Text: a drop cap in a document font aligns its left edge

A drop cap set in one of the document's own fonts measures its side
bearing in that font, through the document's font scope, so Align Left
Edge puts its ink at the indent.

crates/compose/src/tests.rs

@@ -2728,3 +2728,29 @@ fn vertical_lines_fit_the_em_box() {
         assert!((l.baseline - col.y0 - ascent).abs() < 1e-9, "{family}: {} {}", l.baseline, col.y0);
     }
 }
+
+/// A drop cap set in one of the document's own fonts measures its side bearing in that font.
+#[test]
+fn drop_cap_in_a_document_font_aligns_its_left_edge() {
+    use designcraft_geom::Shape as _;
+    const FAMILY: &str = "DocFont Drop Cap";
+    let text = format!("Once {LOREM}");
+    let mut chars: Vec<char> = text.chars().collect();
+    chars.sort_unstable();
+    chars.dedup();
+    let folder = std::env::temp_dir().join(format!("dc-compose-dropcap-docfont-{}", std::process::id()));
+    std::fs::create_dir_all(&folder).unwrap();
+    std::fs::write(folder.join("dropcap.ttf"), designcraft_fonts::testing::font_with_glyph(FAMILY, &chars, 'O').unwrap()).unwrap();
+    let scope = designcraft_fonts::FontDb::global().load_document_fonts(&folder).scope;
+    let para = ParaAttrs { left_indent: Some(10.0), ..drop_cap(2, 1) };
+    let (mut d, sid, _) = doc_with(&text, Rect::new(0.0, 0.0, 300.0, 1000.0), para);
+    d.font_scope = scope;
+    d.story_mut(sid).unwrap().format_chars(0..text.len(), |f| f.over.font_family = Some(FAMILY.into()));
+    let cs = compose_story(&d, sid, &ComposeOptions::default());
+    let dc = &all_lines(&cs)[0].glyphs[0];
+    assert_eq!(dc.face.family, FAMILY);
+    let ink_left = dc.x + designcraft_fonts::FontDb::global().outline(dc.face.get(), dc.gid).bounding_box().x0 * dc.sx;
+    assert!(ink_left - dc.x > 0.5, "the O has a visible side bearing");
+    assert!((ink_left - 10.0).abs() < 1e-6, "ink at {ink_left}");
+    let _ = std::fs::remove_dir_all(&folder);
+}