Add complex-scripts feature for CJK and Southeast Asian line/word breaking

CHANGELOG.md

@@ -16,6 +16,7 @@ This release has an [MSRV] of 1.88.
 
 #### Parley
 
+- `complex-scripts` Cargo feature to enable dictionary-based line and word breaking for complex scripts (CJK, Thai, Khmer, Lao, Myanmar). When disabled, the lightweight segmenter is used (no change in default behavior).
 - `PlainEditor`, `Layout`, `LayoutAccessibility`, and `Generation` now implement `Debug`. ([#615][] by [@NandishwarSingh][])
   Note: The `Layout` implementation provides a compact summary by default; the alternate form (`{:#?}`) formats the full underlying data.
 

parley/Cargo.toml

@@ -23,6 +23,9 @@ libm = ["fontique/libm", "peniko/libm", "skrifa/libm", "dep:core_maths"]
 # Enables support for system font backends
 system = ["std", "fontique/system"]
 accesskit = ["dep:accesskit"]
+# Enables dictionary-based line and word breaking for complex scripts (CJK, Thai, Khmer, Lao, Myanmar).
+# When disabled, a lightweight segmenter is used that falls back to character-level breaks for those scripts.
+complex-scripts = []
 
 [dependencies]
 skrifa = { workspace = true }

parley/src/analysis/mod.rs

@@ -43,32 +43,33 @@ impl AnalysisDataSources {
 
     #[inline(always)]
     fn word_segmenter(&self) -> WordSegmenterBorrowed<'static> {
-        const { WordSegmenter::new_for_non_complex_scripts(WordBreakInvariantOptions::default()) }
+        #[cfg(feature = "complex-scripts")]
+        {
+            WordSegmenter::new_dictionary(WordBreakInvariantOptions::default())
+        }
+        #[cfg(not(feature = "complex-scripts"))]
+        {
+            const { WordSegmenter::new_for_non_complex_scripts(WordBreakInvariantOptions::default()) }
+        }
     }
 
     #[inline(always)]
     fn line_segmenter(&self, word_break_strength: WordBreak) -> LineSegmenterBorrowed<'static> {
         match word_break_strength {
             WordBreak::Normal => {
-                const {
-                    let mut opt = LineBreakOptions::default();
-                    opt.word_option = Some(LineBreakWordOption::Normal);
-                    LineSegmenter::new_for_non_complex_scripts(opt)
-                }
+                let mut opt = LineBreakOptions::default();
+                opt.word_option = Some(LineBreakWordOption::Normal);
+                line_segmenter_impl(opt)
             }
             WordBreak::BreakAll => {
-                const {
-                    let mut opt = LineBreakOptions::default();
-                    opt.word_option = Some(LineBreakWordOption::BreakAll);
-                    LineSegmenter::new_for_non_complex_scripts(opt)
-                }
+                let mut opt = LineBreakOptions::default();
+                opt.word_option = Some(LineBreakWordOption::BreakAll);
+                line_segmenter_impl(opt)
             }
             WordBreak::KeepAll => {
-                const {
-                    let mut opt = LineBreakOptions::default();
-                    opt.word_option = Some(LineBreakWordOption::KeepAll);
-                    LineSegmenter::new_for_non_complex_scripts(opt)
-                }
+                let mut opt = LineBreakOptions::default();
+                opt.word_option = Some(LineBreakWordOption::KeepAll);
+                line_segmenter_impl(opt)
             }
         }
     }
@@ -94,6 +95,18 @@ impl AnalysisDataSources {
     }
 }
 
+#[cfg(feature = "complex-scripts")]
+#[inline(always)]
+fn line_segmenter_impl(opt: LineBreakOptions<'_>) -> LineSegmenterBorrowed<'static> {
+    LineSegmenter::new_dictionary(opt)
+}
+
+#[cfg(not(feature = "complex-scripts"))]
+#[inline(always)]
+fn line_segmenter_impl(opt: LineBreakOptions<'_>) -> LineSegmenterBorrowed<'static> {
+    LineSegmenter::new_for_non_complex_scripts(opt)
+}
+
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub(crate) struct CharInfo {
     /// The line/word breaking boundary classification of this character.