Parse multi-character numbers consistently in math (#5996)

Co-authored-by: Laurenz <laurmaedje@gmail.com>

crates/typst-syntax/src/parser.rs

@@ -271,11 +271,9 @@ fn math_expr_prec(p: &mut Parser, min_prec: usize, stop: SyntaxKind) {
         }
 
         SyntaxKind::Text | SyntaxKind::MathText | SyntaxKind::MathShorthand => {
-            continuable = !p.at(SyntaxKind::MathShorthand)
-                && matches!(
-                    math_class(p.current_text()),
-                    None | Some(MathClass::Alphabetic)
-                );
+            // `a(b)/c` parses as `(a(b))/c` if `a` is continuable.
+            continuable = math_class(p.current_text()) == Some(MathClass::Alphabetic)
+                || p.current_text().chars().all(char::is_alphabetic);
             if !maybe_delimited(p) {
                 p.eat();
             }

tests/suite/math/frac.typ

@@ -37,8 +37,8 @@ $ 1/2/3 = (1/2)/3 = 1/(2/3) $
 // Test precedence.
 $ a_1/b_2, 1/f(x), zeta(x)/2, "foo"[|x|]/2 \
   1.2/3.7, 2.3^3.4 \
-  🏳️‍🌈[x]/2, f [x]/2, phi [x]/2, 🏳️‍🌈 [x]/2 \
-  +[x]/2, 1(x)/2, 2[x]/2 \
+  f [x]/2, phi [x]/2 \
+  +[x]/2, 1(x)/2, 2[x]/2, 🏳️‍🌈[x]/2 \
   (a)b/2, b(a)[b]/2 \
   n!/2, 5!/2, n !/2, 1/n!, 1/5! $
 

tests/suite/math/syntax.typ

@@ -28,6 +28,10 @@ $ dot \ dots \ ast \ tilde \ star $
 $floor(phi.alt.)$
 $floor(phi.alt. )$
 
+--- issue-4828-math-number-multi-char ---
+// Numbers should parse the same regardless of number of characters.
+$1/2(x)$ vs. $1/10(x)$
+
 --- math-unclosed ---
 // Error: 1-2 unclosed delimiter
 $a