We first tried to introduce this via #13349 for the v9 release. The idea was to define the exports in a non-breaking way, such that all modules under ./lighthouse-core/* / ./lighthouse-cli/* / ./types/* would be exposed + a new export for the renderer api at ./renderer. However, we quickly found that clients (specifically pubads, but if you search GitHb there are tons) tend to import modules with and without a .js extension.

Defining exports like this seemed like it would support optional extension in the import. The first entry that matches the key is used, and the * matches as much as the pattern as possible (includes slashes).

"./lighthouse-core/*.js": "./lighthouse-core/*.js",
"./lighthouse-core/*": "./lighthouse-core/*.js",

However, yarn build-devtools (exercising the pubads code) still failed to resolve all its imports. As this seemed like a huge blocker to adoption for this feature, I began to write a bug report, but first I found these issues in the nodejs project:

nodejs/node#39635

Turns out, "pattern trailers" was an overlooked feature. It was recently added AND backported to 14.

nodejs/Release#690 (comment)

It should land in the next releases across 14+, but IDK when that is. (Ex: 14.18.2 will have the fix, but the latest is 14.18.1. ditto for 17.1.1 see #13359 (comment)). But, it won't be in time for v9.

I can't test it yet, but I believe this will work:

"exports": {
  ".": "./lighthouse-core/index.js",
  "./renderer": "./dist/report/bundle.esm.js",
  "./lighthouse-core/*": "./lighthouse-core/*.js",
  "./lighthouse-core/*.js": "./lighthouse-core/*.js",
  "./lighthouse-cli/*": "./lighthouse-cli/*.js",
  "./lighthouse-cli/*.js": "./lighthouse-cli/*.js",
  "./types/*": "./types/*"
},

(note the order is swapped from the original intuition. not sure why, I'm just copying from the example in the PR)