Show rules for symbols (fixes #1130) (#1175)

src/model/styles.rs

@@ -472,8 +472,10 @@ pub struct ShowableSelector(pub Selector);
 
 impl Cast for ShowableSelector {
     fn is(value: &Value) -> bool {
-        matches!(value, Value::Str(_) | Value::Label(_) | Value::Func(_))
-            || value.type_name() == "regular expression"
+        matches!(
+            value,
+            Value::Symbol(_) | Value::Str(_) | Value::Label(_) | Value::Func(_)
+        ) || value.type_name() == "regular expression"
             || value.type_name() == "selector"
     }
 
@@ -510,6 +512,7 @@ impl Cast for ShowableSelector {
             CastInfo::Type("label"),
             CastInfo::Type("string"),
             CastInfo::Type("regular expression"),
+            CastInfo::Type("symbol"),
             CastInfo::Type("selector"),
         ])
     }

tests/typ/compiler/show-node.typ

@@ -96,7 +96,7 @@ Hey
 = Heading
 
 ---
-// Error: 7-10 expected function, label, string, regular expression, or selector, found color
+// Error: 7-10 expected function, label, string, regular expression, symbol, or selector, found color
 #show red: []
 
 ---

tests/typ/math/style.typ

@@ -28,3 +28,8 @@ $text(#red, "time"^2) + sqrt("place")$
 // Test different font.
 #show math.equation: set text(font: "Fira Math")
 $ v := vec(1 + 2, 2 - 4, sqrt(3), arrow(x)) + 1 $
+
+---
+// Test using rules for symbols
+#show sym.tack: it => $#h(1em) it #h(1em)$
+$ a tack b $