emilk/egui · error

Failed to create temp file

Error message

Failed to create temp file

What it means

Error "Failed to create temp file" thrown in emilk/egui.

Source

Thrown at crates/egui_kittest/src/snapshot.rs:809

    }

    /// Render a snapshot, save it to a temp file and open it in the default image viewer.
    ///
    /// This method is marked as deprecated to trigger errors in CI (so that it's not accidentally
    /// committed).
    #[deprecated = "Only for debugging, don't commit this."]
    #[cfg(not(target_arch = "wasm32"))]
    pub fn debug_open_snapshot(&mut self) {
        let image = self
            .render()
            .map_err(|err| SnapshotError::RenderError { err })
            .unwrap();
        let temp_file = tempfile::Builder::new()
            .disable_cleanup(true) // we keep the file so it's accessible even after the test ends
            .prefix("kittest-snapshot")
            .suffix(".png")
            .tempfile()
            .expect("Failed to create temp file");

        let path = temp_file.path();

        image
            .save(temp_file.path())
            .map_err(|err| SnapshotError::WriteSnapshot {
                err,
                path: path.to_path_buf(),
            })
            .unwrap();

        // Close temp file so it isn't locked when `open` tries to launch it (on Windows)
        let path = temp_file.into_temp_path();

        #[expect(clippy::print_stdout)]
        {
            println!("Wrote debug snapshot to: {}", path.display());
        }

View on GitHub (pinned to b9a0723d88)

Solutions

1. The temp directory is missing or not writable: set TMPDIR (or platform temp dir) to a writable location before running snapshot tests.
2. Ensure there is free disk space for the temporary screenshot file.

Example fix

std::env::set_var("TMPDIR", "/writable/tmp"); // before running snapshot tests

When it happens

Trigger: Thrown at crates/egui_kittest/src/snapshot.rs:809 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of emilk/egui@b9a0723d88 (2026-08-19). Data as JSON: /api/errors/a915be16d98afd6e. Report an issue: GitHub.