handle control characters at start of selector

src/lib.rs

@@ -397,6 +397,9 @@ impl<'a> StyleSheetParser<'a> {
                         "Base-level rules cannot contain the parent-selector-referencing character '&'.".into(),
                     )
                 }
+                c if c.is_control() => {
+                    return Err("expected selector.".into());
+                }
                 _ => match dbg!(self.lexer.next()) {
                     Some(Token { pos, .. }) => self.error(pos, "unexpected toplevel token"),
                     _ => unsafe { std::hint::unreachable_unchecked() },

src/selector.rs

@@ -331,6 +331,9 @@ impl<'a> SelectorParser<'a> {
                         self.super_selector,
                     )?)
                 }
+                c if c.is_control() => {
+                    return Err("expected selector.".into());
+                }
                 _ => todo!("unimplemented selector"),
             };
         }

tests/error.rs

@@ -44,3 +44,11 @@ error!(
     symbol_after_hash,
     "a {color: bar + #}ar;}", "Error: Expected identifier."
 );
+error!(
+    control_character_starts_selector_toplevel,
+    "l {color: foo;}", "Error: expected selector."
+);
+error!(
+    control_character_starts_selector_inner,
+    "a{l {color: foo;}}", "Error: expected selector."
+);