https://git.ruby-lang.org/ruby.git/commit/?id=e07d450dea

From e07d450deae500422b7693a30c75c5b1567601a2 Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@r...>
Date: Mon, 8 Aug 2022 22:43:56 +0900
Subject: [ruby/date] Fix Time#to_datetime before calendar reform

Time is always in the proleptic Gregorian calendar.
Also DateTime#to_time should convert to the Gregorian calendar first,
before extracting its components.

https://bugs.ruby-lang.org/issues/18946#change-98527

https://github.com/ruby/date/commit/b2aee75248
---
 ext/date/date_core.c        | 13 +++++++++----
 test/date/test_date_conv.rb | 17 +++++++++++++++++
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/ext/date/date_core.c b/ext/date/date_core.c
index 1c0d1c4920..c68f70e5f8 100644
--- a/ext/date/date_core.c
+++ b/ext/date/date_core.c
@@ -8811,7 +8811,7 @@ time_to_datetime(VALUE self) https://github.com/ruby/ruby/blob/trunk/ext/date/date_core.c#L8811
     ret = d_complex_new_internal(cDateTime,
 				 nth, 0,
 				 0, sf,
-				 of, DEFAULT_SG,
+				 of, GREGORIAN,
 				 ry, m, d,
 				 h, min, s,
 				 HAVE_CIVIL | HAVE_TIME);
@@ -8915,12 +8915,17 @@ date_to_datetime(VALUE self) https://github.com/ruby/ruby/blob/trunk/ext/date/date_core.c#L8915
 static VALUE
 datetime_to_time(VALUE self)
 {
-    volatile VALUE dup = dup_obj(self);
+    get_d1(self);
+
+    if (m_julian_p(dat)) {
+	self = d_lite_gregorian(self);
+	get_d1a(self);
+	dat = adat;
+    }
+
     {
 	VALUE t;
 
-	get_d1(dup);
-
 	t = rb_funcall(rb_cTime,
 		   rb_intern("new"),
                    7,
diff --git a/test/date/test_date_conv.rb b/test/date/test_date_conv.rb
index d41ff45d85..ed478b41bb 100644
--- a/test/date/test_date_conv.rb
+++ b/test/date/test_date_conv.rb
@@ -77,6 +77,11 @@ class TestDateConv < Test::Unit::TestCase https://github.com/ruby/ruby/blob/trunk/test/date/test_date_conv.rb#L77
     assert_equal([2004, 9, 19, 1, 2, 3, 456789],
 		 [t.year, t.mon, t.mday, t.hour, t.min, t.sec, t.usec])
 
+    d = DateTime.new(1582, 10, 3, 1, 2, 3, 0) + 456789.to_r/86400000000
+    t = d.to_time.utc
+    assert_equal([1582, 10, 13, 1, 2, 3, 456789],
+		 [t.year, t.mon, t.mday, t.hour, t.min, t.sec, t.usec])
+
     if Time.allocate.respond_to?(:nsec)
       d = DateTime.new(2004, 9, 19, 1, 2, 3, 0) + 456789123.to_r/86400000000000
       t = d.to_time.utc
@@ -100,6 +105,10 @@ class TestDateConv < Test::Unit::TestCase https://github.com/ruby/ruby/blob/trunk/test/date/test_date_conv.rb#L105
     t = Time.utc(2004, 9, 19, 1, 2, 3, 456789)
     d = t.to_date
     assert_equal([2004, 9, 19, 0], [d.year, d.mon, d.mday, d.day_fraction])
+
+    t = Time.utc(1582, 10, 13, 1, 2, 3, 456789)
+    d = t.to_date # using ITALY
+    assert_equal([1582, 10, 3, 0], [d.year, d.mon, d.mday, d.day_fraction])
   end
 
   def test_to_date__from_date
@@ -136,6 +145,14 @@ class TestDateConv < Test::Unit::TestCase https://github.com/ruby/ruby/blob/trunk/test/date/test_date_conv.rb#L145
 		 [d.year, d.mon, d.mday, d.hour, d.min, d.sec,
 		  d.sec_fraction, d.offset])
 
+    t = Time.utc(1582, 10, 13, 1, 2, 3, 456789)
+    d = t.to_datetime # using ITALY
+    assert_equal([1582, 10, 3, 1, 2, 3,
+		  456789.to_r/1000000,
+		  0],
+		 [d.year, d.mon, d.mday, d.hour, d.min, d.sec,
+		  d.sec_fraction, d.offset])
+
     t = Time.now
     d = t.to_datetime
     require 'time'
-- 
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