[ruby-core:98790] [Ruby master Bug#16959] Weakmap has specs and third-party usage despite being a private API

Issue #16959 has been updated by headius (Charles Nutter).


Please don't edit my description.

I personally do not believe the specs should be removed. But I also do not feel that WeakMap is the right abstraction. If Weakref had support for a reference queue, then WeakMap would be a pure-Ruby library that all implementations could share. Further, there would not just be the one WeakMap... Users could build their own weak arrays and other data structures. What I am asking for here is that we don't just accept this private API as official public API without going through the process that every other API must go through. This API was never discussed for public use, and has limitations that could be addressed quickly by making Weakref a bit more robust.

The bottom line is that WeakMap was added as a private API to make Weakref work better, but was never discussed and approved to become a public API. Yes, people have been using it, and that's not good. Yes, those uses predate the recent specs, but the specs and the 2.7 changelog make it even more likely this will become a de facto standard API, completely circumventing all processes for adding public APIs.

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Bug #16959: Weakmap has specs and third-party usage despite being a private API
https://bugs.ruby-lang.org/issues/16959#change-86149

* Author: headius (Charles Nutter)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
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Weakmap is still described as an internal API, and the documentation points users at WeakRef as the official public API:

https://github.com/ruby/ruby/blob/1fb16dbb6e28b9f32f92554d29e646e088b21a98/gc.c#L11928-L11936

However there are now specs for its current set of features, even though those features have never been discussed or approved as a public API:

https://github.com/ruby/spec/tree/dd8437628a6f2de5b74b338d4960682bb1590a60/core/objectspace/weakmap

And we are starting to see it being used by the community:

* https://github.com/jruby/jruby/issues/6267
* https://github.com/rsim/oracle-enhanced/issues/2027 
* https://github.com/rails/rails/pull/39121

One of two things needs to happen:

* Weakmap is made a public API after some discussion. It would be an official public feature only in 2.8/3.0 or higher.
* ~~The specs are be removed and Weakmap remains a private API not to be used by the community. I suspect the addition of the specs led to folks starting to use this private API.~~

(edit: The Rails PR was merged after the specs, but the change is actually a year old, as mentioned below. In any case there's plenty of in-the-wild uses of WeakMap that go back even further.)

Personally, I'm in much more in favor of making WeakRef support all the features necessary to implement Weakmap in pure Ruby, rather than the other way around:

https://bugs.ruby-lang.org/issues/6309

But whatever happens it needs to happen soon, since this use case is now a merged feature in Rails master.



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