allow escaped ! in selectors

src/parse/mod.rs

@@ -364,6 +364,12 @@ impl<'a> Parser<'a> {
                     found_curly = true;
                     break;
                 }
+                '\\' => {
+                    string.push('\\');
+                    if let Some(Token { kind, .. }) = self.toks.next() {
+                        string.push(kind);
+                    }
+                }
                 '!' => {
                     if peek_ident_no_interpolation(self.toks, false, self.span_before)?.node
                         == "optional"

src/utils/peek_until.rs

@@ -133,7 +133,8 @@ pub(crate) fn peek_escape(toks: &mut PeekMoreIterator<IntoIter<Token>>) -> SassR
             toks.peek_forward(1);
         }
     } else {
-        value = toks.peek_forward(1).unwrap().kind as u32;
+        value = first.kind as u32;
+        toks.advance_cursor();
     }
 
     let c = std::char::from_u32(value).ok_or(("Invalid escape sequence.", span))?;

tests/error.rs

@@ -245,3 +245,4 @@ error!(
     "a {foo: {bar: red", "Error: Expected identifier."
 );
 error!(toplevel_nullbyte, "\u{0}", "Error: expected selector.");
+error!(double_escaped_bang_at_toplevel, "\\!\\!", "Error: expected \"{\".");

tests/selectors.rs

@@ -350,6 +350,11 @@ test!(
     "ul li#foo {\n  foo: bar;\n}\n"
 );
 test!(escaped_space, "a\\ b {\n  color: foo;\n}\n");
+test!(
+    escaped_bang,
+    "\\! {\n  color: red;\n}\n",
+    "\\! {\n  color: red;\n}\n"
+);
 test!(
     multiple_consecutive_immediate_child,
     "> > foo {\n  color: foo;\n}\n"