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ICU-23277 Update Coptic calendar to use single era #4081

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9d7e611
ICU-23277 Update Coptic calendar to use single era
FrankYFTang Jul 15, 2026
120895e
ICU-23277 Update C++ test cases for single-era Coptic calendar
FrankYFTang Jul 15, 2026
19ef409
ICU-23277 Remove Coptic from IBMCalendarTest era 0 test list
FrankYFTang Jul 15, 2026
f685298
ICU-23277 Fix Java code formatting in CopticTest
FrankYFTang Jul 15, 2026
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27 changes: 12 additions & 15 deletions icu4c/source/i18n/coptccal.cpp
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Expand Up @@ -66,16 +66,8 @@ CopticCalendar::handleGetExtendedYear(UErrorCode& status)
if (newerField(UCAL_EXTENDED_YEAR, UCAL_YEAR) == UCAL_EXTENDED_YEAR) {
return internalGet(UCAL_EXTENDED_YEAR, 1); // Default to year 1
}
// The year defaults to the epoch start, the era to CE
int32_t era = internalGet(UCAL_ERA, CE);

@sffc sffc Jul 15, 2026

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Issue: I think if someone explicitly set the era to the old backwards-counting era Before Diocletian (BD), then we should still do 1 - X. We should just never create BD dates implicitly.

@FrankYFTang FrankYFTang Jul 15, 2026

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are you suggesting we do not change this part?

@sffc sffc Jul 15, 2026

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I'm suggesting that as long as the Before Diocletian era is public and stable, we should probably continue respecting it on input.

@sffc sffc Jul 15, 2026

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I'm suggesting that as long as the Before Diocletian era is public and stable, we should probably continue respecting it on input.

@FrankYFTang FrankYFTang Jul 16, 2026

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none of them are public. They are all private

if (era == BCE) {
return 1 - internalGet(UCAL_YEAR, 1); // Convert to extended year
}
if (era == CE){
return internalGet(UCAL_YEAR, 1); // Default to year 1
}
status = U_ILLEGAL_ARGUMENT_ERROR;
return 0;
// Default to year 1
return internalGet(UCAL_YEAR, 1);
}

IMPL_SYSTEM_DEFAULT_CENTURY(CopticCalendar, "@calendar=coptic")
Expand All @@ -86,16 +78,21 @@ CopticCalendar::getJDEpochOffset() const
return COPTIC_JD_EPOCH_OFFSET;
}

int32_t CopticCalendar::extendedYearToEra(int32_t extendedYear) const {
return extendedYear <= 0 ? BCE : CE;
int32_t CopticCalendar::extendedYearToEra(int32_t /* extendedYear */) const {
return CE;
}

int32_t CopticCalendar::extendedYearToYear(int32_t extendedYear) const {
return extendedYear <= 0 ? 1 - extendedYear : extendedYear;
return extendedYear;
}

bool CopticCalendar::isEra0CountingBackward() const {
return true;
int32_t
CopticCalendar::handleGetLimit(UCalendarDateFields field, ELimitType limitType) const
{
if (field == UCAL_ERA) {
return CE; // Only one era in this mode, era is always CE
}
return CECalendar::handleGetLimit(field, limitType);
}

int32_t
Expand Down
3 changes: 2 additions & 1 deletion icu4c/source/i18n/coptccal.h
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Expand Up @@ -191,9 +191,10 @@ class CopticCalendar : public CECalendar {
int32_t extendedYearToYear(int32_t extendedYear) const override;

