Don't display singleton class in Method#inspect unless method defined…

… there

Previously, if an object has a singleton class, and you call
Object#method on the object, the resulting string would include
the object's singleton class, even though the method was not
defined in the singleton class.

Change this so the we only show the singleton class if the method
is defined in the singleton class.

Fixes [Bug #15608]

(cherry picked from commit e02bd0e)

proc.c

@@ -2804,7 +2804,8 @@ method_inspect(VALUE method)
     TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);
     str = rb_sprintf("#<% "PRIsVALUE": ", rb_obj_class(method));
 
-    mklass = data->klass;
+    mklass = data->iclass;
+    if (!mklass) mklass = data->klass;
 
     if (RB_TYPE_P(mklass, T_ICLASS)) {
         /* TODO: I'm not sure why mklass is T_ICLASS.
@@ -2844,6 +2845,12 @@ method_inspect(VALUE method)
 	}
     }
     else {
+        mklass = data->klass;
+        if (FL_TEST(mklass, FL_SINGLETON)) {
+            do {
+               mklass = RCLASS_SUPER(mklass);
+            } while (RB_TYPE_P(mklass, T_ICLASS));
+        }
 	rb_str_buf_append(str, rb_inspect(mklass));
 	if (defined_class != mklass) {
 	    rb_str_catf(str, "(% "PRIsVALUE")", defined_class);

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

@@ -31,4 +31,22 @@
   it "returns a String containing the Module the method is referenced from" do
     @string.should =~ /MethodSpecs::MySub/
   end
+
+  ruby_version_is '2.8' do
+    it "returns a String containing the Module containing the method if object has a singleton class but method is not defined in the singleton class" do
+      obj = MethodSpecs::MySub.new
+      obj.singleton_class
+      @m = obj.method(:bar)
+      @string = @m.send(@method).sub(/0x\w+/, '0xXXXXXX')
+      @string.should =~ /\A#<Method: MethodSpecs::MySub\(MethodSpecs::MyMod\)#bar\(\) /
+    end
+  end
+
+  it "returns a String containing the singleton class if method is defined in the singleton class" do
+    obj = MethodSpecs::MySub.new
+    def obj.bar; end
+    @m = obj.method(:bar)
+    @string = @m.send(@method).sub(/0x\w+/, '0xXXXXXX')
+    @string.should =~ /\A#<Method: #<MethodSpecs::MySub:0xXXXXXX>\.bar/
+  end
 end

test/ruby/test_method.rb

@@ -459,6 +459,14 @@ def o.foo; end; line_no = __LINE__
     c3.class_eval { alias bar foo }
     m3 = c3.new.method(:bar)
     assert_equal("#<Method: #{c3.inspect}(#{c.inspect})#bar(foo)() #{__FILE__}:#{line_no}>", m3.inspect, bug7806)
+
+    bug15608 = '[ruby-core:91570] [Bug #15608]'
+    c4 = Class.new(c)
+    c4.class_eval { alias bar foo }
+    o = c4.new
+    o.singleton_class
+    m4 = o.method(:bar)
+    assert_equal("#<Method: #{c4.inspect}(#{c.inspect})#bar(foo)() #{__FILE__}:#{line_no}>", m4.inspect, bug15608)
   end
 
   def test_callee_top_level