Dependency entry point lookup

[Xiot]

How does the resolution for finding the entrypoint for a package work?
I have a package that as main, module as well as browser fields defined in its package.json, but I don't see a way to specify which one to use.

I see installOptions.packageLookupFields but its usage isn't very clear as it looks like it takes an array of package names.

My use case is that I have a package that has both a client and a server build, so I need to select the correct one.
By default it looks like its always selecting the browser package.

Is there a way to specify that the build should target node and not the browser?

[Xiot]

Looking through the code, I figured out how installlOptions.packageLookupFields work.
Using esinstall directly, I can see that its finding the correct entry point, however it looks like rollup is using the wrong one.

import {install} from 'esinstall';
await install(['fusion-core']);

The output from that is

running installer with options: {
  input: {
    'fusion-core': '/Users/tchrs/dev/github/xiot/fusion-react-esbuild/node_modules/fusion-core/dist-node-esm/index.js'
  },
  context: undefined,
  external: [Function: external],
  treeshake: { moduleSideEffects: 'no-external' },
  plugins: [
    { name: 'alias', resolveId: [Function: noop] },
    {
      name: 'snowpack:fetch-handler',
      resolveId: [Function: resolveId],
      load: [Function: load]
    },
    {
      name: 'node-resolve',
      buildStart: [Function: buildStart],
      generateBundle: [Function: generateBundle],
      resolveId: [AsyncFunction: resolveId],
      load: [Function: load],
      getPackageInfoForId: [Function: getPackageInfoForId]
    },
    { name: 'json', transform: [Function: transform] },
    {
      name: 'snowpack:rollup-plugin-css',
      transform: [AsyncFunction: transform]
    },
    {
      name: 'replace',
      renderChunk: [Function: renderChunk],
      transform: [Function: transform]
    },
    {
      name: 'commonjs',
      buildStart: [Function: buildStart],
      resolveId: [Function: resolveId],
      load: [Function: load],
      transform: [Function: transform],
      moduleParsed: [Function: moduleParsed]
    },
    {
      name: 'snowpack:wrap-install-targets',
      buildStart: [Function: buildStart],
      resolveId: [Function: resolveId],
      load: [Function: load]
    },
    {
      name: 'snowpack:rollup-plugin-stats',
      generateBundle: [Function: generateBundle],
      writeBundle: [Function: writeBundle]
    },
    {
      name: 'snowpack:rollup-plugin-node-process-polyfill',
      transform: [Function: transform],
      resolveId: [Function: resolveId],
      load: [Function: load]
    },
    {
      name: 'snowpack:rollup-plugin-catch-unresolved',
      resolveId: [Function: resolveId]
    },
    {
      name: 'snowpack:rollup-plugin-strip-source-mapping',
      transform: [Function: transform]
    }
  ],
  onwarn: [Function: onwarn]
}
cjsAutoDetectExportsUntrusted error: Unexpected import statement in CJS module.
  at @:8:8
node_modules/fusion-core/dist-browser-esm/get-env.js
   Module "assert" (Node.js built-in) is not available in the browser. Run Snowpack with --polyfill-node to fix.
installing npm packages:
    fusion-core
/Users/tchrs/dev/github/xiot/fusion-react-esbuild/node_modules/esinstall/lib/index.js:414
                throw new Error(FAILED_INSTALL_MESSAGE);
                      ^

Error: Install failed.
    at install (/Users/tchrs/dev/github/xiot/fusion-react-esbuild/node_modules/esinstall/lib/index.js:414:23)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at async file:///Users/tchrs/dev/github/xiot/fusion-react-esbuild/install-test.js:3:13

The relevant bits from the fusion-core/package.json are

  "main": "./dist-node-cjs/index.js",
  "module": "./dist-node-esm/index.js",
"browser": {
    "./dist-node-cjs/index.js": "./dist-browser-cjs/index.js",
    "./dist-node-esm/index.js": "./dist-browser-esm/index.js"
  },

So it appears that esinstall is picking the correct entry point, however rollup is swapping it out for the browser version