Revert "Improve output when wrapping functions"

[jjonescz]

Q	A
Fixed Issues?	Fixes #15978
Patch: Bug Fix?	Yes
Major: Breaking Change?	No
Minor: New Feature?	No
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	No
License	MIT

This adds a new test to reproduce the bug and reverts #15978 (without removing new tests added there). That's the simplest fix I could think of for now.
cc @liuxingbaoyu

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/55482/

[nicolo-ribaudo]

Could we revert just the changes relative to function expressions and not to function declarations?

[jjonescz]

Could we revert just the changes relative to function expressions and not to function declarations?

Do you mean that the optimization would apply to expressions but not declarations? Could that be done in a follow up PR - now only quickly fixing the regression by a safe revert of all changes?

[lightmare]

I think the problem affects function declarations as well. If you replace the function expression in the example with a declaration, i.e. replace:

  for (const item of items) {
    await f(async (x) => {
      console.log(item);
    });
  }

with

  for (const item of items) {
    async function g(x) {
      console.log(item);
    }
    await f(g);
  }

the wrapper returned from _asyncToGenerator still cannot be cached in a function-scoped variable, because the wrapped function references a lexical.

[nicolo-ribaudo]

Ok let's revert this for now, we will reland with a proper fix later.

[nicolo-ribaudo]

Releasing, it will take 15 minutes

[liuxingbaoyu]

Thank you for your PR! I have a complete refactor locally and I will reopen a PR later.

[overlookmotel]

@liuxingbaoyu Just to flag that, depending on how you're refactoring, #15945 may also be similar - problem with temporary vars being function-scoped rather than block-scoped.