Bug 1838173: Allow to set the Gregorian change date for ISO-8601 calendars. r=platform-i18n-reviewers,dminor

Add a patch to work around <https://unicode-org.atlassian.net/jira/software/c/projects/ICU/issues/ICU-22412>.

Differential Revision: https://phabricator.services.mozilla.com/D180796

intl/components/gtest/TestDateTimeFormat.cpp

@@ -564,4 +564,58 @@ TEST(IntlDateTimeFormat, TryFormatToParts)
 
   ASSERT_EQ(parts.length(), 9u);
 }
+
+TEST(IntlDateTimeFormat, SetStartTimeIfGregorian)
+{
+  DateTimeFormat::StyleBag style{};
+  style.date = Some(DateTimeFormat::Style::Long);
+
+  auto timeZone = Some(MakeStringSpan(u"UTC"));
+
+  // Beginning of ECMAScript time.
+  constexpr double StartOfTime = -8.64e15;
+
+  // Gregorian change date defaults to October 15, 1582 in ICU. Test with a date
+  // before the default change date, in this case January 1, 1582.
+  constexpr double FirstJanuary1582 = -12244089600000.0;
+
+  // One year expressed in milliseconds.
+  constexpr double oneYear = (365 * 24 * 60 * 60) * 1000.0;
+
+  // Test with and without explicit calendar. The start time of the calendar can
+  // only be adjusted for the Gregorian and the ISO-8601 calendar.
+  for (const char* locale : {
+           "en-US",
+           "en-US-u-ca-gregory",
+           "en-US-u-ca-iso8601",
+       }) {
+    auto gen = DateTimePatternGenerator::TryCreate(locale).unwrap();
+
+    auto dtFormat = DateTimeFormat::TryCreateFromStyle(
+                        MakeStringSpan(locale), style, gen.get(), timeZone)
+                        .unwrap();
+
+    TestBuffer<char> buffer;
+
+    // Before the default Gregorian change date, so interpreted in the Julian
+    // calendar, which is December 22, 1581.
+    dtFormat->TryFormat(FirstJanuary1582, buffer).unwrap();
+    ASSERT_TRUE(buffer.verboseMatches("December 22, 1581"));
+
+    // After default Gregorian change date, so January 1, 1583.
+    dtFormat->TryFormat(FirstJanuary1582 + oneYear, buffer).unwrap();
+    ASSERT_TRUE(buffer.verboseMatches("January 1, 1583"));
+
+    // Adjust the start time to use a proleptic Gregorian calendar.
+    dtFormat->SetStartTimeIfGregorian(StartOfTime);
+
+    // Now interpreted in proleptic Gregorian calendar at January 1, 1582.
+    dtFormat->TryFormat(FirstJanuary1582, buffer).unwrap();
+    ASSERT_TRUE(buffer.verboseMatches("January 1, 1582"));
+
+    // Still January 1, 1583.
+    dtFormat->TryFormat(FirstJanuary1582 + oneYear, buffer).unwrap();
+    ASSERT_TRUE(buffer.verboseMatches("January 1, 1583"));
+  }
+}
 }  // namespace mozilla::intl

intl/icu-patches/bug-1838173-ICU-22412-start-time-iso8601.diff

@@ -0,0 +1,47 @@
+# Allow to set the Gregorian change date for ISO8601 calendars.
+#
+# ICU bug: https://unicode-org.atlassian.net/browse/ICU-22412
+
+diff --git a/intl/icu/source/i18n/ucal.cpp b/intl/icu/source/i18n/ucal.cpp
+--- a/intl/icu/source/i18n/ucal.cpp
++++ b/intl/icu/source/i18n/ucal.cpp
+@@ -22,10 +22,11 @@
+ #include "unicode/ustring.h"
+ #include "unicode/strenum.h"
+ #include "unicode/localpointer.h"
+ #include "cmemory.h"
+ #include "cstring.h"
++#include "iso8601cal.h"
+ #include "ustrenum.h"
+ #include "uenumimp.h"
+ #include "ulist.h"
+ #include "ulocimp.h"
+ 
+@@ -305,11 +306,12 @@ ucal_setGregorianChange(UCalendar *cal, 
+         // We normally don't check "this" pointers for nullptr, but this here avoids
+         // compiler-generated exception-throwing code in case cal == nullptr.
+         *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+         return;
+     }
+-    if(typeid(*cpp_cal) != typeid(GregorianCalendar)) {
++    if(typeid(*cpp_cal) != typeid(GregorianCalendar) &&
++       typeid(*cpp_cal) != typeid(ISO8601Calendar)) {
+         *pErrorCode = U_UNSUPPORTED_ERROR;
+         return;
+     }
+     gregocal->setGregorianChange(date, *pErrorCode);
+ }
+@@ -327,11 +329,12 @@ ucal_getGregorianChange(const UCalendar 
+         // We normally don't check "this" pointers for nullptr, but this here avoids
+         // compiler-generated exception-throwing code in case cal == nullptr.
+         *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+         return (UDate)0;
+     }
+-    if(typeid(*cpp_cal) != typeid(GregorianCalendar)) {
++    if(typeid(*cpp_cal) != typeid(GregorianCalendar) &&
++       typeid(*cpp_cal) != typeid(ISO8601Calendar)) {
+         *pErrorCode = U_UNSUPPORTED_ERROR;
+         return (UDate)0;
+     }
+     return gregocal->getGregorianChange();
+ }

intl/icu/source/i18n/ucal.cpp

@@ -24,6 +24,7 @@
 #include "unicode/localpointer.h"
 #include "cmemory.h"
 #include "cstring.h"
+#include "iso8601cal.h"
 #include "ustrenum.h"
 #include "uenumimp.h"
 #include "ulist.h"
@@ -307,7 +308,8 @@ ucal_setGregorianChange(UCalendar *cal, UDate date, UErrorCode *pErrorCode) {
         *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
         return;
     }
-    if(typeid(*cpp_cal) != typeid(GregorianCalendar)) {
+    if(typeid(*cpp_cal) != typeid(GregorianCalendar) &&
+       typeid(*cpp_cal) != typeid(ISO8601Calendar)) {
         *pErrorCode = U_UNSUPPORTED_ERROR;
         return;
     }
@@ -329,7 +331,8 @@ ucal_getGregorianChange(const UCalendar *cal, UErrorCode *pErrorCode) {
         *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
         return (UDate)0;
     }
-    if(typeid(*cpp_cal) != typeid(GregorianCalendar)) {
+    if(typeid(*cpp_cal) != typeid(GregorianCalendar) &&
+       typeid(*cpp_cal) != typeid(ISO8601Calendar)) {
         *pErrorCode = U_UNSUPPORTED_ERROR;
         return (UDate)0;
     }

intl/update-icu.sh

@@ -58,6 +58,7 @@ for patch in \
  bug-1636984-append-item-dayperiod-fractional-seconds.diff \
  bug-1706949-wasi-workaround.diff \
  bug-1790071-ICU-22132-standardize-vtzone-output.diff \
+ bug-1838173-ICU-22412-start-time-iso8601.diff \
 ; do
   echo "Applying local patch $patch"
   patch -d ${icu_dir}/../../ -p1 --no-backup-if-mismatch < ${icu_dir}/../icu-patches/$patch