Improve unknown variable diagnostics (#4858)

crates/typst/src/foundations/scope.rs

@@ -73,7 +73,12 @@ impl<'a> Scopes<'a> {
                     None => None,
                 })
             })
-            .ok_or_else(|| unknown_variable(var))
+            .ok_or_else(|| {
+                unknown_variable_math(
+                    var,
+                    self.base.is_some_and(|base| base.global.scope().get(var).is_some()),
+                )
+            })
     }
 
     /// Try to access a variable mutably.
@@ -109,13 +114,28 @@ fn cannot_mutate_constant(var: &str) -> HintedString {
 fn unknown_variable(var: &str) -> HintedString {
     let mut res = HintedString::new(eco_format!("unknown variable: {}", var));
 
+    if var.contains('-') {
+        res.hint(eco_format!(
+            "if you meant to use subtraction, try adding spaces around the minus sign{}: `{}`",
+            if var.matches('-').count() > 1 { "s" } else { "" },
+            var.replace('-', " - ")
+        ));
+    }
+
+    res
+}
+
+#[cold]
+fn unknown_variable_math(var: &str, in_global: bool) -> HintedString {
+    let mut res = HintedString::new(eco_format!("unknown variable: {}", var));
+
     if matches!(var, "none" | "auto" | "false" | "true") {
         res.hint(eco_format!(
-            "if you meant to use a literal, try adding a hash before it"
+            "if you meant to use a literal, try adding a hash before it: `#{var}`",
         ));
-    } else if var.contains('-') {
+    } else if in_global {
         res.hint(eco_format!(
-            "if you meant to use subtraction, try adding spaces around the minus sign",
+            "`{var}` is not available directly in math, try adding a hash before it: `#{var}`",
         ));
     }
 

tests/suite/math/call.typ

@@ -95,3 +95,8 @@ $ mat(
    ,1, ;
    , ,1;
 ) $
+
+--- issue-2885-math-var-only-in-global ---
+// Error: 7-10 unknown variable: rgb
+// Hint: 7-10 `rgb` is not available directly in math, try adding a hash before it: `#rgb`
+$text(rgb(0, 0, 0), "foo")$

tests/suite/scripting/ops.typ

@@ -414,7 +414,7 @@
 --- ops-assign-unknown-var-lhs ---
 #{
   // Error: 3-6 unknown variable: a-1
-  // Hint: 3-6 if you meant to use subtraction, try adding spaces around the minus sign
+  // Hint: 3-6 if you meant to use subtraction, try adding spaces around the minus sign: `a - 1`
   a-1 = 2
 }
 
@@ -425,7 +425,7 @@
   a = a -1
 
   // Error: 7-10 unknown variable: a-1
-  // Hint: 7-10 if you meant to use subtraction, try adding spaces around the minus sign
+  // Hint: 7-10 if you meant to use subtraction, try adding spaces around the minus sign: `a - 1`
   a = a-1
 }