Drop Recommended Rules for Deprecated Ember 3.x Features about ember-template-lint

[elwayman02]

For visibility and cross-referencing decisions on how to move forward consistently, I've filed a similar issue for eslint-plugin-ember: ember-cli/eslint-plugin-ember#1950

[bmish]

Thanks for the proposal.

I generally do not agree with removing rules from the recommended config just because they are targeting old Ember versions.

I'd prefer that we keep rules in the recommended config unless they are incompatible with modern Ember and it's not possible to make them compatible. Oftentimes, we can update a rule with a simple fix or heuristic in order to ensure cross-version compatibility. But in my experience, incompatibilities are rare, and most rules targeting old Ember versions do not cause any issues.

In addition, needlessly removing rules from the config causes churn when there's little or no cost to continuing to include them. Something that does have a cost (in terms of maintenance burden and reduced ease-of-use) is adding additional configs.

And while we don't technically need to support users on Ember 3 anymore, I'm happy to continue supporting them if the cost is minimal. Especially when most of these older rules are simply about detecting deprecated patterns that aren't supported anymore but could easily pop-up when copy-pasting in code from an old article or codebase or receiving a suggestion from an AI copilot, etc.

So what I would recommend is:

1. Identify the complete list of recommended rules that are incompatible with modern Ember. I only see no-implicit-this mentioned regarding this.
2. Determine if incompatible rules can be made compatible (e.g. become a no-op if they aren't relevant anymore).
3. If there are truly incompatible rules that cannot be updated to co-exist across Ember versions, remove these from the recommended config as a breaking change in a major release.

[bertdeblock]

FYI, the unbound helper was never deprecated nor removed, so I think the no-unbound rule is still relevant.

[elwayman02]

FYI, the unbound helper was never deprecated nor removed, so I think the no-unbound rule is still relevant.

Good catch. I saw it was marked deprecated in Ember 1.x, but I guess they never got around to removing it...