Set operations retain compare_by_identity flag on 4.0

Set#&, #classify, #divide, #flatten, #flatten! and #map! keep the
receiver's compare_by_identity flag since the fix for [Bug #22174]
was backported to Ruby 4.0 (4.0.8).
See https://bugs.ruby-lang.org/issues/22174

Same as the specs from ruby/ruby#18848, with the "4.1" guards
changed to "4.0" for the backport.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: mrhoribu

core/set/classify_spec.rb

@@ -24,9 +24,19 @@
     classified.should == { 3 => Set["one", "two"], 4 => Set["four"], 5 => Set["three"] }
   end
 
-  it "does not retain compare_by_identity flag" do
-    set = Set["one", "two"].compare_by_identity
-    classified = set.classify { |x| x.length }
-    classified.values.each { |s| s.compare_by_identity?.should == false }
+  ruby_version_is "4.0" do
+    it "retains compare_by_identity flag" do
+      set = Set["one", "two"].compare_by_identity
+      classified = set.classify { |x| x.length }
+      classified.values.each { |s| s.compare_by_identity?.should == true }
+    end
+  end
+
+  ruby_version_is ""..."4.0" do
+    it "does not retain compare_by_identity flag" do
+      set = Set["one", "two"].compare_by_identity
+      classified = set.classify { |x| x.length }
+      classified.values.each { |s| s.compare_by_identity?.should == false }
+    end
   end
 end

core/set/divide_spec.rb

@@ -18,10 +18,20 @@
     ret.each(&:even?).should == Set[Set[1, 3], Set[2, 4]]
   end
 
-  it "does not retain compare_by_identity flag" do
-    set = Set["one", "two"].compare_by_identity
-    res = set.divide { |x| x.length }
-    res.each { |s| s.compare_by_identity?.should == false }
+  ruby_version_is "4.0" do
+    it "retains compare_by_identity flag" do
+      set = Set["one", "two"].compare_by_identity
+      res = set.divide { |x| x.length }
+      res.each { |s| s.compare_by_identity?.should == true }
+    end
+  end
+
+  ruby_version_is ""..."4.0" do
+    it "does not retain compare_by_identity flag" do
+      set = Set["one", "two"].compare_by_identity
+      res = set.divide { |x| x.length }
+      res.each { |s| s.compare_by_identity?.should == false }
+    end
   end
 end
 

core/set/flatten_spec.rb

@@ -16,17 +16,24 @@
     -> { set.flatten }.should.raise(ArgumentError)
   end
 
+  ruby_version_is "4.0" do
+    it "retains compare_by_identity flag" do
+      set = Set[1, 2, Set[3, 4]].compare_by_identity
+      set.flatten.compare_by_identity?.should == true
+    end
+  end
+
   ruby_version_is ""..."4.0" do
     context "when Set contains a Set-like object" do
       it "returns a copy of self with each included Set-like object flattened" do
         Set[SetSpecs::SetLike.new([1])].flatten.should == Set[1]
       end
     end
-  end
 
-  it "does not retain compare_by_identity flag" do
-    set = Set[1, 2, Set[3, 4]].compare_by_identity
-    set.flatten.compare_by_identity?.should == false
+    it "does not retain compare_by_identity flag" do
+      set = Set[1, 2, Set[3, 4]].compare_by_identity
+      set.flatten.compare_by_identity?.should == false
+    end
   end
 end
 
@@ -52,10 +59,20 @@
     -> { set.flatten! }.should.raise(ArgumentError)
   end
 
-  it "does not retain compare_by_identity flag when flattening elements" do
-    set = Set[1, 2, Set[3, 4]].compare_by_identity
-    set.flatten!
-    set.compare_by_identity?.should == false
+  ruby_version_is "4.0" do
+    it "retains compare_by_identity flag when flattening elements" do
+      set = Set[1, 2, Set[3, 4]].compare_by_identity
+      set.flatten!
+      set.compare_by_identity?.should == true
+    end
+  end
+
+  ruby_version_is ""..."4.0" do
+    it "does not retain compare_by_identity flag when flattening elements" do
+      set = Set[1, 2, Set[3, 4]].compare_by_identity
+      set.flatten!
+      set.compare_by_identity?.should == false
+    end
   end
 
   it "retains compare_by_identity flag if no elements are flattened" do

core/set/intersection_spec.rb

@@ -21,9 +21,19 @@
     -> { @set & Object.new }.should.raise(ArgumentError)
   end
 
-  it "does not retain compare_by_identity flag" do
-    @set.compare_by_identity
-    (@set & Set[:b, :c, :d, :e]).compare_by_identity?.should == false
-    (@set & [:b, :c, :d]).compare_by_identity?.should == false
+  ruby_version_is "4.0" do
+    it "retains compare_by_identity flag" do
+      @set.compare_by_identity
+      (@set & Set[:b, :c, :d, :e]).compare_by_identity?.should == true
+      (@set & [:b, :c, :d]).compare_by_identity?.should == true
+    end
+  end
+
+  ruby_version_is ""..."4.0" do
+    it "does not retain compare_by_identity flag" do
+      @set.compare_by_identity
+      (@set & Set[:b, :c, :d, :e]).compare_by_identity?.should == false
+      (@set & [:b, :c, :d]).compare_by_identity?.should == false
+    end
   end
 end

core/set/map_spec.rb

@@ -20,9 +20,19 @@
     @set.should == Set[2, 4, 6, 8, 10]
   end
 
-  it "does not retain compare_by_identity flag" do
-    @set.compare_by_identity
-    @set.map! { |x| x * 2 }
-    @set.compare_by_identity?.should == false
+  ruby_version_is "4.0" do
+    it "retains compare_by_identity flag" do
+      @set.compare_by_identity
+      @set.map! { |x| x * 2 }
+      @set.compare_by_identity?.should == true
+    end
+  end
+
+  ruby_version_is ""..."4.0" do
+    it "does not retain compare_by_identity flag" do
+      @set.compare_by_identity
+      @set.map! { |x| x * 2 }
+      @set.compare_by_identity?.should == false
+    end
   end
 end