util: attach return value to promisified functions

[Hakerh400]

Some functions that perform asynchronous tasks and
take a callback also return a synchronous result which
can be used in the same tick. Previously util.promisify
was discarding the return value.

While #28325 solved the problem for some specific functions, the general problem for user-defined functions remained. It seems that not so rare practice is to return a useful value along with scheduling asynchronous actions in a function which takes a callback.

Documentation is not added yet. I would like to hear some feedback first regarding whether this change is a good change (or maybe some better suggestions for the symbol name?).

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[devsnek]

this seems best left to the specific function. we probably want to avoid weird new patterns in the ecosystem like checking promises for node symbols.

[BridgeAR]

I think a good alternative to adding this is to document how to use a custom promisify function that does exactly this? If we go for something like this, a better name might be: syncValue, syncReturn, returnValue or something like that?

[BridgeAR]

@nodejs/promises-debugging @nodejs/util PTAL

[benjamingr]

This is not really idiomatic and it makes more sense to decorate the promise value and not the function return value.

I'm not in favour of this landing.

It is an interesting idea though - would love to see more :]