UnboundMethod only refer defined_class

UnboundMethod records caller's class, like `D` or `E` on the
following case:

```ruby
class C
  def foo = :foo
end

class D < C
end

class E < C
end

d = D.instance_method(:foo)
e = E.instance_method(:foo)
```

But `d` and `e` only refers `C#foo` so that UnboundMethod doesn't
record `D` or `E`. This behavior changes the following methods:

* `UnboundMethod#inspect` (doesn't show caller's class)
* `UnboundMethod#==` (`d == e` for example)

fix https://bugs.ruby-lang.org/issues/18798

proc.c

@@ -1724,8 +1724,14 @@ mnew_internal(const rb_method_entry_t *me, VALUE klass, VALUE iclass,
 
     method = TypedData_Make_Struct(mclass, struct METHOD, &method_data_type, data);
 
-    RB_OBJ_WRITE(method, &data->recv, obj);
-    RB_OBJ_WRITE(method, &data->klass, klass);
+    if (obj == Qundef) {
+        RB_OBJ_WRITE(method, &data->recv, Qundef);
+        RB_OBJ_WRITE(method, &data->klass, Qundef);
+    }
+    else {
+        RB_OBJ_WRITE(method, &data->recv, obj);
+        RB_OBJ_WRITE(method, &data->klass, klass);
+    }
     RB_OBJ_WRITE(method, &data->iclass, iclass);
     RB_OBJ_WRITE(method, &data->owner, original_me->owner);
     RB_OBJ_WRITE(method, &data->me, me);
@@ -1876,9 +1882,9 @@ method_unbind(VALUE obj)
     method = TypedData_Make_Struct(rb_cUnboundMethod, struct METHOD,
                                    &method_data_type, data);
     RB_OBJ_WRITE(method, &data->recv, Qundef);
-    RB_OBJ_WRITE(method, &data->klass, orig->klass);
+    RB_OBJ_WRITE(method, &data->klass, Qundef);
     RB_OBJ_WRITE(method, &data->iclass, orig->iclass);
-    RB_OBJ_WRITE(method, &data->owner, orig->owner);
+    RB_OBJ_WRITE(method, &data->owner, orig->me->owner);
     RB_OBJ_WRITE(method, &data->me, rb_method_entry_clone(orig->me));
 
     return method;
@@ -3139,7 +3145,11 @@ method_inspect(VALUE method)
         defined_class = RBASIC_CLASS(defined_class);
     }
 
-    if (FL_TEST(mklass, FL_SINGLETON)) {
+    if (data->recv == Qundef) {
+        // UnboundMethod
+        rb_str_buf_append(str, rb_inspect(defined_class));
+    }
+    else if (FL_TEST(mklass, FL_SINGLETON)) {
         VALUE v = rb_ivar_get(mklass, attached);
 
         if (UNDEF_P(data->recv)) {

spec/ruby/core/method/unbind_spec.rb

@@ -27,8 +27,16 @@ describe "Method#unbind" do
       @string.should =~ /MethodSpecs::MyMod/
     end
 
-    it "returns a String containing the Module the method is referenced from" do
-      @string.should =~ /MethodSpecs::MySub/
+    ruby_version_is ""..."3.2" do
+      it "returns a String containing the Module the method is referenced from" do
+        @string.should =~ /MethodSpecs::MySub/
+      end
+    end
+
+    ruby_version_is "3.2" do
+      it "returns a String containing the Module the method is referenced from" do
+        @string.should =~ /MethodSpecs::MyMod/
+      end
     end
   end
 

spec/ruby/core/module/instance_method_spec.rb

@@ -45,10 +45,14 @@ describe "Module#instance_method" do
     @parent_um.inspect.should =~ /\bModuleSpecs::InstanceMeth\b/
     @child_um.inspect.should =~ /\bfoo\b/
     @child_um.inspect.should =~ /\bModuleSpecs::InstanceMeth\b/
-    @child_um.inspect.should =~ /\bModuleSpecs::InstanceMethChild\b/
+
     @mod_um.inspect.should =~ /\bbar\b/
     @mod_um.inspect.should =~ /\bModuleSpecs::InstanceMethMod\b/
-    @mod_um.inspect.should =~ /\bModuleSpecs::InstanceMethChild\b/
+
+    ruby_version_is ""..."3.2" do
+      @child_um.inspect.should =~ /\bModuleSpecs::InstanceMethChild\b/
+      @mod_um.inspect.should =~ /\bModuleSpecs::InstanceMethChild\b/
+    end
   end
 
   it "raises a TypeError if the given name is not a String/Symbol" do

spec/ruby/core/unboundmethod/equal_value_spec.rb

@@ -76,19 +76,38 @@ describe "UnboundMethod#==" do
     (@identical_body == @original_body).should == false
   end
 
