Minify prerendered HTML (and app.html?)

sapper export minifies the generated HTML. Perhaps we should do the same thing here?

// svelte.config.cjs
module.exports = {
  kit: {
    prerender: {
      minify: true
    }
  }
};

// svelte.config.cjs
module.exports = {
  kit: {
    prerender: {
      minify: {
        // manually specify options (https://www.npmjs.com/package/html-minifier)
        collapseBooleanAttributes: true
        // ...
      }
    }
  }
};

We could potentially do the same thing for src/app.html, though the benefits are less pronounced.

[Conduitry]

Being able to control the minification options (or disabling it entirely) sounds good, as this is one of the requested Sapper features that we deferred on because of a lack of a sane way to handle configuration.

I have mixed feelings about whether this should be enabled by default for prerendered sites. It’s probably a good idea, but then it’s also been the subject of a whole lot of invalid Sapper bugs.

I agree that it’s probably only a good idea to include this on HTML that can be minified during build time and not at runtime.

[Rich-Harris]

I’d like it if it was a bit more turnkey but it does seem very difficult to offer sensible defaults. Without configuration it won’t do a whole lot for you. So it probably doesn’t make sense to weigh the package down with a dependency that won’t do very much for most people.