object.c: Deprecate Object#=~ and add NilClass#=~`

Object#=~ always returns nil.  This behavior is not only unuseful but
also troublesome because it may hide a type error.

This change deprecates Object#=~.  For compatibility, NilClass#=~ is
newly introduced.  [Feature #15231]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65989 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -217,6 +217,12 @@ sufficient information, see the ChangeLog file or Redmine
     * NameError.new accepts +:receiver+ option to set receiver in Ruby
       code.  [Feature #14313]
 
+[NilClass]
+
+  [New methods]
+
+    * NilClass#=~ is added for compatibility.  [Feature #15231]
+
 [NoMethodError]
 
   [New options]
@@ -447,6 +453,10 @@ sufficient information, see the ChangeLog file or Redmine
     File.readlines do not invoke external commands even if the path starts
     with the pipe character <code>'|'</code>. [Feature #14245]
 
+[Object]
+
+  * Object#=~ is deprecated.  [Feature #15231]
+
 === Stdlib compatibility issues (excluding feature bug fixes)
 
 * These standard libraries have been promoted to default gems.

object.c

@@ -1479,6 +1479,19 @@ nil_inspect(VALUE obj)
     return rb_usascii_str_new2("nil");
 }
 
+/*
+ *  call-seq:
+ *     nil =~ other  -> nil
+ *
+ *  Dummy pattern matching -- always returns nil.
+ */
+
+static VALUE
+nil_match(VALUE obj1, VALUE obj2)
+{
+    return Qnil;
+}
+
 /***********************************************************************
  *  Document-class: TrueClass
  *
@@ -1673,6 +1686,7 @@ rb_false(VALUE obj)
 static VALUE
 rb_obj_match(VALUE obj1, VALUE obj2)
 {
+    rb_warning("Object#=~ is deprecated; it always returns nil");
     return Qnil;
 }
 
@@ -4149,6 +4163,7 @@ InitVM_Object(void)
     rb_define_method(rb_cNilClass, "to_a", nil_to_a, 0);
     rb_define_method(rb_cNilClass, "to_h", nil_to_h, 0);
     rb_define_method(rb_cNilClass, "inspect", nil_inspect, 0);
+    rb_define_method(rb_cNilClass, "=~", nil_match, 1);
     rb_define_method(rb_cNilClass, "&", false_and, 1);
     rb_define_method(rb_cNilClass, "|", false_or, 1);
     rb_define_method(rb_cNilClass, "^", false_xor, 1);

test/minitest/test_minitest_unit.rb

@@ -1528,7 +1528,9 @@ class TestMiniTestUnitTestCase < MiniTest::Unit::TestCase
 
   def test_refute_match_matcher_object
     @assertion_count = 2
-    @tc.refute_match Object.new, 5 # default #=~ returns false
+    non_verbose do
+      @tc.refute_match Object.new, 5 # default #=~ returns false
+    end
   end
 
   def test_refute_match_object_triggered