Disabling privacy for testing

[sigmundch]

It would be very useful to have some mechanism to test private members without having to expose them in a library.

One option is to add a flag to allow access to private members, for instance:
'--disable_privacy'

The semantics could be either:
(a) all imports now export all names (including private names) to the imported library.
(b) only the imports of the initial script have this semantics (so tests can see internals of the libraries it imports, but the rest of the code wont have to worry about name collisions).

This requires changes in both the VM and frog. I'm arbitrarily labeling this bug with the frog area because I can't mark both.

This would be a test case that should work:
mysource.dart:
  #library("mysource");
  get _fooForTesting() => 1;

mytest.dart:
  #import("mysource.dart");
  main() => Expect.equals(1, _fooForTesting);

---

dart --disable_privacy mytest.dart should pass.

[anders-sandholm]

Removed Area-Frog label.
Added Area-Dart2JS, FromAreaFrog labels.

[kasperl]

Removed Type-Defect, Priority-Medium, FromAreaFrog labels.
Added Type-Enhancement, Priority-Low labels.

[kasperl]

Added this to the Later milestone.

[kasperl]

Removed this from the Later milestone.

[kasperl]

Added this to the Later milestone.

[kasperl]

Removed Priority-Low label.
Added Priority-Medium label.

[kasperl]

Added TriageForM5 label.

[kasperl]

Removed TriageForM5 label.

[kasperl]

Removed this from the Later milestone.
Added Oldschool-Milestone-Later label.

[kasperl]

Removed Oldschool-Milestone-Later label.

[floitschG]

Reassigning to language.
I fully agree that a way to access private state during testing would be extremely useful.

---

Removed Area-Dart2JS label.
Added Area-Language label.

[gbracha]

Issue #10219 has been merged into this issue.

[rmacnak-google]

Mirrors can be used to bypass library privacy.

[floitschG]

That doesn't work on Flutter, dart2js, ... and is extremely painful.

[eernstg]

For reflectable, a programmatic privacy override mechanism would be very useful as well.

[michaelcarter-wf]

+1 for a way to turn off privacy in tests.

[jtmcdole]

import 'dart:mirrors';

class Foo {
int _privateInt = 12;
}
...
var inst = reflect(new Foo());
print(inst.getField(#_privateInt).reflectee); // 12

[jtmcdole]

Scratch that; doesn't work across libraries.

+1 for a way to turn off privacy :)

[zoechi]

It was mentioned in discussions to introduce something like friend libraries which are allowed to access each others private members also as a possible replacement for part / part of. I'm not sure how this would work out for all use cases.
Anyway I also think there should be a way around this limitation.

[lrhn]

Just "turning off" privacy is not going to work. That would make "_foo" in two different libraries suddenly conflict or override each other, so some code will just fail to work - or even compile. Private names is a way to avoid having to invent unique names as much as it's a way of restricting access.

I highly recommend not using privacy for things you want to test. Instead move them to a separate helper library where they are public, and run tests against that library. Then export only the parts you need in the real library.
That won't work for private members of public classes, but if you assume the presence of private fields or methods, then your tests are not refactoring-safe. Changing the name of a private member should be a completely invisible change. Testing the public methods should be sufficient to test that a class actually behaves as it should. If you have functionality that you want to test independently of the class API, then that functionality is likely a good choice for moving into static helper functions that can actually be tested independently.

(In other words: If you think you need access to private stuff, consider redesigning your class and library layout to not need it any more).

[rmacnak-google]

@jtmcdole To do it across libraries, you need to get the private symbol with respect to the library you're trying to access.

class Foo {
int _privateInt = 12;
}
...
var inst = reflect(new Foo());
var sym = MirrorSystem.getSymbol('_privateInt', inst.type.owner);
print(inst.getField(sym).reflectee); // 12

[jtmcdole]

@rmacnak-google, yep, I found that out via a different method and it isn't too messy. I like the type.owner though. Just wish there was a ways to still use #_privateInt in that expression.

[lrhn]

You can't use #_privateInt because it's the private name belonging to your library. It's a completely different name than one with similar syntax in a different library.

[zoechi]

Related #22841

[zoechi]

#28273 seems to be the chosen approach. Can this issue be closed?