Thanks for the PR, @anikethsaha!

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could you please gate this functionality behind an option, as per my comment: #647 (comment)

I want end-users to opt-in to this functionality so that they're consciously making the decision for a little unsafety from the rule.

ok cool, also it should only check for async iife right ? not just iife ?

it should check both - it should just be looking for an IIFE that returns a promise.

it should check both - it should just be looking for an IIFE that returns a promise.

make sense , ok creating an options name ignoreIife

@bradzacher I think we need to change the selector for AST as well, cause

currently in ExpressionStatement

I have this check

if (options.ignoreIife && isAsyncIife(node)) {
  return;
}

And, here is the definition of isAsyncIife

    function isAsyncIife(node: TSESTree.ExpressionStatement): Boolean {
      if(node?.expression.type === AST_NODE_TYPES.AwaitExpression){
        return true
      }
      if (node?.expression.type === AST_NODE_TYPES.CallExpression) {
        if (possibleIifeCalleType.has(node?.expression?.callee.type)) {
          if (node?.expression?.callee?.hasAsync) {
            return true ;
          }
          return node?.expression?.callee?.body?.body.some(hasPromise);
        }
      }

      return false;
    }

And here is hasPromise

    function hasPromise( node: TSESTree.ExpressionStatement | TSESTree.ReturnStatement): Boolean {
      // has promise statement
      if (node?.expression.type === "NewExpression" && node?.expression?.callee.name === "Promise") {
        return true;
      }
      if (
        // returning promise
        node.type === AST_NODE_TYPES.ReturnStatement &&
        node?.argument.type === AST_NODE_TYPES.NewExpression &&
        node?.argument?.callee.name === "Promise"
      ) {
        return true;
      }
      return false
    }

It looks like when I give input like this

//  options : [{ ignoreIife : true }]
(async function() {
  // error cause of this
  await res(1);
})();

still the there is a floating error.

I did try changing the selectors

["ExpressionStatement > :not(ExpressionStatement )"](node){
  check(node)
},
"ExpressionStatement > ExpressionStatement "(node){
      if(node?.expression.type === AST_NODE_TYPES.AwaitExpression){
        return true
      }
      check(node)
}

Still no luck

the code you've got currently in the PR doesn't look too far off.

I'd expect something along the lines of:

ExpressionStatement(node): void {
  if (options.ignoreIIFE && isIIFE(node)) {
    return;
  }

  // old code
}

function isIIFE(node: TSESTree.ExpressionStatement): boolean {
  const expr = node.expression;
  if (expr.type !== AST_NODE_TYPES.CallExpression) {
    return false;
  }

  return (
    expr.callee.type === AST_NODE_TYPES.ArrowFunctionExpression ||
    expr.callee.type === AST_NODE_TYPES.FunctionExpression
  );
}

To clarify what this option should do:

These cases should error with ignoreIIFE: false (the default)
They should not error with ignoreIIFE: true

(function foo() { return Promise.resolve() })();
(async function foo() { return Promise.resolve() })();
(async () => { return Promise.resolve() })();

However, setting the option to true should not ignore the contents of an IIFE. I.e. this should still error with ignoreIIFE: true

(async () => {
  Promise.resolve(); // error - floating promise
})();
// no other lint error

@bradzacher should I add custom type for isAsyncIife method as I added TSESTree.ExpressionStatement | TSESTree.ArrowFunctionExpression | TSESTree.TSTypeAnnotation type to node but still typecheck is failing.
also, i tried node?.expression.typeAnnotation.typeand still it failed

Codecov Report

Merging #1799 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1799   +/-   ##
=======================================
  Coverage   94.37%   94.37%           
=======================================
  Files         164      164           
  Lines        7572     7579    +7     
  Branches     2175     2178    +3     
=======================================
+ Hits         7146     7153    +7     
  Misses        183      183           
  Partials      243      243           

make sure you run prettier over your code

https://github.com/typescript-eslint/typescript-eslint/blob/master/CONTRIBUTING.md#validating-your-changes

same issue here as well