Handle zero-like imaginary part as zero in to_r (#9581)

Fixes [Bug #5179]

complex.c

@@ -1841,9 +1841,11 @@ nucomp_to_f(VALUE self)
  *
  *   Complex.rect(1, 0).to_r              # => (1/1)
  *   Complex.rect(1, Rational(0, 1)).to_r # => (1/1)
+ *   Complex.rect(1, 0.0).to_r            # => (1/1)
  *
  * Raises RangeError if <tt>self.imag</tt> is not exactly zero
- * (either <tt>Integer(0)</tt> or <tt>Rational(0, _n_)</tt>).
+ * (either <tt>Integer(0)</tt> or <tt>Rational(0, _n_)</tt>)
+ * and <tt>self.imag.to_r</tt> is not exactly zero.
  *
  * Related: Complex#rationalize.
  */
@@ -1852,10 +1854,16 @@ nucomp_to_r(VALUE self)
 {
     get_dat1(self);
 
-    if (!k_exact_zero_p(dat->imag)) {
+    if (RB_FLOAT_TYPE_P(dat->imag) && FLOAT_ZERO_P(dat->imag)) {
+        /* Do nothing here */
+    }
+    else if (!k_exact_zero_p(dat->imag)) {
+        VALUE imag = rb_check_convert_type_with_id(dat->imag, T_RATIONAL, "Rational", idTo_r);
+        if (NIL_P(imag) || !k_exact_zero_p(imag)) {
             rb_raise(rb_eRangeError, "can't convert %"PRIsVALUE" into Rational",
                      self);
         }
+    }
     return f_to_r(dat->real);
 }
 

spec/ruby/core/complex/to_r_spec.rb

@@ -34,8 +34,16 @@ describe "Complex#to_r" do
   end
 
   describe "when the imaginary part is Float 0.0" do
+    ruby_version_is ''...'3.4' do
       it "raises RangeError" do
         -> { Complex(0, 0.0).to_r }.should raise_error(RangeError)
       end
     end
+
+    ruby_version_is '3.4' do
+      it "returns a Rational" do
+        Complex(0, 0.0).to_r.should == 0r
+      end
+    end
+  end
 end

test/ruby/test_complex.rb

@@ -1054,6 +1054,29 @@ class Complex_Test < Test::Unit::TestCase
     assert_raise(RangeError){Rational(Complex(3,2))}
   end
 
+  def test_to_r_with_float
+    assert_equal(Rational(3), Complex(3, 0.0).to_r)
+    assert_raise(RangeError){Complex(3, 1.0).to_r}
+  end
+
+  def test_to_r_with_numeric_obj
+    c = Class.new(Numeric)
+
+    num = 0
+    c.define_method(:to_s) { num.to_s }
+    c.define_method(:==) { num == it }
+    c.define_method(:<)  { num <  it }
+
+    o = c.new
+    assert_equal(Rational(3), Complex(3, o).to_r)
+
+    num = 1
+    assert_raise(RangeError){Complex(3, o).to_r}
+
+    c.define_method(:to_r) { 0r }
+    assert_equal(Rational(3), Complex(3, o).to_r)
+  end
+
   def test_to_c
     c = nil.to_c
     assert_equal([0,0], [c.real, c.imag])