/**
* Calculate the limit for a specified type of limit and field
* @internal
*/
bool isEra0CountingBackward() const override;
virtual int32_t handleGetLimit(UCalendarDateFields field, ELimitType limitType) const override;
public:
/**
* Override Calendar Returns a unique class ID POLYMORPHICALLY. Pure virtual
Expand Down
1 change: 0 additions & 1 deletion icu4c/source/test/cintltst/ccaltst.c
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Expand Up @@ -2145,7 +2145,6 @@ static const EraTestItem eraTestItems[] = {
/* calendars with non-modern era 0 that goes backwards, max era == 1 */
{ "en@calendar=gregorian", true },
{ "en@calendar=roc", true },
{ "en@calendar=coptic", true },
/* calendars with non-modern era 0 that goes forwards, max era > 1 */
{ "en@calendar=japanese", false },
{ "en@calendar=chinese", false },
Expand Down
10 changes: 5 additions & 5 deletions icu4c/source/test/intltest/calcasts.cpp
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Expand Up @@ -399,15 +399,15 @@ void CalendarCaseTest::Coptic() {
{2402708.5, 1, 1582, 8, 10, TUE, 0, 0, 0}, // Gregorian: 17/04/1866
{2402971.5, 1, 1583, 4, 28, SAT, 0, 0, 0}, // Gregorian: 05/01/1867
{2403344.5, 1, 1584, 5, 5, MON, 0, 0, 0}, // Gregorian: 13/01/1868
{1721059.5, 0, 285, 5, 7, SAT, 0, 0, 0}, // Gregorian: 01/01/0000
{1721425.5, 0, 284, 5, 8, MON, 0, 0, 0}, // Gregorian: 01/01/0001
{1824663.5, 0, 2, 13, 6, WED, 0, 0, 0}, // Gregorian: 29/08/0283
{1824664.5, 0, 1, 1, 1, THU, 0, 0, 0}, // Gregorian: 30/08/0283
{1721059.5, 1, -284, 5, 7, SAT, 0, 0, 0}, // Gregorian: 01/01/0000
{1721425.5, 1, -283, 5, 8, MON, 0, 0, 0}, // Gregorian: 01/01/0001
{1824663.5, 1, -1, 13, 6, WED, 0, 0, 0}, // Gregorian: 29/08/0283
{1824664.5, 1, 0, 1, 1, THU, 0, 0, 0}, // Gregorian: 30/08/0283
{1825029.5, 1, 1, 1, 1, FRI, 0, 0, 0}, // Gregorian: 29/08/0284
{1825394.5, 1, 2, 1, 1, SAT, 0, 0, 0}, // Gregorian: 29/08/0285
{1825759.5, 1, 3, 1, 1, SUN, 0, 0, 0}, // Gregorian: 29/08/0286
{1826125.5, 1, 4, 1, 1, TUE, 0, 0, 0}, // Gregorian: 30/08/0287
{1825028.5, 0, 1, 13, 5, THU, 0, 0, 0}, // Gregorian: 28/08/0284
{1825028.5, 1, 0, 13, 5, THU, 0, 0, 0}, // Gregorian: 28/08/0284
{1825393.5, 1, 1, 13, 5, FRI, 0, 0, 0}, // Gregorian: 28/08/0285
{1825758.5, 1, 2, 13, 5, SAT, 0, 0, 0}, // Gregorian: 28/08/0286
{1826123.5, 1, 3, 13, 5, SUN, 0, 0, 0}, // Gregorian: 28/08/0287
Expand Down
24 changes: 24 additions & 0 deletions icu4c/source/test/intltest/caltest.cpp
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Expand Up @@ -214,6 +214,7 @@ void CalendarTest::runIndexedTest( int32_t index, UBool exec, const char* &name,
TESTCASE_AUTO(Test22441Year88369);
TESTCASE_AUTO(Test22730JapaneseOverflow);
TESTCASE_AUTO(Test22730CopticOverflow);
TESTCASE_AUTO(TestBug23277);
TESTCASE_AUTO(Test22962ComputeJulianDayOverflow);

TESTCASE_AUTO(TestAddOverflow);
Expand Down Expand Up @@ -6156,6 +6157,29 @@ void CalendarTest::Test22730CopticOverflow() {
assertEquals("status return without overflow", status, U_ILLEGAL_ARGUMENT_ERROR);
}

void CalendarTest::TestBug23277() {
IcuTestErrorCode status(*this, "TestBug23277");
LocalPointer<Calendar> cal(
Calendar::createInstance(Locale("en-u-ca-coptic"), status),
status);
if (failure(status, "Calendar::createInstance en-u-ca-coptic")) return;

cal->set(2000, 0, 1); // 2000 CE (around 1716 AM)
assertEquals("Era for positive extended year should be CE (1)",
(int32_t)CopticCalendar::CE, cal->get(UCAL_ERA, status));
assertEquals("Minimum era should be CE (1)",
(int32_t)CopticCalendar::CE, cal->getMinimum(UCAL_ERA));
assertEquals("Maximum era should be CE (1)",
(int32_t)CopticCalendar::CE, cal->getMaximum(UCAL_ERA));

