Why post function declaration would not be treeshake?

[LongTengDao]

• Rollup Version: 1.14.4
• Operating System (or Browser):
• Node Version:

How Do We Reproduce?

var successShaked = function () {
    function inner () {
        /* ... */
    }
    return function outer (){
        return /*#__PURE__*/ inner();
    };
}();
successShaked();
var failedShaked = function () {
    return function outer (){
        return /*#__PURE__*/ inner();
    };
    function inner () {
        /* ... */
    }
}();
failedShaked();

Expected Behavior

Both be shaked.

Actual Behavior

Leave this:

var failedShaked = function () {
    return function outer (){
        return /*#__PURE__*/ inner();
    };
    function inner () {
        /* ... */
    }
}();
failedShaked();

[lukastaegert]

The problem is probably that the algorithm to determine side-effects of function return values tries to "cache" the return value at an early stage where the function definition has not been properly processed. Marking this as an "enhancement" as the generated code is not broken but could be optimized better.

[antfu]

I guess static side-effects analysis will always reach limitations for dynamic parts. #5024 introduced the annotation to manually mark functions as side-effects-free, which I think should be able to solve this issue.