[ruby-core:105820] [Ruby master Feature#18137] A new method to check Proc is isolated or not

Issue #18137 has been updated by ko1 (Koichi Sasada).


I'm afraid that we can define "Isolated Proc".

As I know there are several versions.

1) self
a: self is shareable
b: self is not shareable

2) reference to outer scope variables
x: no references
y: has references, but read-only and values are fixed (if outer-scope variables are modified by other code, but keep to refer original values).
z: has references, but the variable storage is independent from outer-scope.

example of y:


```ruby
i = 1
pr = proc{
  p i #=> always 1
}
i = 2
pr.call #=> 1
```

example of z:

```ruby
i = 1
pr = proc{
  p i += 1
}
i += 10
pr.call #=> 2
```

----

From Ractor perspective, x and y are acceptable. for a and b,
Ractor doesn't care because the self will be replaced with `Ractor.new{}` and `define_method`. `Proc#call` is not allowed (!! Now it is allowed. BUG!! https://bugs.ruby-lang.org/issues/18243).



----------------------------------------
Feature #18137: A new method to check Proc is isolated or not
https://bugs.ruby-lang.org/issues/18137#change-94344

* Author: tagomoris (Satoshi TAGOMORI)
* Status: Open
* Priority: Normal
----------------------------------------
I want to check a Proc is isolated or not, like `Proc#isolated?`.

Proc objects are passed to libraries very often. For example, Rack web application is a callable (`respond_to(:call)`) object, and it may be a Proc.
When the library will call that Proc object in a Ractor, the passed Proc should be isolated by `Ractor.make_shareable()`. Otherwise, it causes RuntimeError.

So I want to check the Proc object is isolated or not earlier. It should be very helpful for library users because of the early and clear error messages.




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