Merge pull request #1900 from imachus/pr/ja-whitespace-fallback

Type: whitespace the primary font doesn't map takes the fallback face too (#1844)

crates/text/src/shape.rs

@@ -374,7 +374,10 @@ pub(crate) fn shape_range(
             // Digits are drawn in the style's numeral system: the font must cover that digit.
             let c = st.digits.map(c);
             let level = level_at(i);
-            let covered = c.is_whitespace() || c.is_control() || pmap.as_ref().is_none_or(|m| m.map(c).is_some());
+            // Whitespace the primary font doesn't map goes to the fallback face like any other
+            // character (#1844): an ideographic space set at zero width would remove an indent.
+            // What the layout handles itself (tab, line and paragraph breaks) stays.
+            let covered = c.is_control() || pmap.as_ref().is_none_or(|m| m.map(c).is_some());
             let face = if covered {
                 primary.clone()
             } else if let Some((_, f)) = cache.iter().find(|(k, _)| *k == c) {

crates/text/src/tests.rs

@@ -405,6 +405,26 @@ fn fallback_font_per_character() {
     assert_eq!(l.glyphs[2].font_id, primary.id());
 }
 
+/// A space the primary font doesn't map goes to the fallback face like any other character
+/// (#1844): an ideographic space in a face without U+3000 keeps its em, so an indent made with it
+/// isn't lost. A tab, which the layout handles itself, stays with the primary face. Needs a bundled
+/// face with U+3000 and あ (craft-fonts; skipped without it).
+#[test]
+fn whitespace_the_primary_font_lacks_takes_the_fallback_face() {
+    let primary = db().face("Source Sans 3", "Regular").unwrap();
+    assert!(!primary.covers('\u{3000}'));
+    if ['\u{3000}', 'あ'].iter().any(|&c| db().fallback_for(c, primary.id()).is_none()) {
+        eprintln!("skipped: built without craft-fonts (set CRAFT_FONTS_DIR to a craft-fonts checkout to run it)");
+        return;
+    }
+    let l = layout(db(), &point("あ\u{3000}あ", style(20.0)));
+    let width: f64 = l.glyphs.iter().map(|g| g.advance).sum();
+    assert!((width - 60.0).abs() < 0.01, "あ　あ sets at 3 em: {:?}", l.glyphs.iter().map(|g| g.advance).collect::<Vec<_>>());
+    assert_ne!(l.glyphs[1].font_id, primary.id());
+    let l = layout(db(), &point("a\tb", style(20.0)));
+    assert!(l.glyphs.iter().all(|g| g.font_id == primary.id()));
+}
+
 #[test]
 fn multiple_runs_and_styles() {
     let mut t = point("", style(10.0));