slint-ui/slint · error · std::io::Error

File not found

Error message

File not found

What it means

In the live-preview session's message processing, when a file's cache entry is in the Loading state and the file turns out to be gone (e.g. a delete event arrived), all pending load senders are resolved with a NotFound 'File not found' io::Error. Anyone awaiting that file's contents receives this error.

Solutions

1. Recreate or restore the deleted file so the loader can resolve it.
2. Handle the NotFound error in the code awaiting the file load and skip/cancel compilation of that file.
3. Trigger a reload of the session's file list so the deleted path is no longer requested.

Example fix

// before
let content = load_file(url).await?; // panics/aborts on NotFound
// after
match load_file(url).await {
    Ok(c) => compile(c),
    Err(e) if e.kind() == std::io::ErrorKind::NotFound => log::warn!("{url} deleted; skipping"),
    Err(e) => return Err(e.into()),
}

// before requesting, confirm the file exists
if !std::path::Path::new(&file_path).exists() { skip_load(); }

match load_file(url).await {
    Ok(c) => compile(c),
    Err(e) if e.kind() == ErrorKind::NotFound => /* file deleted; skip */,
    Err(e) => return Err(e.into()),
}

When it happens

Trigger: A file is deleted (or its URL no longer maps to an existing file) while the preview had registered load waiters under CacheEntry::Loading; process_message handles the removal and broadcasts the error to every waiting sender.

Common situations: Deleting or renaming a .slint file in the editor while preview is loading/compiling it; file watchers firing remove events mid-load; stale editor buffers referencing removed files.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

Related errors

• Preview session is no longer available
• Cannot get property
• Cannot get property
• Cannot invoke callback
• Cannot invoke callback

AI-assisted analysis of slint-ui/slint@bb937076de (2026-09-16). Data as JSON: /api/errors/0a75735e69ab4eb7. Report an issue: GitHub.

Appendix: source

Thrown at internal/live-preview/preview_sessions.rs:178

        debounce_deadline: &mut Option<tokio::time::Instant>,
    ) -> bool {
        match message {
            LspToPreviewMessage::InvalidateContents { url } => {
                if !is_supported(&url) {
                    return true;
                }
                self.file_cache.borrow_mut().remove(&url);
                self.schedule_rebuild(&url, debounce_deadline);
            }
            LspToPreviewMessage::ForgetFile { url } => {
                if !is_supported(&url) {
                    return true;
                }
                if let Some(CacheEntry::Loading(senders)) =
                    self.file_cache.borrow_mut().remove(&url)
                {
                    for sender in senders {
                        let _ = sender.send(Err(std::io::Error::new(
                            std::io::ErrorKind::NotFound,
                            "File not found",
                        )));
                    }
                }
                self.schedule_rebuild(&url, debounce_deadline);
            }
            LspToPreviewMessage::SetContents { url, contents } => {
                if !is_supported(url.url()) {
                    return true;
                }
                if i_slint_compiler::pathutils::is_font_file(url.url().path()) {
                    event_handler(PreviewSessionEvent::RegisterFont {
                        url: url.url().clone(),
                        contents: contents.into(),
                    });
                    return true;
                }

View on GitHub (pinned to bb937076de)