fix: apply Vite resolving algorithm to node_modules libraries

examples/solid/vite.config.mjs

@@ -10,9 +10,6 @@ export default defineConfig({
     transformMode: {
       web: [/.[jt]sx?/],
     },
-    deps: {
-      inline: [/solid-js/],
-    },
     threads: false,
     isolate: false,
   },

packages/vitest/package.json

@@ -62,7 +62,7 @@
   },
   "scripts": {
     "build": "rimraf dist && rollup -c",
-    "dev": "rollup -c --watch -m inline",
+    "dev": "NODE_OPTIONS=\"--max-old-space-size=8192\" rollup -c --watch -m inline",
     "prepublishOnly": "nr build"
   },
   "peerDependencies": {

packages/vitest/rollup.config.js

@@ -20,6 +20,7 @@ const entries = [
   'src/node/cli.ts',
   'src/node.ts',
   'src/runtime/worker.ts',
+  'src/runtime/loader.ts',
   'src/runtime/entry.ts',
   'src/runtime/suite.ts',
   'src/integrations/spy.ts',

packages/vitest/src/constants.ts

@@ -1,6 +1,7 @@
 import url from 'url'
 import { resolve } from 'pathe'
 
+export const rootDir = resolve(url.fileURLToPath(import.meta.url), '../../')
 export const distDir = resolve(url.fileURLToPath(import.meta.url), '../../dist')
 
 // if changed, update also jsdocs and docs

packages/vitest/src/node/pool.ts

@@ -7,7 +7,7 @@ import { Tinypool } from 'tinypool'
 import { createBirpc } from 'birpc'
 import type { RawSourceMap } from 'vite-node'
 import type { ResolvedConfig, WorkerContext, WorkerRPC } from '../types'
-import { distDir } from '../constants'
+import { distDir, rootDir } from '../constants'
 import { AggregateError } from '../utils'
 import type { Vitest } from './core'
 
@@ -19,6 +19,9 @@ export interface WorkerPool {
 }
 
 const workerPath = _url.pathToFileURL(resolve(distDir, './worker.mjs')).href
+const loaderPath = _url.pathToFileURL(resolve(distDir, './loader.mjs')).href
+
+const suppressLoaderWarningsPath = resolve(rootDir, './suppress-warnings.cjs')
 
 export function createPool(ctx: Vitest): WorkerPool {
   const threadsCount = ctx.config.watch
@@ -28,6 +31,8 @@ export function createPool(ctx: Vitest): WorkerPool {
   const maxThreads = ctx.config.maxThreads ?? threadsCount
   const minThreads = ctx.config.minThreads ?? threadsCount
 
+  const conditions = ctx.server.config.resolve.conditions?.flatMap(c => ['-C', c])
+
   const options: TinypoolOptions = {
     filename: workerPath,
     // TODO: investigate further
@@ -36,6 +41,14 @@ export function createPool(ctx: Vitest): WorkerPool {
 
     maxThreads,
     minThreads,
+
+    execArgv: [
+      '--require',
+      suppressLoaderWarningsPath,
+      '--experimental-loader',
+      loaderPath,
+      ...conditions || [],
+    ],
   }
 
   if (ctx.config.isolate) {

packages/vitest/src/runtime/loader.ts

@@ -0,0 +1,31 @@
+import { pathToFileURL } from 'url'
+import { isNodeBuiltin } from 'mlly'
+import { normalizeModuleId } from 'vite-node/utils'
+import { getWorkerState } from '../utils'
+import type { Loader, Resolver } from '../types/loader'
+
+// apply transformations only to libraries
+// inline code preccessed by vite-node
+export const resolve: Resolver = async (url, context, next) => {
+  const { parentURL } = context
+  if (!parentURL || !parentURL.includes('node_modules') || isNodeBuiltin(url))
+    return next(url, context, next)
+
+  const id = normalizeModuleId(url)
+  const importer = normalizeModuleId(parentURL)
+  const state = getWorkerState()
+  const resolver = state?.rpc.resolveId
+  if (resolver) {
+    const resolved = await resolver(id, importer)
+    if (resolved) {
+      return {
+        url: pathToFileURL(resolved.id).toString(),
+      }
+    }
+  }
+  return next(url, context, next)
+}
+
+export const load: Loader = (url, context, next) => {
+  return next(url, context, next)
+}

packages/vitest/src/types/loader.ts

@@ -0,0 +1,37 @@
+import type { Awaitable } from './general'
+
+interface ModuleContext {
+  conditions: string[]
+  parentURL?: string
+}
+
+enum ModuleFormat {
+  Builtin = 'builtin',
+  Commonjs = 'commonjs',
+  Json = 'json',
+  Module = 'module',
+  Wasm = 'wasm',
+}
+
+interface ResolveResult {
+  url: string
+  format?: ModuleFormat
+}
+
+export interface Resolver {
+  (url: string, context: ModuleContext, next: Resolver): Awaitable<ResolveResult>
+}
+
+interface LoaderContext {
+  format: ModuleFormat
+  importAssertions: Record<string, string>
+}
+
+interface LoaderResult {
+  format: ModuleFormat
+  source: string | ArrayBuffer | SharedArrayBuffer | Uint8Array
+}
+
+export interface Loader {
+  (url: string, context: LoaderContext, next: Loader): Awaitable<LoaderResult>
+}

packages/vitest/suppress-warnings.cjs

@@ -0,0 +1,20 @@
+// borrowed from tsx implementation:
+// https://github.com/esbuild-kit/tsx
+
+const ignoreWarnings = new Set([
+  '--experimental-loader is an experimental feature. This feature could change at any time',
+  'Custom ESM Loaders is an experimental feature. This feature could change at any time',
+])
+
+const { emit } = process
+
+process.emit = function (event, warning) {
+  if (
+    event === 'warning'
+    && ignoreWarnings.has(warning.message)
+  )
+    return
+
+  // eslint-disable-next-line prefer-rest-params
+  return Reflect.apply(emit, this, arguments)
+}