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• I have searched for related issues and found none that match my proposal.
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Relevant Package

typescript-eslint

My proposal is suitable for this project

• I believe my proposal would be useful to the broader TypeScript community (meaning it is not a niche proposal).

Description

As of #10094, an undefined extension, i.e., undefined as part of extends, will lead to a runtime error of the form

Cannot read properties of undefined (reading "name")

The above PR is the first time that we require that extensions passed to the extends array are actually valid. Note that the config is typed correctly, but that the typechecker cannot help in many cases because the default export, or at least the configs object, of many a plugin is any. Before this PR, undefined extensions were simply ignored silently.

I propose that we improve the error handling of the extends array and instead say something along the following lines whenever we detect an undefined extension:

Some of your extensions are undefined, likely due to a problem with their import path.

Additional Info

Upon upgrading typescript-eslint to 8.10.0, I discovered several undefined extensions but it took me a while to figure out what the problem was because of the initial, not-so-helpful error message. Here is the PR where I upgrade and fix the undefined extension issue in my repo: https://github.com/opossum-tool/OpossumUI/pull/2668/files#diff-9601a8f6c734c2001be34a2361f76946d19a39a709b5e8c624a2a5a0aade05f2L59