Bug: [no-unused-vars] false positive if name is type/value merged and exported

[bradzacher]

Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have searched for related issues and found none that matched my issue.
• I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=4.9.3&jsx=true&sourceType=module&showAST=es&code=C4TwDgpgBAZg9nKBeKBvAvgbgFAQB5hwBOwUAxnAHYDOp8iKAFAIZEDmAXLAgJTIB8abFChEIwAK5FKUVmxzpsQA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Jge1tidmUQAmtAG4BDaKgyRE0aB2iRwYAL4hlQA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA

Repro Code

type foo = {};
export const foo = (arg: foo) => {
  return arg;
}

ESLint Config

module.exports = {
  "rules": {
    "@typescript-eslint/no-unused-vars": "error"
  }
}

tsconfig

{
  "compilerOptions": {
    "strictNullChecks": true
  }
}

Expected Result

no error because the type foo is used and the value foo is exported

Actual Result

'foo' is assigned a value but never used. 2:14 - 2:17

Additional Info

No response

[mithodin]

Also affected by this, we use the following quite often for React components:

interface Test {
    test: string;
}

export const Test = ({ test }: Test) => <>{test}</>;

[Maxim-Mazurok]

Having the same issue with ToStringAble even though it's definitely used:

interface ToStringAble {
  toString(): string;
}
export interface EqualAble {
  equals(other: EqualAble): boolean;
}
export const ToStringAble = (object: ToStringAble): EqualAble => ({
  equals: (other: ToStringAble) => object.toString() === other.toString(),
});

[bradzacher]

The bug is in this function here:

typescript-eslint/packages/eslint-plugin/src/util/collectUnusedVariables.ts

Lines 425 to 440 in 8ee0cbb

	function isExported(variable: TSESLint.Scope.Variable): boolean {
	const definition = variable.defs[0];
	if (definition) {
	let node = definition.node;
	if (node.type === AST_NODE_TYPES.VariableDeclarator) {
	node = node.parent!;
	} else if (definition.type === TSESLint.Scope.DefinitionType.Parameter) {
	return false;
	}
	return node.parent!.type.indexOf('Export') === 0;
	}
	return false;
	}

Specifically that it only considers if the FIRST declaration is exported.
So if the second declaration is exported, the logic doesn't pick that up.
Ideally it should check all declarations to see if any are exported

[Maxim-Mazurok]

Thanks for suggestion @bradzacher , opened PR: #6873