biomejs/biome · error

found a token with no parent

Error message

found a token with no parent

What it means

Panic in the CSS format-on-type handler (css.rs:662). After locating the token under the cursor via token_at_offset, the code calls token.parent(); in a rowan syntax tree the root is always a node, so a token retrieved from token_at_offset normally always has a parent. This branch is a defensive assertion that fires only if the token is detached or the tree root were a bare token - states that should not occur for tokens produced by the parser.

Source

Thrown at crates/biome_service/src/file_handlers/css.rs:662

        // 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: CssSyntaxNode| node.kind().is_bogus())
    {
        return Ok(format_on_type_noop(offset));
    }

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

fn lint(params: LintParams) -> LintResults {
    let Some(file_source) = params.language.to_css_file_source() else {
        return LintResults {
            diagnostics: vec![],

View on GitHub (pinned to 405dedb0ff)

Solutions

1. Update to the latest Biome patch release in case the branch was removed or the underlying parse issue fixed
2. Capture a minimal document plus keystroke that reproduces it and file an issue at https://github.com/biomejs/biome/issues
3. If you embed biome_service, run the workspace inside catch_unwind so an on-type panic degrades to 'no formatting' instead of taking down the host

// LSP client - degrade gracefully if the server dies on an on-type request
try {
  const edits = await client.sendRequest('textDocument/onTypeFormatted', params);
} catch {
  // formatting failed server-side; leave the buffer untouched instead of surfacing an error
}

When it happens

Trigger: Effectively unreachable through normal LSP traffic: any token returned by tree.token_at_offset(offset) belongs to the tree and has a parent node. Would only fire through API misuse (passing a detached token) or an exotic parse producing a token-rooted tree.

Common situations: Almost never seen in practice; appears in crash reports only alongside corrupted or hand-constructed syntax trees, or after internal refactors of the parser.

Related errors

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

AI-assisted analysis of biomejs/biome@405dedb0ff (2026-08-20). Data as JSON: /api/errors/fd26fe59124d3566. Report an issue: GitHub.