[Bug #18937] Coerce non-Numeric into Complex at comparisons

complex.c

@@ -1121,7 +1121,10 @@ nucomp_real_p(VALUE self)
 static VALUE
 nucomp_cmp(VALUE self, VALUE other)
 {
-    if (nucomp_real_p(self) && k_numeric_p(other)) {
+    if (!k_numeric_p(other)) {
+        return rb_num_coerce_cmp(self, other, idCmp);
+    }
+    if (nucomp_real_p(self)) {
         if (RB_TYPE_P(other, T_COMPLEX) && nucomp_real_p(other)) {
             get_dat2(self, other);
             return rb_funcall(adat->real, idCmp, 1, bdat->real);

test/ruby/test_complex.rb

@@ -579,7 +579,7 @@ class Complex_Test < Test::Unit::TestCase
 
   def test_coerce2
     x = ObjectX.new
-    %w(+ - * / quo **).each do |op|
+    %w(+ - * / quo ** <=>).each do |op|
       assert_kind_of(Numeric, Complex(1).__send__(op, x))
     end
   end