"nested" es module imports failing

[harrygr]

Having just upgraded my Remix project to v2 I have set serverModuleFormat to "esm" so I use ES modules.

I have an import somewhere like:

import isValid from "date-fns/isValid";

When I build and run my project I get errors like this:

Error: Directory import '/path/to/project/node_modules/date-fns/isValid' is not supported resolving ES modules imported from /path/to/project/build/index.js
Did you mean to import date-fns/isValid/index.js?

I thought this might be a problem with date-fns, but it looks like date-fns should support ES Module just fine and has a package.json at node_modules/date-fns/isValid that looks like this:

{
  "sideEffects": false,
  "module": "../esm/isValid/index.js",
  "typings": "../typings.d.ts"
}

If I import isValid from the parent module like so it works OK

import { isValid } from "date-fns";

Any ideas why this is?

[pointhalo]

Encountered the same problem when I relied on the locale functionality of date-fns v2.29.3

import { zhCN } from 'date-fns/locale';

❌ in Remix v2
✅ in Remix v1

Hope to get some feasible suggestions