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Promisify breaks resolve #151

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Promisify breaks resolve#151

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@reggi
reggi
opened on Feb 22, 2018

I have an example of tests passing (can't publish at the moment) with require.resolve and with resolve as a callback, but when I wrap resolve in const resolveAsync = Promise.promisify(resolve) for some reason the tests that worked are failing. I've also implemented my own wrapped promise and some of tests pass, and others fail, specifically cases where there's a package.json resolve.

Any ideas why this package is un-promisify-able, and potential ways around it?

Activity

  1. ljharb commented on Feb 22, 2018

    @ljharb
    ljharb
    on Feb 22, 2018
    Member

    What promisify implementation are you using?

    Since https://npmjs.com/util.promisify is built into node, that’s really the only implementation that matters.

    If resolve can’t promisify by default, we could maybe add a custom promisify symbol.

    Does it work with the canonical implementation?

  2. reggi commented on Feb 22, 2018

    @reggi
    reggi
    on Feb 22, 2018
    Author

    I've been using Bluebird to promisify, but even an initial check here.

    ➜  ~ trymodule util.promisify resolve
Gonna start a REPL with packages installed and loaded for you
'util.promisify' was already installed since before!
'resolve' was already installed since before!
Package 'util.promisify' was loaded and assigned to 'util_promisify' in the current scope
Package 'resolve' was loaded and assigned to 'resolve' in the current scope
REPL started...
> require.resolve('./Desktop/jest-example/index.js')
'/Users/treggi/Desktop/jest-example/index.js'
> util.promisify(resolve)('./Desktop/jest-example/index.js').then(console.log)
Promise {
  <pending>,
  domain:
   Domain {
     domain: null,
     _events: { error: [Function: debugDomainError] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] } }
> (node:86567) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Cannot find module './Desktop/jest-example/index.js' from 'internal'
(node:86567) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

    Running node 9.5

  3. ljharb commented on Feb 23, 2018

    @ljharb
    ljharb
    on Feb 23, 2018
    Member

    Unhandled promise rejection (rejection id: 1): Error: Cannot find module './Desktop/jest-example/index.js' from 'internal' - it seems like it's properly rejecting. Try adding .catch(e => console.error(e))?

  4. reggi commented on Feb 23, 2018

    @reggi
    reggi
    on Feb 23, 2018 via email
    Author

  5. ljharb commented on Feb 23, 2018

    @ljharb
    ljharb
    on Feb 23, 2018
    Member

    What happens with a non-promisified version of this module, however?

  6. reggi commented on Feb 23, 2018

    @reggi
    reggi
    on Feb 23, 2018
    Author

    @ljharb It works perfectly fine

    Let me explain this example:

    ➜  ~ trymodule util.promisify resolve
Gonna start a REPL with packages installed and loaded for you
'util.promisify' was already installed since before!
'resolve' was already installed since before!
Package 'util.promisify' was loaded and assigned to 'util_promisify' in the current scope
Package 'resolve' was loaded and assigned to 'resolve' in the current scope
REPL started...

    Regular require.resolve works, and resolves this path.

    > require.resolve('./Desktop/jest-example/index.js')
'/Users/treggi/Desktop/jest-example/index.js'

    The resolve module callback returns the correct resolved path.

    > resolve('./Desktop/jest-example/index.js', (err, value) => console.log(value))
undefined
> /Users/treggi/Desktop/jest-example/index.js

    Node 9's native util.promisify returns a promise, calls it's .catch and logs the error.

    > util.promisify(resolve)('./Desktop/jest-example/index.js').then(console.log).catch(e => console.log(e))
Promise {
  <pending>,
  domain:
   Domain {
     domain: null,
     _events: { error: [Function: debugDomainError] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] } }
> { Error: Cannot find module './Desktop/jest-example/index.js' from 'internal'
    at /Users/treggi/.trymodule/node_modules/resolve/lib/async.js:61:35
    at load (/Users/treggi/.trymodule/node_modules/resolve/lib/async.js:80:43)
    at onex (/Users/treggi/.trymodule/node_modules/resolve/lib/async.js:105:17)
    at /Users/treggi/.trymodule/node_modules/resolve/lib/async.js:26:73
    at FSReqWrap.oncomplete (fs.js:166:21) code: 'MODULE_NOT_FOUND' }

    The util.promisify module returns a promise, calls it's .catch and logs the error.

    > util_promisify(resolve)('./Desktop/jest-example/index.js').then(console.log).catch(e => console.log(e))
Promise {
  <pending>,
  domain:
   Domain {
     domain: null,
     _events: { error: [Function: debugDomainError] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] } }
> { Error: Cannot find module './Desktop/jest-example/index.js' from 'internal'
    at /Users/treggi/.trymodule/node_modules/resolve/lib/async.js:61:35
    at load (/Users/treggi/.trymodule/node_modules/resolve/lib/async.js:80:43)
    at onex (/Users/treggi/.trymodule/node_modules/resolve/lib/async.js:105:17)
    at /Users/treggi/.trymodule/node_modules/resolve/lib/async.js:26:73
    at FSReqWrap.oncomplete (fs.js:166:21) code: 'MODULE_NOT_FOUND' }

  7. reggi commented on Feb 24, 2018

    @reggi
    reggi
    on Feb 24, 2018
    Author

    Any idea what's going on here @ljharb?

  8. ljharb commented on Feb 24, 2018

    @ljharb
    ljharb
    on Feb 24, 2018
    Member

    @reggi what happens if you call the promisified resolve with an empty object as the second argument?

  9. ljharb commented on Feb 24, 2018

    @ljharb
    ljharb
    on Feb 24, 2018
    Member

    After looking into this a bit more, the issue is that the assumption that "promisify will work on everything" is flawed; it won't.

    Using util.promisfy.custom, we could provide a custom implementation that would work with the native one (but not with bluebird) - but then this module would have to add a dependency on util.promisify and/or restrict which node versions it runs on.

    In other words, I think the proper solution is to wrap resolve in new Promise if you want to promisify it.

  10. ljharb
    closed this as completedon Feb 24, 2018
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