handle quoted strings in variable-exists

src/builtin/meta.rs

@@ -83,8 +83,10 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
         "variable-exists".to_owned(),
         Box::new(|args, scope| {
             max_args!(args, 1);
-            let value = arg!(args, 0, "name");
-            Ok(Value::bool(scope.var_exists(&value.to_string())))
+            match arg!(args, 0, "name") {
+                Value::Ident(s, _) => Ok(Value::bool(scope.var_exists(&s))),
+                v => Err(format!("$name: {} is not a string.", v).into()),
+            }
         }),
     );
     f.insert(

tests/meta.rs

@@ -244,6 +244,15 @@ test!(
     "$a: red; a {\n  color: variable-exists($name: a)\n}\n",
     "a {\n  color: true;\n}\n"
 );
+test!(
+    variable_exists_quoted,
+    "$a: red; a {\n  color: variable-exists('a')\n}\n",
+    "a {\n  color: true;\n}\n"
+);
+error!(
+    variable_exists_not_string,
+    "a {\n  color: variable-exists(12px)\n}\n", "Error: $name: 12px is not a string."
+);
 test!(
     mixin_does_exist,
     "@mixin a{} a {\n  color: mixin-exists(a)\n}\n",