Faster Dev Server Boot

[mcrascal]

npm run dev takes a lot longer to get to a live app than a bare sveltekit app does. In addition to #922, improving this would do a lot for the initial experience of trying out evidence, and for my own day to day experience of using it.

[csjh]

Some profiling suggests a major cause is large files in dependencies taking up a lot of time in a vite function called ssrTransformScript (~4.1s). Main perpetrators:

There's a few other fat time sinks like svelte file compilation (~1.7s) - 170 files are compiled when the dev server is started, so we should figure out if there's a way to avoid that.

[archiewood]

Can't actually see these images, Non-Image content-type returned but I assume they are inadvertent additions?

[csjh]

Whoops, updated

[hughess]

I'm looking through vite config for something else and stumbled upon this warmup option - sharing in case it's useful here: https://vitejs.dev/config/server-options.html#server-warmup

[csjh]

Yeah seems like that helps move the heavy bits to the start of the dev server instead of later in, but the end result is the same

[archiewood]

@csjh what was your rough profiling setup to get these measurements?

[csjh]

@archiewood I've been modifying node_modules/vite/bin/vite.js because their --profile flag wasn't working 100% correctly for me

Basically just go in that file and replace

  session.post('Profiler.enable', () => {
    session.post('Profiler.start', start)
  })

(located near the bottom) with

  session.post('Profiler.enable', () => {
    session.post('Profiler.start', start)
    setTimeout(() => {
        session.post('Profiler.stop', async (err, { profile }) => {
            if (err) {
                console.error(err)
                process.exit(1)
            }
            const fs = await import('node:fs')
            const path = await import('node:path')
            const filename = path.resolve(process.cwd(), 'v8-profile.cpuprofile')
            fs.writeFileSync(filename, JSON.stringify(profile))
            console.log(`Profile written to ${filename}`)
            process.exit(0)
        })
    }, 20000);
  })

and run vite with the --profile flag after the .cpuprofile can be loaded into chrome