Make under/overlines behave the same as accents in attach base (#4695)

crates/typst/src/math/underover.rs

@@ -67,7 +67,7 @@ fn layout_underoverline(
     span: Span,
     position: Position,
 ) -> SourceResult<()> {
-    let (extra_height, content, line_pos, content_pos, baseline, bar_height);
+    let (extra_height, content, line_pos, content_pos, baseline, bar_height, line_adjust);
     match position {
         Position::Under => {
             let sep = scaled!(ctx, styles, underbar_extra_descender);
@@ -79,7 +79,8 @@ fn layout_underoverline(
 
             line_pos = Point::with_y(content.height() + gap + bar_height / 2.0);
             content_pos = Point::zero();
-            baseline = content.ascent()
+            baseline = content.ascent();
+            line_adjust = -content.italics_correction();
         }
         Position::Over => {
             let sep = scaled!(ctx, styles, overbar_extra_ascender);
@@ -93,21 +94,25 @@ fn layout_underoverline(
             line_pos = Point::with_y(sep + bar_height / 2.0);
             content_pos = Point::with_y(extra_height);
             baseline = content.ascent() + extra_height;
+            line_adjust = Abs::zero();
         }
     }
 
     let width = content.width();
     let height = content.height() + extra_height;
     let size = Size::new(width, height);
+    let line_width = width + line_adjust;
 
     let content_class = content.class();
+    let content_is_text_like = content.is_text_like();
+    let content_italics_correction = content.italics_correction();
     let mut frame = Frame::soft(size);
     frame.set_baseline(baseline);
     frame.push_frame(content_pos, content.into_frame());
     frame.push(
         line_pos,
         FrameItem::Shape(
-            Geometry::Line(Point::with_x(width)).stroked(FixedStroke {
+            Geometry::Line(Point::with_x(line_width)).stroked(FixedStroke {
                 paint: TextElem::fill_in(styles).as_decoration(),
                 thickness: bar_height,
                 ..FixedStroke::default()
@@ -116,7 +121,12 @@ fn layout_underoverline(
         ),
     );
 
-    ctx.push(FrameFragment::new(ctx, styles, frame).with_class(content_class));
+    ctx.push(
+        FrameFragment::new(ctx, styles, frame)
+            .with_class(content_class)
+            .with_text_like(content_is_text_like)
+            .with_italics_correction(content_italics_correction),
+    );
 
     Ok(())
 }

tests/suite/math/underover.typ

@@ -33,3 +33,15 @@ $ undershell(
   1 + overshell(2 + ..., x + y),
   "all stuff"
 ) $
+
+--- math-underover-line-subscript ---
+// Test effect of lines on subscripts.
+$A_2 != overline(A)_2 != underline(A)_2 != underline(overline(A))_2 \
+ V_y != overline(V)_y != underline(V)_y != underline(overline(V))_y \
+ W_l != overline(W)_l != underline(W)_l != underline(overline(W))_l$
+
+--- math-underover-line-superscript ---
+// Test effect of lines on superscripts.
+$J^b != overline(J)^b != underline(J)^b != underline(overline(J))^b \
+ K^3 != overline(K)^3 != underline(K)^3 != underline(overline(K))^3 \
+ T^i != overline(T)^i != underline(T)^i != underline(overline(T))^i$