Update actions/upload-pages-artifact to v4

// This program demonstrates the effect of the v4.0.0 change to
// actions/upload-pages-artifact: dotfiles are not included in the
// artifact by default.  Since we cannot run the GitHub action here,
// we simulate the behavior by creating a temporary directory with
// a normal file and a dotfile, then listing the files that would
// be uploaded.

use std::fs::{self, File};
use std::io::Write;
use std::path::Path;

fn main() -> std::io::Result<()> {
    // Create a temporary directory
    let dir = std::env::temp_dir().join("artifact_demo");
    if dir.exists() {
        fs::remove_dir_all(&dir)?;
    }
    fs::create_dir(&dir)?;

    // Normal file
    let normal_path = dir.join("index.html");
    File::create(&normal_path)?.write_all(b"<html></html>")?;

    // Dotfile
    let dot_path = dir.join(".gitignore");
    File::create(&dot_path)?.write_all(b"*")?;

    // Simulate the artifact upload: list non-dot files
    println!("Files that would be uploaded by v4.0.0:");
    for entry in fs::read_dir(&dir)? {
        let entry = entry?;
        let file_name = entry.file_name();
        let name_str = file_name.to_string_lossy();
        if !name_str.starts_with('.') {
            println!("  {}", name_str);
        }
    }

    // Clean up
    fs::remove_dir_all(&dir)?;
    Ok(())
}