chore: add lint:unused script to run Knip

[JoshuaKGoldberg]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Adds Knip to check for unused exports, unused dependencies, and missing dependencies

What changes did you make? (Give an overview)

1. Adds Knip, similar to how it was done in the eslint/eslint repo in chore: Introduce Knip eslint#18005.
2. Adds in devDependencies that it noted are relied upon but don't exist
3. Adds -y to the jsr launch to explicitly always run it without prompting

Related Issues

Related to #462, which found types exported by the package but not used anywhere.

Is there anything you'd like reviewers to focus on?

[snitin315]

Why is CI green when we have unused exports in the main branch, as per #462?

[lumirlumir]

Hi @snitin315,

I'm not Joshua, but I found this comment in #462 😅

Unfortunately it can't detect this specific issue because types.ts is an entry point per package.json > "exports". From Knip's perspective, anything that is exported from an entry point is "used". Sent: #466.

Currently, since the types.d.ts file is exported via the exports field, I think Knip can't detect it as unused—it considers anything exported from an entry point as "used."

markdown/package.json

Lines 13 to 21 in 094a59d

	"exports": {
	".": {
	"types": "./dist/esm/index.d.ts",
	"default": "./dist/esm/index.js"
	},
	"./types": {
	"types": "./dist/esm/types.d.ts"
	}
	},

[lumirlumir]

Today I learned what Knip does 😄

I'm in favor of this change 👍, but I'll move it to the Feedback Needed section for now to gather more input.

I've also left a minor comment.

[lumirlumir]

I’ll check back in once a decision has been made 😄

[nzakas]

Generally I'm on the side of more tooling, I'd just like a better explanation of what prompted this PR and why the check is green if there are unused exports.

[github-actions]

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[JoshuaKGoldberg]

what prompted this PR

It's the two reasons noted in the OP:

• chore: Introduce Knip eslint#18005: Knip is a generally useful tool that finds unused code. I figured I'd add it in now while the repo is relative younger and doesn't have as much cruft built up.
• fix: remove unused types from types.ts #462: even though that specific classification of unused code can't be caught by Knip, the fact that there are things building up IMO is a signal that something like Knip would be useful

why the check is green if there are unused exports

It's #466 (comment) <- #462 (comment). The specific kind of issue in #462 -a type being exported out of the package but not used by any external consumers- is out of scope for Knip.

[lumirlumir]

Suggested change

	"entry": ["tests/**/*.test.js", "tests/fixtures/*.js"],
	"entry": ["tests/**/*.test.{js,ts}", "tests/fixtures/*.js"],

I have a question. In https://github.com/eslint/rewrite/pull/241/files the ts test files are included — should we include ts here as well? There's a types.test.ts in the tests directory.

https://github.com/eslint/markdown/blob/main/tests/types/types.test.ts