Shell: Disallow non-bareword nodes as part of a heredoc key

Found by oss-fuzz:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=33854

Userland/Shell/Parser.cpp

@@ -1943,10 +1943,14 @@ RefPtr<AST::Node> Parser::parse_heredoc_initiation_record()
 
  // StringLiteral | bareword
  if (auto bareword = parse_bareword()) {
- if (bareword->is_syntax_error())
- syntax_error_node = bareword->syntax_error_node();
- else
- record.end = static_cast<AST::BarewordLiteral*>(bareword.ptr())->text();
+ if (!bareword->is_bareword()) {
+ syntax_error_node = create<AST::SyntaxError>(String::formatted("Expected a bareword or a quoted string, not {}", bareword->class_name()));
+ } else {
+ if (bareword->is_syntax_error())
+ syntax_error_node = bareword->syntax_error_node();
+ else
+ record.end = static_cast<AST::BarewordLiteral*>(bareword.ptr())->text();
+ }
 
  record.interpolate = true;
  } else if (peek() == '\'') {
@@ -1981,6 +1985,10 @@ bool Parser::parse_heredoc_entries()
  // Try to parse heredoc entries, as reverse recorded in the initiation records
  for (auto& record : m_heredoc_initiations) {
  auto rule_start = push_start();
+ if (m_rule_start_offsets.size() > max_allowed_nested_rule_depth) {
+ record.node->set_is_syntax_error(*create<AST::SyntaxError>(String::formatted("Expression nested too deep (max allowed is {})", max_allowed_nested_rule_depth)));
+ continue;
+ }
  bool found_key = false;
  if (!record.interpolate) {
  // Since no interpolation is allowed, just read lines until we hit the key