A dependency having an export map without a "." field will cause SSR imports to throw

[ggoodman]

Describe the bug

Given an npm module that has an export map defining deep imports but NOT defining a root import such as the one for nostalgie, the heuristics for determining if the module should be treated as 'external' or not will throw due to the call here:

vite/packages/vite/src/node/ssr/ssrExternal.ts

Line 32 in b2110af

const entry = tryNodeResolve(id, undefined, root, false)?.id

.

The resulting stack trace will be something like:

Error: Missing "." export in "nostalgie" package
    at bail (/Users/ggoodman/Projects/ggoodman/nostalgie/node_modules/vite/dist/node/chunks/dep-0b3f4801.js:40013:8)
    at resolve$1 (/Users/ggoodman/Projects/ggoodman/nostalgie/node_modules/vite/dist/node/chunks/dep-0b3f4801.js:40089:10)
    at resolveExports (/Users/ggoodman/Projects/ggoodman/nostalgie/node_modules/vite/dist/node/chunks/dep-0b3f4801.js:40099:12)
    at resolvePackageEntry (/Users/ggoodman/Projects/ggoodman/nostalgie/node_modules/vite/dist/node/chunks/dep-0b3f4801.js:40389:22)
    at tryNodeResolve (/Users/ggoodman/Projects/ggoodman/nostalgie/node_modules/vite/dist/node/chunks/dep-0b3f4801.js:40289:11)
    at resolveSSRExternal (/Users/ggoodman/Projects/ggoodman/nostalgie/node_modules/vite/dist/node/chunks/dep-0b3f4801.js:40553:29)

Reproduction

This can be reproduced with the following:

npm install --save nostalgie

src/App.tsx:

import { useAuth } from 'nostalgie/auth';

export default function App() {
  const appState = useAuth();
}

bundler.ts:

import pluginReactRefresh from '@vitejs/plugin-react-refresh';
import * as Path from 'path';
import { createLogger, createServer, Logger, ViteDevServer } from 'vite';
import type { RuntimeConfiguration } from './types';

const logger = createLogger();

async function main(logger: Logger, config: RuntimeConfiguration) {
  const vite = await createServer({
    plugins: [pluginReactRefresh()],
  });

  const foo = await importReactApp(logger, config, vite);

  console.dir(foo);
}

function importReactApp(logger: Logger, config: RuntimeConfiguration, vite: ViteDevServer) {
  return (vite as any).ssrLoadModule(config.reactAppEntryPath) as Promise<() => JSX.Element>;
}

const rootDir = Path.resolve(__dirname, '.'); // Modified for this repro

main(logger, {
  nodeEnv: 'development',
  reactAppEntryPath: Path.resolve(rootDir, './src/App.tsx'),
  rootPath: rootDir,
}).catch((err) => {
  logger.error(err);
  process.exit(1);
});

System Info

• vite version: 2.0.0-beta.62
• Operating System: MacOS 11.2
• Node version: v14.15.4
• Package manager (npm/yarn/pnpm) and version: 6.14.10

Logs (Optional if provided reproduction)

1. Run vite or vite build with the --debug flag. N/A
2. Provide the error log here. See above