node resolution not handling flat export maps for files and transient dependency imports

[thescientist13]

Type of Change

• New Feature Request
• Documentation / Website
• Improvement / Suggestion
• Bug
• Other (please clarify below)

Summary

Doing some discovery as part of #523 to validate Greenwood works correctly with a variety of frameworks and libraries, have a couple more improvements to update here regarding integration work in progress with Lion -ProjectEvergreen/greenwood-getting-started#45.

Details

"Flat" Export Map

Was getting an error that one Lion's export maps entries (./define) was not resolving correctly

es-module-shims.js:469 Uncaught (in promise) Error: Unable to resolve specifier '@lion/button/define' from http://localhost:1984/?0
    at throwUnresolved (es-module-shims.js:469)
    at resolve (es-module-shims.js:465)
    at es-module-shims.js:424
    at Array.map (<anonymous>)
    at es-module-shims.js:423
    at async loadAll (es-module-shims.js:237)
    at async topLevelLoad (es-module-shims.js:256)

I think the issue is I was not correctly handling "flat" export maps, e.g.

Lit - each entry is an object

"exports": {
  ".": {
    "default": "./index.js"
  },
  "./async-directive.js": {
    "default": "./async-directive.js"
  },
  "./decorators.js": {
    "default": "./decorators.js"
  },
  "./decorators/custom-element.js": {
    "default": "./decorators/custom-element.js"
  },

  ...
}

Lion - each entry is a string

"exports": {
  ".": "./index.js",
  "./define": "./lion-calendar.js",
  "./translations/*": "./translations/*",
  "./test-helpers": "./test-helpers/index.js",
  "./docs/": "./docs/"
}  

Transient Imports

After fixing the above, I then saw that an import of a dependent package was not correctly getting updated in the import map when walking a module.

es-module-shims.js:469 Uncaught (in promise) Error: Unable to resolve specifier '@bundled-es-modules/message-format/MessageFormat.js' from http://localhost:1984/node_modules/@lion/localize/src/LocalizeManager.js
    at throwUnresolved (es-module-shims.js:469)
    at resolve (es-module-shims.js:465)
    at es-module-shims.js:424
    at Array.map (<anonymous>)
    at es-module-shims.js:423

Not sure if this is just bad export map reading on my end, but presumably all import statements needs to be registered in the import map somewhere, right?

---

There might be some other fixes needed as part of working with MWC and the double scoped namespace bug seen, but will save that for another issue / PR.