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stream: remove isPromise utility function #35925

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@aduh95 aduh95 commented Nov 2, 2020

The function was not checking if the parameter was actually a Promise
instance, but if it has a then method. Removing the utility function
in favor of a clearer typeof check, handling the case when the
thenable throws if then method is accessed more than once.

The difference between a thenable and a Promise may be important when using third party library (the parameter is provided by the user) and/or when Promise.prototype.then value is changed from userland.

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • commit message follows commit guidelines

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Review requested:

  • @nodejs/streams

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I'm not sure this is an improvement? The behavior is the same?

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aduh95 commented Nov 2, 2020

Yes the behavior is the same. Another way would be to change the name of the function isPromise -> isThenable.

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Actually the current implementation (and the one in this PR) is wrong if someone passes a thenable where then is a getter that throws the second time then is accessed.

It's not a big bug but promise test suites check for it.

The correct implementation would be to do it in "two steps":

  • First do const then = ret?.then
  • Then check if(typeof then === "function")
  • Then do then.call(ret, ...)

See here for an example

ronag added a commit to nodejs/undici that referenced this pull request Nov 2, 2020
The function was not checking if the parameter was actually a Promise
instance, but if it has a `then` method. Removing the utility function
in favor of a clearer `typeof` check, handling the case when the
thenable throws if then method is accessed more than once.
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aduh95 commented Nov 2, 2020

I've implemented the solution suggested by @benjamingr, PTAL.

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Please consider adding a test.

If you prefer not to - I'll add one sometime after this lands :]

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aduh95 commented Nov 3, 2020

Test added! It does fail on master and not with this PR, PTAL.

@ronag Have your concerns been addressed?

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aduh95 commented Nov 8, 2020

@ronag are you still blocking this or can your objection be dismissed?

@aduh95 aduh95 added the request-ci Add this label to start a Jenkins CI on a PR. label Nov 8, 2020
@github-actions github-actions bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Nov 8, 2020
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lgtm

@mcollina mcollina added the commit-queue Add this label to land a pull request using GitHub Actions. label Nov 9, 2020
@github-actions github-actions bot removed the commit-queue Add this label to land a pull request using GitHub Actions. label Nov 9, 2020
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github-actions bot commented Nov 9, 2020

Landed in adae822...ad98cf0

@github-actions github-actions bot closed this Nov 9, 2020
nodejs-github-bot pushed a commit that referenced this pull request Nov 9, 2020
The function was not checking if the parameter was actually a Promise
instance, but if it has a `then` method. Removing the utility function
in favor of a clearer `typeof` check, handling the case when the
thenable throws if then method is accessed more than once.

PR-URL: #35925
Reviewed-By: Robert Nagy <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
@aduh95 aduh95 deleted the stream-remove-isPromise branch November 9, 2020 08:32
danielleadams pushed a commit that referenced this pull request Nov 9, 2020
The function was not checking if the parameter was actually a Promise
instance, but if it has a `then` method. Removing the utility function
in favor of a clearer `typeof` check, handling the case when the
thenable throws if then method is accessed more than once.

PR-URL: #35925
Reviewed-By: Robert Nagy <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
@danielleadams danielleadams mentioned this pull request Nov 9, 2020
targos pushed a commit that referenced this pull request May 1, 2021
The function was not checking if the parameter was actually a Promise
instance, but if it has a `then` method. Removing the utility function
in favor of a clearer `typeof` check, handling the case when the
thenable throws if then method is accessed more than once.

PR-URL: #35925
Reviewed-By: Robert Nagy <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
@danielleadams danielleadams mentioned this pull request May 3, 2021
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5 participants