biomejs/biome · error

found a token with no parent

Error message

found a token with no parent

What it means

Panic in the JSON format-on-type handler (json.rs:612). After locating the token at the cursor, the handler calls token.parent(); tokens returned by token_at_offset on a parsed rowan tree always have a parent node since the root is a node. This is a defensive assertion for detached or token-rooted trees, which the normal parse path cannot produce.

Source

Thrown at crates/biome_service/src/file_handlers/json.rs:612

        // File is empty, do nothing
        TokenAtOffset::None => panic!("empty file"),
        TokenAtOffset::Single(token) => token,
        // The cursor should be right after the closing character that was just typed,
        // select the previous token as the correct one
        TokenAtOffset::Between(token, _) => token,
    };

    if token.text_trimmed_range().end() != offset {
        return Ok(format_on_type_noop(offset));
    }

    if !matches_on_type_char(token.text_trimmed()) {
        return Ok(format_on_type_noop(offset));
    }

    let root_node = match token.parent() {
        Some(node) => node,
        None => panic!("found a token with no parent"),
    };

    if root_node
        .ancestors()
        .any(|node: JsonSyntaxNode| node.kind().is_bogus())
    {
        return Ok(format_on_type_noop(offset));
    }

    let printed =
        biome_json_formatter::format_range(options, &tree, root_node.text_trimmed_range())?;
    Ok(printed)
}

fn lint(params: LintParams) -> LintResults {
    let _ = debug_span!("Linting JSON file", path =? params.path, language =? params.language)
        .entered();
    let Some(file_source) = params

View on GitHub (pinned to 405dedb0ff)

Solutions

1. Update to the latest Biome release
2. Report a reproducer to https://github.com/biomejs/biome/issues if you can trigger it
3. Embedders: guard the call with catch_unwind and degrade to no formatting

// LSP client - on-type formatting is best-effort
try {
  const edits = await client.sendRequest('textDocument/onTypeFormatted', params);
} catch {
  // ignore server-side failure; buffer stays as typed
}

When it happens

Trigger: Not reachable through normal LSP requests; only a detached token or a token as tree root would trigger it.

Common situations: Effectively theoretical; only plausible with hand-constructed syntax trees or internal API misuse.

Related errors

• found a token with no parent
• found a token with no parent
• found a token with no parent
• empty file
• found a token with no parent

AI-assisted analysis of biomejs/biome@405dedb0ff (2026-08-20). Data as JSON: /api/errors/dcb1fc3e29e96ef5. Report an issue: GitHub.