Support OpenType writing script (#1697)

3 files changed, 43 insertions, 6 deletions

diff --git a/crates/typst-library/src/layout/par.rs b/crates/typst-library/src/layout/par.rs
index fe86f62a..6d1b653f 100644
--- a/crates/typst-library/src/layout/par.rs
+++ b/crates/typst-library/src/layout/par.rs
@@ -750,6 +750,7 @@ fn shape_range<'a>(
     spans: &SpanMapper,
     styles: StyleChain<'a>,
 ) {
+    let script = TextElem::script_in(styles);
     let lang = TextElem::lang_in(styles);
     let region = TextElem::region_in(styles);
     let mut process = |range: Range, level: BidiLevel| {
@@ -763,25 +764,31 @@ fn shape_range<'a>(
     let mut prev_script = Script::Unknown;
     let mut cursor = range.start;
 
-    // Group by embedding level and script.
+    // Group by embedding level and script.  If the text's script is explicitly
+    // set (rather than inferred from the glpyhs), we keep the script at an
+    // unchanging `Script::Unknown` so that only level changes cause breaks.
     for i in range.clone() {
         if !bidi.text.is_char_boundary(i) {
             continue;
         }
 
         let level = bidi.levels[i];
-        let script =
-            bidi.text[i..].chars().next().map_or(Script::Unknown, |c| c.script());
+        let curr_script = match script {
+            Smart::Auto => {
+                bidi.text[i..].chars().next().map_or(Script::Unknown, |c| c.script())
+            }
+            Smart::Custom(_) => Script::Unknown,
+        };
 
-        if level != prev_level || !is_compatible(script, prev_script) {
+        if level != prev_level || !is_compatible(curr_script, prev_script) {
             if cursor < i {
                 process(cursor..i, prev_level);
             }
             cursor = i;
             prev_level = level;
-            prev_script = script;
+            prev_script = curr_script;
         } else if is_generic_script(prev_script) {
-            prev_script = script;
+            prev_script = curr_script;
         }
     }
 
diff --git a/crates/typst-library/src/text/mod.rs b/crates/typst-library/src/text/mod.rs
index f7c15c29..6cfcb7c7 100644
--- a/crates/typst-library/src/text/mod.rs
+++ b/crates/typst-library/src/text/mod.rs
@@ -265,6 +265,31 @@ pub struct TextElem {
     #[default(BottomEdge::Metric(BottomEdgeMetric::Baseline))]
     pub bottom_edge: BottomEdge,
 
+    /// The OpenType writing script setting.
+    ///
+    /// The combination of `{script}` and `{lang}` determine how
+    /// font features, such as glyph substitution, are implemented.
+    /// Frequently the value is a modified (all-lowercase) ISO 15924 script identifier, and
+    /// the `math` writing script is used for features appropriate
+    /// for mathematical symbols.
+    ///
+    /// When set to `{auto}`, the default and recommended setting,
+    /// an appropriate script is chosen for each block of characters
+    /// sharing a common Unicode script property.
+    ///
+    /// ```example
+    /// #let scedilla = [Ş]
+    /// #set text(font: "Linux Libertine", size: 20pt)
+    /// #scedilla // S with a cedilla
+    ///
+    /// #set text(script: "latn", lang: "ro")
+    /// #scedilla // S with a subscript comma
+    ///
+    /// #set text(script: "grek", lang: "ro")
+    /// #scedilla // S with a cedilla
+    /// ```
+    pub script: Smart<WritingScript>,
+
     /// An [ISO 639-1/2/3 language code.](https://en.wikipedia.org/wiki/ISO_639)
     ///
     /// Setting the correct language affects various parts of Typst:
diff --git a/crates/typst-library/src/text/shaping.rs b/crates/typst-library/src/text/shaping.rs
index 3ccac635..53289e26 100644
--- a/crates/typst-library/src/text/shaping.rs
+++ b/crates/typst-library/src/text/shaping.rs
@@ -634,6 +634,11 @@ fn shape_segment(
     let mut buffer = UnicodeBuffer::new();
     buffer.push_str(text);
     buffer.set_language(language(ctx.styles));
+    if let Some(script) = TextElem::script_in(ctx.styles).as_custom().and_then(|script| {
+        rustybuzz::Script::from_iso15924_tag(Tag::from_bytes(script.as_bytes()))
+    }) {
+        buffer.set_script(script)
+    }
     buffer.set_direction(match ctx.dir {
         Dir::LTR => rustybuzz::Direction::LeftToRight,
         Dir::RTL => rustybuzz::Direction::RightToLeft,