From 12129f01707a3389ef90a4c78a872e1c7897a752 Mon Sep 17 00:00:00 2001
From: Marmare314 <49279081+Marmare314@users.noreply.github.com>
Date: Mon, 24 Apr 2023 19:08:07 +0200
Subject: [PATCH] hint for unknown variable containing dash (#924)

---
 src/eval/scope.rs           | 14 ++++++++++++--
 tests/typ/compiler/hint.typ | 18 +++++++++++++++++-
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/eval/scope.rs b/src/eval/scope.rs
index 76633bf28..83d1703e9 100644
--- a/src/eval/scope.rs
+++ b/src/eval/scope.rs
@@ -42,7 +42,7 @@ impl<'a> Scopes<'a> {
             .chain(self.scopes.iter().rev())
             .chain(self.base.map(|base| base.global.scope()))
             .find_map(|scope| scope.get(var))
-            .ok_or_else(|| eco_format!("unknown variable: {}", var))
+            .ok_or_else(|| unknown_variable(var))
     }
 
     /// Try to access a variable immutably in math.
@@ -62,12 +62,22 @@ impl<'a> Scopes<'a> {
             .ok_or_else(|| {
                 match self.base.and_then(|base| base.global.scope().get(var)) {
                     Some(_) => eco_format!("cannot mutate a constant: {}", var),
-                    _ => eco_format!("unknown variable: {}", var),
+                    _ => unknown_variable(var),
                 }
             })?
     }
 }
 
+/// The error message when a variable is not found.
+#[cold]
+fn unknown_variable(var: &str) -> EcoString {
+    if var.contains('-') {
+        eco_format!("unknown variable: {} – if you meant to use subtraction, try adding spaces around the minus sign.", var)
+    } else {
+        eco_format!("unknown variable: {}", var)
+    }
+}
+
 /// A map from binding names to values.
 #[derive(Default, Clone, Hash)]
 pub struct Scope(BTreeMap<EcoString, Slot>, bool);
diff --git a/tests/typ/compiler/hint.typ b/tests/typ/compiler/hint.typ
index 4fd25abb5..881354438 100644
--- a/tests/typ/compiler/hint.typ
+++ b/tests/typ/compiler/hint.typ
@@ -3,4 +3,20 @@
 
 ---
 // Error: 1:17-1:19 expected length, found integer: a length needs a unit – did you mean 12pt?
-#set text(size: 12)
\ No newline at end of file
+#set text(size: 12)
+
+---
+#{
+  let a = 2
+  a = 1-a
+  a = a -1
+
+  // Error: 7-10 unknown variable: a-1 – if you meant to use subtraction, try adding spaces around the minus sign.
+  a = a-1
+}
+
+---
+#{
+  // Error: 3-6 unknown variable: a-1 – if you meant to use subtraction, try adding spaces around the minus sign.
+  a-1 = 2
+}