[ruby-core:102663] [Ruby master Bug#15608] What should be the correct output for Method#inspect with singleton methods?

Issue #15608 has been updated by usa (Usaku NAKAMURA).

Backport changed from 2.5: REQUIRED, 2.6: REQUIRED, 2.7: DONE to 2.5: REQUIRED, 2.6: DONE, 2.7: DONE

Backported into ruby_2_6 at r67902.

----------------------------------------
Bug #15608: What should be the correct output for Method#inspect with singleton methods?
https://bugs.ruby-lang.org/issues/15608#change-90657

* Author: Eregon (Benoit Daloze)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 2.6.1p33 (2019-01-30 revision 66950) [x86_64-linux]
* Backport: 2.5: REQUIRED, 2.6: DONE, 2.7: DONE
----------------------------------------
bug.rb:
```ruby
class C
  def foo
  end
end

obj = C.new

class << obj
  alias bar foo
end

p obj.method(:foo).owner
p obj.method(:foo)
raise unless obj.method(:foo).owner == C

p obj.method(:bar).owner
p obj.method(:bar)
raise unless obj.method(:bar).owner == obj.singleton_class
```

```
$ chruby 2.0.0
$ ruby -v bug.rb 
ruby 2.0.0p648 (2015-12-16) [x86_64-linux]
C
#<Method: C#foo>
#<Class:#<C:0x0055b39fcd2c30>>
#<Method: C(C)#foo>

$ chruby 2.3.8
$ ruby -v bug.rb 
ruby 2.3.8p459 (2018-10-18 revision 65136) [x86_64-linux]
C
#<Method: C#foo>
#<Class:#<C:0x000055668ebef268>>
#<Method: #<C:0x000055668ebef268>.bar(foo)>

$ chruby 2.4.5
$ ruby -v bug.rb 
ruby 2.4.5p335 (2018-10-18 revision 65137) [x86_64-linux]
C
#<Method: #<C:0x000055fdc99dc908>.foo>
#<Class:#<C:0x000055fdc99dc908>>
#<Method: #<C:0x000055fdc99dc908>.bar(foo)>

Same for 2.5.3 and 2.6.1
```

I think Method#inspect should show on which Module the method is defined (`Method#owner`), and only singleton methods should be shown as `receiver.method`, so:
```
C
#<Method: C#foo>
#<Class:#<C:0x000055668ebef268>>
#<Method: #<C:0x000055668ebef268>.bar(foo)>
```

Which only Ruby 2.3 does interestingly.

---

What's the meaning of the `C1(C2)` notation?

It seems to show `"#{receiver.class}(#{owner})` or `"#{receiver.singleton_class if receiver has a sclass}` depending on the version:
```ruby
class D < C
end
d = D.new
p d.method(:foo)
d.singleton_class
p d.method(:foo)
```

```
2.0-2.3:
#<Method: D(C)#foo>
#<Method: D(C)#foo>
2.4-2.6:
#<Method: D(C)#foo>
#<Method: #<D:0x000055c12b45e218>.foo>
```

I think the Ruby 2.4+ behavior is confusing and incorrect here, the object shouldn't be shown if it's not a singleton method, and Method#inspect shouldn't change for a given method.

Do you agree what I describe should be the correct behavior?
Can we fix it then?

---Files--------------------------------
method-inspect-15608.patch (2.31 KB)


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