Flow: Potentially unsafe get/set usage warning

[pronebird]

I've got this strange warning:

[flow] [flow] Potentially unsafe get/set usage (Getters and setters with side effects are potentially >unsafe and disabled by default. You may opt-in to using them anyway by putting >unsafe.enable_getters_and_setters=true into the [options] section of your .flowconfig.)

Can you clarify what kind of side-effects my plain setter/getter cause?

// @flow
class Git {

  constructor(path: string) {
    this.gitBinary = 'git';
    this._path = path;
  }

  get path(): string {
    return this._path;
  }

  set path(path: string) {
    throw new Error('Path is readonly.');
  }

  get gitBinary(): string {
    return this._gitBinary;
  }

  set gitBinary(value: string) {
    this._gitBinary = value;
  }

}

[vkurchatkin]

Well, your example is entirely invalid, because you try to set this.path, but don't have a setter, and in getter you cause infinite recursion.

[pronebird]

@vkurchatkin yeah right. So I back my properties with some private variable, still get the same warning.

[pronebird]

It does not really matter how I define properties, even simple getter that returns constant still emits warning.

class Git {

  static get master() {
    return 'master';
  }

}

[vkurchatkin]

I'm not 100% sure, but I think Flow always warns about this, because getter or setter with side effects can potentially invalidate type refinements, but Flow doesn't actually check if your getter/setter has side effects

[mourner]

So Flow considers all setters/getters as an error regardless of their implementation? That's pretty frustrating.

[rsolomon]

If you prefer to use them without the warnings, you can opt to enable the feature using the configuration option listed in the warning message: unsafe.enable_getters_and_setters=true

[jdalegonzalez]

It would be nice to disable the warning on a per getter/setter basis. That way, a human could evaluate whether or not a particular getter/setter had side-effects as opposed to blanket acceptance.

[danawoodman]

This seems like a pretty clear bug in Flow... Any plans on getting getters/setters working in Flow without having to pass in unsafe flags? It seems that is a bad idea since flow could actually catch issues rather than just completely ignoring getters/setters...

[dhmacs]

@jdalegonzalez I think you can use // $FlowFixMe right above the getter to suppress the error

[yoiang]

Unfortunately // $FlowFixMe disables all checks vs. enabling only unsafe.enable_getters_and_setters for that line as an interim workaround until Flow can understand side effects.

[thornjad]

Is there any movement on this? From my perspective, this is a pretty big bug in that Flow essentially doesn't work for setters and getters.

[agrcrobles]

Waw! Looks like it fixed in the latest version of flow, see working example

[fsarron-nexway]

@agrcrobles seem to not complain n any selected version in this example

[AdamDanielKing]

@agrcrobles Still having the issue on 0.63.1. Edit: Never mind. I forgot Nuclide uses the globally installed flow binary.

[TrySound]

@Adam0000 What's an issue? And show your flowconfig

[pronebird]

As mentioned by @fsarron-nexway flow.org/try doesn't complain about this error in any of versions of Flow

[augbog]

Sounds like this no longer happens -- also upgraded flow and don't see the issue anymore. Feel free to close.

[pronebird]

Closing since v0.64 seems to address this for me.

Also unsafe.enable_getters_and_setters is now removed from Flow config.