SKILL: Graceful Export on Application Exit

Pattern: Automatic data export after user-triggered shutdown, with error handling that never blocks exit

Confidence: medium
Source: earned
Tags: #file-io #error-handling #user-experience #cleanup

Problem

Applications with valuable runtime state need to persist data on exit, but export failures shouldn't prevent graceful shutdown or leave the terminal in a broken state.

Solution

Place export logic after the main event loop terminates but before terminal cleanup. Wrap exports in error handling that logs to stderr but allows shutdown to proceed.

Implementation Pattern

rust

fn main() -> io::Result<()> {
    setup_terminal()?;
    
    let result = run();  // Event loop runs here
    
    // Export after event loop, before cleanup
    match exporter.export(&data) {
        Ok(filepath) => {
            eprintln!("Data exported to: {}", filepath.display());
        }
        Err(e) => {
            eprintln!("Warning: Failed to export: {}", e);
        }
    }
    
    cleanup_terminal()?;  // Terminal cleanup always happens
    
    result
}

Key Principles

•
Export after loop exit: User has already signaled intent to quit. Export is "bonus" not blocker.
•
Never panic on export failure: Wrap in match or if let, log errors to stderr, continue to cleanup.
•
Confirm success to user: Print export filepath to stderr so users know where to find saved data.
•
Create directories automatically: Use fs::create_dir_all() so export doesn't fail on missing directories.
•
Order matters: Export → Cleanup → Return. Terminal must be restored even if export fails.

Why Not Alternatives

•❌ Export during event loop: Adds latency to shutdown
•❌ Export before loop starts: No runtime data to save yet
•❌ Panic on export failure: Breaks terminal, terrible UX
•❌ Silent failure: User doesn't know if export worked

Testing

rust

#[test]
fn test_export_failure_doesnt_crash() {
    // Simulate export failure (bad directory, permissions, etc)
    let exporter = MapExporter::new(seed);
    
    // Should return Err, not panic
    let result = exporter.export(&dungeon);
    assert!(result.is_err());
    
    // Application continues and cleans up normally
}

Examples

•Dungeon Saver: Exports ASCII map with metadata on quit
•Game save systems: Write save file before closing window
•Log viewers: Export filtered logs when user quits
•Data analysis tools: Save current workspace/filters on exit

Related Patterns

•See terminal-panic-cleanup for panic hook setup
•See deterministic-game-logic for seed-based generation worth exporting