HACK: somewhat handle unicode escapes

src/lexer.rs

@@ -17,6 +17,7 @@ pub(crate) struct Lexer<'a> {
     tokens: Vec<Token>,
     buf: Peekable<Chars<'a>>,
     pos: Pos,
+    should_emit_backslash: usize,
 }
 
 impl<'a> Iterator for Lexer<'a> {
@@ -36,6 +37,13 @@ impl<'a> Iterator for Lexer<'a> {
                 TokenKind::Whitespace(Whitespace::$whitespace)
             }};
         }
+        if self.should_emit_backslash > 0 {
+            self.should_emit_backslash -= 1;
+            return Some(Token {
+                kind: TokenKind::Symbol(Symbol::BackSlash),
+                pos: self.pos,
+            });
+        }
         let kind: TokenKind = match self.buf.peek().unwrap_or(&'\0') {
             'a'..='z' | 'A'..='Z' | '_' => self.lex_ident(),
             '-' => {
@@ -107,7 +115,7 @@ impl<'a> Iterator for Lexer<'a> {
                 }
             }
             '?' => symbol!(self, QuestionMark),
-            '\\' => symbol!(self, BackSlash),
+            '\\' => self.lex_back_slash().0,
             '~' => symbol!(self, Tilde),
             '\'' => symbol!(self, SingleQuote),
             '"' => symbol!(self, DoubleQuote),
@@ -158,6 +166,7 @@ impl<'a> Lexer<'a> {
             tokens: Vec::with_capacity(buf.len()),
             buf: buf.chars().peekable(),
             pos: Pos::new(),
+            should_emit_backslash: 0,
         }
     }
 
@@ -209,6 +218,51 @@ impl<'a> Lexer<'a> {
         }
     }
 
+    fn lex_back_slash(&mut self) -> (TokenKind, bool) {
+        self.buf.next();
+        self.pos.next_char();
+        if self.buf.peek() == Some(&'\\') {
+            self.buf.next();
+            self.pos.next_char();
+            self.should_emit_backslash = 1;
+            (TokenKind::Symbol(Symbol::BackSlash), true)
+        } else {
+            let mut n = String::new();
+            while let Some(c) = self.buf.peek() {
+                if !c.is_ascii_hexdigit() || n.len() > 6 {
+                    break;
+                }
+                n.push(*c);
+                self.buf.next();
+                self.pos.next_char();
+            }
+
+            if n.is_empty() {
+                return (TokenKind::Symbol(Symbol::BackSlash), false);
+            }
+
+            let mut string = std::char::from_u32(u32::from_str_radix(&n, 16).unwrap())
+                .unwrap()
+                .to_string();
+            self.devour_whitespace();
+            if let TokenKind::Ident(s) = self.lex_ident() {
+                string.push_str(&s);
+            }
+            (TokenKind::Ident(string), false)
+        }
+    }
+
+    fn devour_whitespace(&mut self) {
+        while let Some(c) = self.buf.peek() {
+            if c.is_ascii_whitespace() {
+                self.buf.next();
+                self.pos.next_char();
+                continue;
+            }
+            break;
+        }
+    }
+
     fn lex_forward_slash(&mut self) -> TokenKind {
         self.buf.next();
         self.pos.next_char();
@@ -331,18 +385,30 @@ impl<'a> Lexer<'a> {
         }
     }
 
-    // TODO: handle weird characters that *are* ascii
-    // e.g. how do we handle `color: ;`
     fn lex_ident(&mut self) -> TokenKind {
         let mut string = String::with_capacity(99);
         while let Some(c) = self.buf.peek() {
-            // we know that the first char is alphabetic from peeking
-            if !c.is_alphanumeric() && c != &'-' && c != &'_' && c.is_ascii() {
+            if !c.is_alphanumeric() && c != &'-' && c != &'_' && c != &'\\' && c.is_ascii() {
                 break;
             }
             if !c.is_ascii() {
                 IS_UTF8.store(true, Ordering::Relaxed);
             }
+            if c == &'\\' {
+                match self.lex_back_slash() {
+                    (TokenKind::Ident(s), _) => string.push_str(&s),
+                    (TokenKind::Symbol(..), true) => {
+                        self.should_emit_backslash = 2;
+                        break;
+                    }
+                    (TokenKind::Symbol(..), false) => {
+                        self.should_emit_backslash = 1;
+                        break;
+                    }
+                    _ => unreachable!(),
+                }
+                continue;
+            }
             let tok = self
                 .buf
                 .next()

src/utils.rs

@@ -160,6 +160,19 @@ pub(crate) fn flatten_ident<I: Iterator<Item = Token>>(
                 toks.next();
                 s.push_str(n)
             }
+            TokenKind::Symbol(Symbol::BackSlash) => {
+                s.push('\\');
+                toks.next();
+                if let Some(tok) = toks.next() {
+                    match tok.kind {
+                        TokenKind::Symbol(Symbol::Plus) => s.push('+'),
+                        TokenKind::Symbol(Symbol::BackSlash) => s.push('\\'),
+                        _ => todo!("value after \\"),
+                    }
+                } else {
+                    todo!()
+                }
+            }
             _ => break,
         }
     }

src/value/parse.rs

@@ -294,6 +294,23 @@ impl Value {
             TokenKind::Keyword(Keyword::To(s)) => Ok(Value::Ident(s, QuoteKind::None)),
             TokenKind::AtRule(_) => Err("expected \";\".".into()),
             TokenKind::Error(e) => return Err(e),
+            TokenKind::Symbol(Symbol::BackSlash) => {
+                if let Some(tok) = toks.next() {
+                    match tok.kind {
+                        TokenKind::Symbol(Symbol::Plus) => Ok(Value::Ident(
+                            "\\+".to_string() + &flatten_ident(toks, scope, super_selector)?,
+                            QuoteKind::None,
+                        )),
+                        TokenKind::Symbol(Symbol::BackSlash) => Ok(Value::Ident(
+                            "\\\\".to_string() + &flatten_ident(toks, scope, super_selector)?,
+                            QuoteKind::None,
+                        )),
+                        _ => todo!("value after \\"),
+                    }
+                } else {
+                    todo!()
+                }
+            }
             TokenKind::Op(Op::Plus) | TokenKind::Symbol(Symbol::Plus) => {
                 devour_whitespace_or_comment(toks);
                 let v = Self::_from_tokens(toks, scope, super_selector)?;

tests/misc.rs

@@ -66,3 +66,19 @@ test!(
     "a {\n  color: red😁\n}\n",
     "@charset \"UTF-8\";\na {\n  color: red😁;\n}\n"
 );
+test!(
+    escape_recognized_as_at_rule,
+    "@\\69 f true {\n  a {\n    b: c;\n  }\n}\n",
+    "a {\n  b: c;\n}\n"
+);
+test!(
+    escape_in_middle,
+    "a {\n  color: b\\6cue;\n}\n",
+    "a {\n  color: blue;\n}\n"
+);
+test!(
+    escape_at_end,
+    "a {\n  color: blu\\65;\n}\n",
+    "a {\n  color: blue;\n}\n"
+);
+test!(double_escape_is_preserved, "a {\n  color: r\\\\65;\n}\n");