md)
-- [日本語専用のページ](translation-local-page.md)
 - [内部リンクの入れ替え](inline-link-fallbacks.md)
+- [日本語専用のページ](translation-local-page.md)

tests/localized_book/src/ja/inline-link-fallbacks.md

@@ -8,7 +8,7 @@ If inline link substitution works, then an image should appear below, sourced fr
 
 Here is an [inline link](translation-local-page.md) to an existing page in this translation.
 
-Here is an [inline link](missing-summary-chapter.md) to a page missing from this translation's SUMMARY.md. It should have been modified to point to the page in the English version of the book.
+Here is an [inline link](missing-summary-chapter.md) to a page missing from this translation's `SUMMARY.md`. It should have been modified to point to the page in the English version of the book.
 
 Also, here is an [inline link](blah.md) to a page missing from both translations. It should point to this language's 404 page.