ESM config w/ .mjs not loadable?

[maxfierke]

According to the v4 migration guide, because the app I'm working on directly imports rules, I need to convert it to ESM. However, when I do so, it doesn't seem like it can find the config? (.template-lintrc.mjs)

Does this only work if "type": "module" is specified in package.json? I don't seem to be able to turn that on without infecting everything and running into other packages (or ember-cli) that cannot find a corresponding .cjs file when their configuration is still CommonJS.

$ yarn lint
yarn run v1.22.18
$ npm-run-all --aggregate-output --continue-on-error --parallel "lint:!(fix)"
(node:74494) UnhandledPromiseRejectionWarning: Error: The configuration file specified (.template-lintrc.js) could not be found. Aborting.
    at resolveProjectConfig (file:///Users/mfierke/src/MY_APP/node_modules/ember-template-lint/lib/get-config.js:68:13)
    at getProjectConfig (file:///Users/mfierke/src/MY_APP/node_modules/ember-template-lint/lib/get-config.js:407:41)
    at Linter.loadConfig (file:///Users/mfierke/src/MY_APP/node_modules/ember-template-lint/lib/linter.js:45:25)
    at Linter.verify (file:///Users/mfierke/src/MY_APP/node_modules/ember-template-lint/lib/linter.js:301:18)
    at run (file:///Users/mfierke/src/MY_APP/node_modules/ember-template-lint/bin/ember-template-lint.js:215:34)
(node:74494) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:74494) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

What are my options here? I seem to need 4.x to fix parsing issues when trying to address the argument-less-helper-paren-less-invocation deprecation in Ember 3.27+ (ref #2163), otherwise I would just avoid upgrading until a point where I could ESM-ify everything.

To be clear, I'm able to workaround my underlying issue on 3.x by using Yarn resolutions for ember-template-lint/ember-template-recast but that feels icky.

[lifeart]

@maxfierke #2339 may fix it, could you create minimal test case for it?

[maxfierke]

Closing this out. I ended up abandoning whatever effort I was doing here and someone was able to get it working fine on v5 last week, so 🤷