chore: refactor expression parser to avoid stack overflow issue

src/lexer/mod.rs

@@ -424,14 +424,28 @@ impl Lexer {
  state.source.next();
  DocStringKind::Nowdoc
  }
- _ => DocStringKind::Heredoc,
+ [b'"'] => {
+ state.source.next();
+ DocStringKind::Heredoc
+ }
+ [_, ..] => DocStringKind::Heredoc,
+ [] => {
+ return Err(SyntaxError::UnexpectedEndOfFile(state.source.span()));
+ }
  };
 
  // FIXME: Add support for nowdocs too by checking if a `'`
  // character is present before and after the identifier.
  let label: ByteString = match self.peek_identifier(state) {
  Some(_) => self.consume_identifier(state).into(),
- None => unreachable!(),
+ None => match state.source.current() {
+ Some(c) => {
+ return Err(SyntaxError::UnexpectedCharacter(*c, state.source.span()))
+ }
+ None => {
+ return Err(SyntaxError::UnexpectedEndOfFile(state.source.span()));
+ }
+ },
  };
 
  if doc_string_kind == DocStringKind::Nowdoc {
@@ -445,6 +459,8 @@ impl Lexer {
  ));
  }
  };
+ } else if let Some(b'"') = state.source.current() {
+ state.source.next();
  }
 
  if !matches!(state.source.current(), Some(b'\n')) {