[Meteor 3] Environment Variable Tweaks

[leonardoventurini]

Addresses these two issues:

#13112
#13113

1. No need to reset EV's value manually since ALS already handles it well by creating a new object every time.
2. Make sure the function's return value is preserved, WITHOUT enforcing a promise in the server.
3. Adjust the Client's withValue in dynamics_browser.js so it behaves similar to the server when handling promises.

meteor/packages/meteor/dynamics_browser.js

Line 49 in 08c2d7b

if (isPromise) {

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[denihs]

I think this will not work.

We need to wait for the func() to finish and reset the states of CURRENT_VALUE_KEY_NAME and UPPER_CALL_DYNAMICS_KEY_NAME after the func() is done.

This is because you can call a withValues inside another, and you need to set and reset those states to keep context between calls.

Otherwise, you'll get issues like this: #13063

[zodern]

#13063 changed it to create a new dynamics object each time instead of mutating the parent dynamics. This should remove the need to reset the state since the parent and children all have their own state. If you comment out the reset code, the example code from the PR description stills works correctly.

[leonardoventurini]

I agree with @zodern, I will include that code as a test just to make sure.

[zodern]

The meteor package could run in environments that have promises, but does not have Promise.finally. The promise package would polyfill it, but apps aren't required to use it.

[zodern]

One interesting side effect of this is tests now run inside a method.

Meteor 1/2 uses setImmediate to schedule running the tests, which does not preserve the environment. However, in Meteor 3 Async Local Storage does preserve the store value for the setImmediate callback.

I'm wondering if there should be a new api to run a function in a fresh environment. Meteor 1/2 supported this by simply creating a new fiber and running code inside it, or using the api variants that do not preserve the environment (setTimeout instead of Meteor.setTimeout, setImmediate instead of Meteor.setImmediate, etc.). Meteor 3 doesn't have any public api's to do the same.

[leonardoventurini]

@zodern This seems to work, what do you think?

a8edea4

52712ee

[zodern]

The implementation looks good. It probably should wrap this code or some other pat of the queue to maintain the behavior in Meteor 1/2 of not preserving the environment when running the queued tasks and so tests don't run inside a method.