swc-project/swc · warning · swc_html_parser::error::Error

End of file seen without seeing a doctype first, expected "<

Error message

End of file seen without seeing a doctype first, expected "<!DOCTYPE html>"

What it means

Initial insertion mode, 'anything else' branch (crates/swc_html_parser/src/parser/mod.rs:1432): the token stream reached EOF before any doctype (and before any other content), with iframe_srcdoc false. Parse error; the document is set to quirks mode. An empty or whitespace/comment-only input is the classic trigger.

Source

Thrown at crates/swc_html_parser/src/parser/mod.rs:1432

                                    self.errors.push(Error::new(
                                        token_and_info.span,
                                        ErrorKind::StartTagWithoutDoctype,
                                    ));
                                }
                                Token::EndTag { .. } => {
                                    self.errors.push(Error::new(
                                        token_and_info.span,
                                        ErrorKind::EndTagSeenWithoutDoctype,
                                    ));
                                }
                                Token::Character { .. } => {
                                    self.errors.push(Error::new(
                                        token_and_info.span,
                                        ErrorKind::NonSpaceCharacterWithoutDoctype,
                                    ));
                                }
                                Token::Eof => {
                                    self.errors.push(Error::new(
                                        token_and_info.span,
                                        ErrorKind::EofWithoutDoctype,
                                    ));
                                }
                                _ => {
                                    unreachable!();
                                }
                            }

                            self.set_document_mode(DocumentMode::Quirks);
                        }

                        self.insertion_mode = InsertionMode::BeforeHtml;
                        self.process_token(token_and_info, None)?;
                    }
                }
            }
            // The "before html" insertion mode

View on GitHub (pinned to 5176682b65)

Solutions

  1. Guard against empty input before parsing and skip/short-circuit
  2. Set ParserConfig { iframe_srcdoc: true, .. } if empty srcdoc documents are legitimate in your flow
  3. Treat EofWithoutDoctype on empty input as an upstream data problem: fetch/validate the source

Example fix

// before
let fm = cm.new_source_file(file.into(), String::new());
let doc = parse_file_as_document(&fm, config, &mut errors)?; // EofWithoutDoctype + quirks

// after
if html.trim().is_empty() {
    return Ok(empty_document());
}
let fm = cm.new_source_file(file.into(), html);
let doc = parse_file_as_document(&fm, config, &mut errors)?;
Defensive patterns

Strategy: validation

Validate before calling

fn is_empty_document(html: &str) -> bool {
    let mut rest = html.trim_start();
    while let Some(t) = rest.strip_prefix("<!--") {
        match t.find("-->") {
            Some(i) => rest = t[i + 3..].trim_start(),
            None => return true,
        }
    }
    rest.is_empty()
}

Try / catch

use swc_html_parser::error::ErrorKind;

let mut errors = Vec::new();
let doc = swc_html_parser::parse_file_as_document(&fm, config, &mut errors)?;

for err in &errors {
    if matches!(err.kind(), ErrorKind::EofWithoutDoctype) {
        log::warn!("empty/whitespace-only input parsed as document");
    }
}

Prevention

When it happens

Trigger: parse_document on an empty string, a file containing only whitespace, or only comments (e.g. `<!-- generated -->` with nothing after it).

Common situations: Empty files from failed upstream fetches, placeholder/template files not yet filled, zero-length responses parsed as HTML, comment-only server-side files whose output is empty.

Related errors

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/48608eabb865f750. Report an issue: GitHub.