Enhancement: [no-unnecessary-condition] Check truthiness assertion functions

[kirkwaiblinger]

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• I have searched for related issues and found none that match my proposal.
• I have searched the current rule list and found no rules that match my proposal.
• I have read the FAQ and my problem is not listed.

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Link to the rule's documentation

https://typescript-eslint.io/rules/no-unnecessary-condition/

Description

This is spinoff from the corresponding issue for strict-boolean-expressions.

Following the conversation from #9009 (comment), it is proposed that strict-boolean-expressions also check the asserting argument of an assertion function as a boolean context for an unnecessary condition.

However, for this rule, that behavior should definitely be behind an option, since assertion functions can often be used to assert that something which appears to be true according to the types actually is true at runtime. Codebases that do so regularly will probably want to disable this behavior.

Fail

function assert(x: unknown): asserts x {
  if (!x) {
    throw new Error('assertion');
  }
}

const truthyString = 'string';
assert(truthyString)

Pass

function assert(x: unknown): asserts x {
  if (!x) {
    throw new Error('assertion');
  }
}

assert(Math.random() > 0.5)

Additional Info

No response