-  it "returns false if same method but one extracted from a subclass" do
-    (@parent == @child1).should == false
-    (@child1 == @parent).should == false
+  ruby_version_is ""..."3.2" do
+    it "returns false if same method but one extracted from a subclass" do
+      (@parent == @child1).should == false
+      (@child1 == @parent).should == false
+    end
+
+    it "returns false if same method but extracted from two different subclasses" do
+      (@child2 == @child1).should == false
+      (@child1 == @child2).should == false
+    end
+
+    it "returns false if methods are the same but added from an included Module" do
+      (@includee == @includer).should == false
+      (@includer == @includee).should == false
+    end
   end
 
-  it "returns false if same method but extracted from two different subclasses" do
-    (@child2 == @child1).should == false
-    (@child1 == @child2).should == false
-  end
+  ruby_version_is "3.2" do
+    it "returns true if same method but one extracted from a subclass" do
+      (@parent == @child1).should == true
+      (@child1 == @parent).should == true
+    end
 
-  it "returns false if methods are the same but added from an included Module" do
-    (@includee == @includer).should == false
-    (@includer == @includee).should == false
+    it "returns false if same method but extracted from two different subclasses" do
+      (@child2 == @child1).should == true
+      (@child1 == @child2).should == true
+    end
+
+    it "returns true if methods are the same but added from an included Module" do
+      (@includee == @includer).should == true
+      (@includer == @includee).should == true
+    end
   end
 
   it "returns false if both have same Module, same name, identical body but not the same" do

spec/ruby/core/unboundmethod/shared/to_s.rb

@@ -20,12 +20,22 @@ describe :unboundmethod_to_s, shared: true do
   it "the String shows the method name, Module defined in and Module extracted from" do
     @from_module.send(@method).should =~ /\bfrom_mod\b/
     @from_module.send(@method).should =~ /\bUnboundMethodSpecs::Mod\b/
-    @from_method.send(@method).should =~ /\bUnboundMethodSpecs::Methods\b/
+
+    ruby_version_is ""..."3.2" do
+      @from_method.send(@method).should =~ /\bUnboundMethodSpecs::Methods\b/
+    end
   end
 
   it "returns a String including all details" do
-    @from_module.send(@method).should.start_with? "#<UnboundMethod: UnboundMethodSpecs::Methods(UnboundMethodSpecs::Mod)#from_mod"
-    @from_method.send(@method).should.start_with? "#<UnboundMethod: UnboundMethodSpecs::Methods(UnboundMethodSpecs::Mod)#from_mod"
+    ruby_version_is ""..."3.2" do
+      @from_module.send(@method).should.start_with? "#<UnboundMethod: UnboundMethodSpecs::Methods(UnboundMethodSpecs::Mod)#from_mod"
+      @from_method.send(@method).should.start_with? "#<UnboundMethod: UnboundMethodSpecs::Methods(UnboundMethodSpecs::Mod)#from_mod"
+    end
+
+    ruby_version_is "3.2" do
+      @from_module.send(@method).should.start_with? "#<UnboundMethod: UnboundMethodSpecs::Mod#from_mod"
+      @from_method.send(@method).should.start_with? "#<UnboundMethod: UnboundMethodSpecs::Mod#from_mod"
+    end
   end
 
   it "does not show the defining module if it is the same as the origin" do

test/ruby/test_method.rb

@@ -1236,12 +1236,12 @@ class TestMethod < Test::Unit::TestCase
     unbound = b.instance_method(:foo)
 
     assert_equal unbound, b.public_instance_method(:foo)
-    assert_equal "#<UnboundMethod: B(A)#foo(arg=...) #{__FILE__}:#{line}>", unbound.inspect
+    assert_equal "#<UnboundMethod: A#foo(arg=...) #{__FILE__}:#{line}>", unbound.inspect
     assert_equal [[:opt, :arg]], unbound.parameters
 
     a.remove_method(:foo)
 
-    assert_equal "#<UnboundMethod: B(A)#foo(arg=...) #{__FILE__}:#{line}>", unbound.inspect
+    assert_equal "#<UnboundMethod: A#foo(arg=...) #{__FILE__}:#{line}>", unbound.inspect
     assert_equal [[:opt, :arg]], unbound.parameters
 
     obj = b.new
@@ -1281,7 +1281,7 @@ class TestMethod < Test::Unit::TestCase
 
     a.remove_method(:foo)
 
-    assert_equal "#<UnboundMethod: B(A)#foo(arg=...) #{__FILE__}:#{line}>", unbound.inspect
+    assert_equal "#<UnboundMethod: A#foo(arg=...) #{__FILE__}:#{line}>", unbound.inspect
     assert_equal [[:opt, :arg]], unbound.parameters
     assert_equal a0_foo, unbound.super_method
 
@@ -1289,7 +1289,7 @@ class TestMethod < Test::Unit::TestCase
     assert_equal 1, unbound.bind_call(obj)
 
     assert_include b.instance_methods(false), :foo
-    assert_equal "#<UnboundMethod: B(A0)#foo(arg1=..., arg2=...) #{__FILE__}:#{line0}>", b.instance_method(:foo).inspect
+    assert_equal "#<UnboundMethod: A0#foo(arg1=..., arg2=...) #{__FILE__}:#{line0}>", b.instance_method(:foo).inspect
   end
 
   def test_zsuper_method_redefined_bind_call