[ruby-core:107572] [Ruby master Bug#18582] Hash.group_by not grouping correctly with SortedSets

Issue #18582 has been updated by [e-mail] (Mike Carlton).


Ah, I had tried method_defined?, but it returns true (for inherited Kernel#eql?)

I did not realized that method_defined? also accepted a inherited=false argument.

Thank you.

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Bug #18582: Hash.group_by not grouping correctly with SortedSets
https://bugs.ruby-lang.org/issues/18582#change-96484

* Author: [e-mail] (Mike Carlton)
* Status: Third Party's Issue
* Priority: Normal
* ruby -v: ruby 3.0.3p157 (2021-11-24 revision 3fb7d2cadc) [x86_64-darwin20]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
With Ruby 3.0.3, when using SortedSets as group_by value for Hash, equal SortedSets are not grouped as they should be.
This works correctly in Ruby 2.7.1 (when rbtree gem is not present, not tested with rbtree gem)

This works correctly using Sets as the group_by value in both 2.7.1 and 3.0.3

This test code:
```ruby
require 'set'
require 'sorted_set' if RUBY_VERSION > '3'

puts RUBY_VERSION

# works when keys are Sets
s1 = Set['fubar']
s2 = Set['fubar']
warn "expected #{s1} to equal #{s2}" unless s1 == s2

grouped = { 'a' => s1, 'b' => s2 }.group_by { |_, v| v }
puts "grouped by Sets: #{grouped}"
warn "expected 1 key in hash grouped by Sets, got #{grouped.keys.size}" unless grouped.keys.size == 1

# 3.0.3 fails when keys are SortdSets
ss1 = SortedSet['fubar']
ss2 = SortedSet['fubar']
warn "expected #{ss1} to equal #{ss2}" unless ss1 == ss2

grouped = { 'a' => ss1, 'b' => ss2 }.group_by { |_, v| v }
puts "grouped by SortedSets: #{grouped}"
warn "expected 1 key in hash grouped by SortedSets, got #{grouped.keys.size}" unless grouped.keys.size == 1
```
prints this under 2.7.1:
```
2.7.1
grouped by Sets: {#<Set: {"fubar"}>=>[["a", #<Set: {"fubar"}>], ["b", #<Set: {"fubar"}>]]}
grouped by SortedSets: {#<SortedSet: {"fubar"}>=>[["a", #<SortedSet: {"fubar"}>], ["b", #<SortedSet: {"fubar"}>]]}
```

but prints this under 3.0.3:
```
3.0.3
grouped by Sets: {#<Set: {"fubar"}>=>[["a", #<Set: {"fubar"}>], ["b", #<Set: {"fubar"}>]]}
grouped by SortedSets: {#<SortedSet: {"fubar"}>=>[["a", #<SortedSet: {"fubar"}>]], #<SortedSet: {"fubar"}>=>[["b", #<SortedSet: {"fubar"}>]]}
expected 1 key in hash grouped by SortedSets, got 2
```



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