fix: fix LuaLaTeX rendering of left-to-right text in right-to-left bo…

…oks (#144) Fixes errors like: ``` Error producing PDF. ! Undefined control sequence. l.279 ...اوقات زبان Rust را با C و \LR ```
max-heller · Jan 12, 2025 · d506526 · d506526
1 parent b6334b2
commit d506526
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diff --git a/scripts/install-ci-deps b/scripts/install-ci-deps
@@ -17,7 +17,7 @@ export PATH="$PWD/pandoc-3.6.1/bin:$PATH"
 sudo apt-get install -y librsvg2-bin
 
 # TeX Live and fonts
-sudo apt-get install -y texlive texlive-luatex texlive-lang-cjk texlive-fonts-extra fonts-font-awesome fonts-noto fonts-noto-cjk fonts-noto-color-emoji
+sudo apt-get install -y texlive texlive-luatex texlive-lang-cjk texlive-lang-arabic texlive-fonts-extra fonts-font-awesome fonts-noto fonts-noto-cjk fonts-noto-color-emoji
 
 # mdBook preprocessors needed by example books
 cargo install mdbook-i18n-helpers --locked
diff --git a/src/lib.rs b/src/lib.rs
@@ -2090,6 +2090,39 @@ include-in-header = ["file-in-root"]
         ");
     }
 
+    #[test]
+    #[ignore]
+    fn right_to_left_fonts_lualatex() {
+        let cfg = r#"
+[book]
+language = "fa"
+
+[output.pandoc.profile.pdf]
+output-file = "book.pdf"
+pdf-engine = "lualatex"
+
+[output.pandoc.profile.pdf.variables]
+mainfont = "Noto Naskh Arabic"
+mainfontfallback = [
+  "NotoSerif:",
+]
+        "#;
+        let output = MDBook::init()
+            .mdbook_config(cfg.parse().unwrap())
+            .chapter(Chapter::new("", "<span dir=ltr>C++</span>", "chapter.md"))
+            .build();
+        insta::assert_snapshot!(output, @r#"
+        ├─ log output
+        │  INFO mdbook::book: Running the pandoc backend    
+        │  INFO mdbook_pandoc::pandoc::renderer: Running pandoc    
+        │  INFO mdbook_pandoc::pandoc::renderer: Wrote output to book/pdf/book.pdf    
+        ├─ pdf/book.pdf
+        │ <INVALID UTF8>
+        ├─ pdf/src/chapter.md
+        │ [Para [Span ("", [], [("dir", "ltr")]) [Str "C++"]]]
+        "#);
+    }
+
     static BOOKS: Lazy<PathBuf> = Lazy::new(|| Path::new(env!("CARGO_MANIFEST_DIR")).join("books"));
 
     #[test]

diff --git a/src/pandoc/renderer.rs b/src/pandoc/renderer.rs
@@ -8,6 +8,7 @@ use std::{
 };
 
 use anyhow::Context as _;
+use mdbook::config::TextDirection;
 use normpath::PathExt;
 use tempfile::NamedTempFile;
 
@@ -170,6 +171,20 @@ impl Renderer {
                     additional_variables.push(("include-before", include_before))
                 }
 
+                if ctx.mdbook_cfg.book.realized_text_direction() == TextDirection::RightToLeft {
+                    // Without this, LuaTeX errors on left-to-right text because the \LR command isn't defined, e.g.:
+                    //   Error producing PDF.
+                    //   ! Undefined control sequence.
+                    //   l.279 ...اوقات زبان Rust را با C و \LR
+                    // (see https://github.com/google/comprehensive-rust/pull/2531#issuecomment-2567445055)
+                    // Using luabidi was suggested in
+                    // https://github.com/jgm/pandoc/issues/8460#issuecomment-1344881107
+                    additional_variables.push((
+                        "header-includes",
+                        r"\ifLuaTeX\usepackage{luabidi}\fi".into(),
+                    ));
+                }
+
                 let include_packages = packages
                     .needed()
                     .map(|package| format!(r"\usepackage{{{}}}", package.name()))