resolve issue with @ at-root

CHANGELOG.md

@@ -1,3 +1,6 @@
+# 0.9.1
+ - fix issue in which `@at-root` would panic when placed after a ruleset
+
 # 0.9.0
 
 This release is focused on setting up the groundwork for implementing `@extend` as well

src/output.rs

@@ -114,7 +114,8 @@ impl Css {
             Stmt::UnknownAtRule {
                 params, name, body, ..
             } => vec![Toplevel::UnknownAtRule { params, name, body }],
-            Stmt::Return(..) | Stmt::AtRoot { .. } => unreachable!(),
+            Stmt::Return(..) => unreachable!("@return: {:?}", stmt),
+            Stmt::AtRoot { .. } => unreachable!("@at-root: {:?}", stmt),
         })
     }
 

src/parse/mod.rs

@@ -283,6 +283,7 @@ impl<'a> Parser<'a> {
                         let body = self.parse_stmt()?;
                         self.scopes.pop();
                         self.super_selectors.pop();
+                        self.at_root = self.super_selectors.is_empty();
                         stmts.push(Stmt::RuleSet {
                             selector,
                             body,

tests/at-root.rs

@@ -63,3 +63,8 @@ test!(
     "test {\n  @at-root {\n    #{&} {\n      foo {\n        bar: baz;\n      }\n    }\n  }\n}\n",
     "test foo {\n  bar: baz;\n}\n"
 );
+test!(
+    style_before_at_root,
+    "a {}\n\n@at-root {\n    @-ms-viewport { width: device-width; }\n}\n",
+    "@-ms-viewport {\n  width: device-width;\n}\n"
+);