Fix bug in math.frac layout code (#5177)

crates/typst/src/math/frac.rs

@@ -130,8 +130,9 @@ fn layout(
     )?;
 
     let around = FRAC_AROUND.at(font_size);
-    let num_gap = (shift_up - axis - num.descent()).max(num_min + thickness / 2.0);
-    let denom_gap = (shift_down + axis - denom.ascent()).max(denom_min + thickness / 2.0);
+    let num_gap = (shift_up - (axis + thickness / 2.0) - num.descent()).max(num_min);
+    let denom_gap =
+        (shift_down + (axis - thickness / 2.0) - denom.ascent()).max(denom_min);
 
     let line_width = num.width().max(denom.width());
     let width = line_width + 2.0 * around;

tests/suite/math/frac.typ

@@ -41,3 +41,7 @@ $ a_1/b_2, 1/f(x), zeta(x)/2, "foo"[|x|]/2 \
   +[x]/2, 1(x)/2, 2[x]/2 \
   (a)b/2, b(a)[b]/2 \
   n!/2, 5!/2, n !/2, 1/n!, 1/5! $
+
+--- math-frac-gap ---
+// Test that the gap above and below the fraction rule is correct.
+$ sqrt(n^(2/3)) $

tests/suite/visualize/gradient.typ

@@ -497,7 +497,7 @@ $ nabla dot bold(E) = frac(rho, epsilon_0) $
 #show math.equation: set text(fill: gradient.linear(..color.map.rainbow))
 #show math.equation: box
 
-$ x_"1,2" = frac(-b +- sqrt(b^2 - 4 a c), 2 a) $
+$ x_"1,2" = frac(-b plus.minus sqrt(b^2 - 4 a c), 2 a) $
 
 --- gradient-math-mat ---
 // Test on matrix
@@ -529,7 +529,7 @@ $ A = mat(
   7, 8, 9
 ) $
 
-$ x_"1,2" = frac(-b +- sqrt(b^2 - 4 a c), 2 a) $
+$ x_"1,2" = frac(-b plus.minus sqrt(b^2 - 4 a c), 2 a) $
 
 --- gradient-math-misc ---
 // Test miscellaneous