feat: introduce RunnableDevEnvironment

[sheremet-va]

Description

This PR introduces a new concept to the Environment API - the RunnableDevEnvironment. This is the environment that has a module runner in the same process. You can access it directly as environment.runner. The runner itself is evaluated eagerly when it's accessed for the first time.

By default, Vite SSR dev environment is a runnable environment. Due to environments being available during the build, there are some constraints in typing. You can either cast it to RunnableDevEnvironment or type guard it with isRunnableDevEnvironment.

import { createServer, isRunnableDevEnvironment } from 'vite'
import type { RunnableDevEnvironment } from 'vite'

const server = createServer()
const ssrEnvironment = server.environments.ssr as RunnableDevEnvironment

if (isRunnableDevEnvironment(ssrEnvironment)) {
  await ssrEnvironment.runner.import('/entry-point.js')
}

You can create your own runnable environments using the createRunnableDevEnvironment function:

import { createRunnableDevEnvironment } from 'vite'

const environment = createRunnableDevEnvironment(name, config)
await environment.runner.import('/entry-point.js')

You can configure the runner with the runner option (the previous runner option was renamed to remoteRunner):

import { createRunnableDevEnvironment, createServerModuleRunner } from 'vite'

const environment = createRunnableDevEnvironment(name, config, {
  runner: (env) => createServerModuleRunner(env, { hmr: false })
})
await environment.runner.import('/entry-point.js')

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[patak-dev]

Nice! I think this should help a lot with the ssrLoadModule migration story. I think we should merge it to keep exploring. If others think we should review this, we can later revert it before the release.

[silvenon]

I like that this is already a part of SSR by default ❤️

Can you clarify what this means?

The runner itself is evaluated eagerly when it's accessed for the first time.

[sheremet-va]

I like that this is already a part of SSR by default ❤️

Can you clarify what this means?

The runner itself is evaluated eagerly when it's accessed for the first time.

Basically, the runner doesn't exist until it's called. I don't know how else to explain it. It's evaluated lazily.

It's important to know because the initialisation of the runner has side effects. More is explained in the docs.