disallow standalone @else

src/atrule/kind.rs

@@ -1,3 +1,9 @@
+use std::convert::TryFrom;
+
+use codemap::Spanned;
+
+use crate::error::SassError;
+
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum AtRuleKind {
     // SASS specific @rules
@@ -57,9 +63,10 @@ pub enum AtRuleKind {
     Unknown(String),
 }
 
-impl From<&str> for AtRuleKind {
-    fn from(c: &str) -> Self {
-        match c.to_ascii_lowercase().as_str() {
+impl TryFrom<&Spanned<String>> for AtRuleKind {
+    type Error = SassError;
+    fn try_from(c: &Spanned<String>) -> Result<Self, SassError> {
+        Ok(match c.node.to_ascii_lowercase().as_str() {
             "use" => Self::Use,
             "forward" => Self::Forward,
             "import" => Self::Import,
@@ -81,7 +88,9 @@ impl From<&str> for AtRuleKind {
             "keyframes" => Self::Keyframes,
             "content" => Self::Content,
             "media" => Self::Media,
+            "else" => return Err(("This at-rule is not allowed here.", c.span).into()),
+            "" => return Err(("Expected identifier.", c.span).into()),
             s => Self::Unknown(s.to_owned()),
-        }
+        })
     }
 }

src/lib.rs

@@ -82,6 +82,7 @@ grass input.scss
 #![cfg_attr(feature = "nightly", feature(track_caller))]
 #![cfg_attr(feature = "profiling", inline(never))]
 
+use std::convert::TryFrom;
 use std::iter::Iterator;
 
 use codemap::{Span, Spanned};
@@ -337,10 +338,10 @@ pub(crate) fn eat_expr<I: Iterator<Item = Token>>(
             }
             '@' => {
                 let span = toks.next().unwrap().pos();
-                let Spanned { node: ident, span } = eat_ident(toks, scope, super_selector, span)?;
+                let rule = eat_ident(toks, scope, super_selector, span)?;
                 devour_whitespace(toks);
                 let rule = AtRule::from_tokens(
-                    AtRuleKind::from(ident.as_str()),
+                    AtRuleKind::try_from(&rule)?,
                     span,
                     toks,
                     scope,

src/stylesheet.rs

@@ -1,3 +1,4 @@
+use std::convert::TryFrom;
 use std::fs;
 use std::iter::Iterator;
 use std::path::Path;
@@ -226,20 +227,14 @@ impl<'a> StyleSheetParser<'a> {
                 }
                 '@' => {
                     let span_before = self.lexer.next().unwrap().pos();
-                    let Spanned {
-                        node: at_rule_kind,
-                        span,
-                    } = eat_ident(self.lexer, &Scope::new(), &Selector::new(), span_before)?;
-                    if at_rule_kind.is_empty() {
-                        return Err(("Expected identifier.", span).into());
-                    }
-                    match AtRuleKind::from(at_rule_kind.as_str()) {
+                    let rule = eat_ident(self.lexer, &Scope::new(), &Selector::new(), span_before)?;
+                    match AtRuleKind::try_from(&rule)? {
                         AtRuleKind::Include => rules.extend(eat_include(
                             self.lexer,
                             &Scope::new(),
                             &Selector::new(),
                             None,
-                            span,
+                            rule.span,
                         )?),
                         AtRuleKind::Import => {
                             devour_whitespace(self.lexer);
@@ -259,7 +254,7 @@ impl<'a> StyleSheetParser<'a> {
                                         )?
                                         .node
                                         .unquote()
-                                        .to_css_string(span)?,
+                                        .to_css_string(rule.span)?,
                                     );
                                 }
                                 _ => return Err(("Expected string.", next.pos()).into()),
@@ -282,7 +277,7 @@ impl<'a> StyleSheetParser<'a> {
                         v => {
                             let rule = AtRule::from_tokens(
                                 v,
-                                span,
+                                rule.span,
                                 self.lexer,
                                 &mut Scope::new(),
                                 &Selector::new(),

tests/error.rs

@@ -200,4 +200,11 @@ error!(value_after_style, "a {}a", "Error: expected \"{\".");
 test!(whitespace_after_style, "a {}\t\n ", "");
 test!(toplevel_semicolon, ";", "");
 test!(toplevel_semicolon_after_style, "a {};", "");
-error!(nothing_after_hash_in_interpolated_ident_body, "a {color: foo#", "Error: Expected identifier.");
+error!(
+    nothing_after_hash_in_interpolated_ident_body,
+    "a {color: foo#", "Error: Expected identifier."
+);
+error!(
+    at_else_alone,
+    "@else {}", "Error: This at-rule is not allowed here."
+);