cal->clear();
cal->set(UCAL_EXTENDED_YEAR, -283); // Year -283 AM (Julian year 1 CE)
assertEquals("Era for negative extended year should be CE (1) in single-era model",
(int32_t)CopticCalendar::CE, cal->get(UCAL_ERA, status));
assertEquals("Year for negative extended year should equal extended year in single-era model",
-283, cal->get(UCAL_YEAR, status));
}

void CalendarTest::Test22962ComputeJulianDayOverflow() {
UErrorCode status = U_ZERO_ERROR;
LocalPointer<Calendar> calendar(
Expand Down
1 change: 1 addition & 0 deletions icu4c/source/test/intltest/caltest.h
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Expand Up @@ -351,6 +351,7 @@ class CalendarTest: public CalendarTimeZoneTest {
void Test22633RollTwiceGetTimeOverflow();
void Test22730JapaneseOverflow();
void Test22730CopticOverflow();
void TestBug23277();
void Test22962ComputeJulianDayOverflow();
void Test22962MonthAddOneOverflow();

Expand Down
33 changes: 18 additions & 15 deletions icu4j/main/core/src/main/java/com/ibm/icu/util/CopticCalendar.java
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Expand Up @@ -248,12 +248,6 @@ public String getType() {
* @internal
* @deprecated This API is ICU internal only.
*/
@Override
@Deprecated
protected boolean isEra0CountingBackward() {
return true;
}

/**
* {@inheritDoc}
*
Expand All @@ -267,13 +261,7 @@ protected int handleGetExtendedYear() {
if (newerField(EXTENDED_YEAR, YEAR) == EXTENDED_YEAR) {
eyear = internalGet(EXTENDED_YEAR, 1); // Default to year 1
} else {
// The year defaults to the epoch start, the era to AD
int era = internalGet(ERA, CE);
if (era == BCE) {
eyear = 1 - internalGet(YEAR, 1); // Convert to extended year
} else {
eyear = internalGet(YEAR, 1); // Default to year 1
}
eyear = internalGet(YEAR, 1); // Default to year 1
}
return eyear;
}
Expand All @@ -287,7 +275,7 @@ protected int handleGetExtendedYear() {
@Deprecated
@Override
protected int extendedYearToEra(int eyear) {
return (eyear <= 0) ? BCE : CE;
return CE;
}

/**
Expand All @@ -299,7 +287,22 @@ protected int extendedYearToEra(int eyear) {
@Deprecated
@Override
protected int extendedYearToYear(int eyear) {
return (eyear <= 0) ? 1 - eyear : eyear;
return eyear;
}

/**
* {@inheritDoc}
*
* @internal
* @deprecated This API is ICU internal only.
*/
@Override
@Deprecated
protected int handleGetLimit(int field, int limitType) {
if (field == ERA) {
return CE; // Only one era in this mode, era is always CE

@sffc sffc Jul 15, 2026 •
edited
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Issue: Coptic has never used CE (Common Era). This looks like a typo made during some previous refactor, since the era has been sometimes called AD, but that stands for "After Diocletian", not "Anno Domini". The best English/Latin name for this era based on my research is Anno Martyrum or "AM".

Unless CE is intended to stand for "Coptic Era"? 🤔

@FrankYFTang FrankYFTang Jul 15, 2026

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See https://github.com/unicode-org/icu/blame/7ce89a8fbb84b3ef950df9cdc162d3f7249c2e3a/icu4j/main/core/src/main/java/com/ibm/icu/util/CopticCalendar.java#L124
it came from moving
" private static final int CE_AD = 1; " in CECalendar.java

@FrankYFTang FrankYFTang Jul 15, 2026

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It is used in the code

icu/icu4j/main/core/src/main/java/com/ibm/icu/util/CopticCalendar.java

Line 271 in 7ce89a8

int era = internalGet(ERA, CE);
look at the code removed above

@sffc sffc Jul 15, 2026

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ok so the CE era means "Coptic/Ethiopian"? 🤔

@FrankYFTang FrankYFTang Jul 16, 2026

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@yumaoka You need to ask him.

@yumaoka yumaoka Oct 22, 2026

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The original implementation was merged into ICU4J. Doug Felt created the initial version. I guess he got the implementation from someone else. I did C port about two decades ago. I think "CE" era means "Copting/Ethiopian".

}
return super.handleGetLimit(field, limitType);
}

/**
Expand Down
33 changes: 25 additions & 8 deletions icu4j/main/core/src/test/java/com/ibm/icu/dev/test/calendar/CopticTest.java
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Expand Up @@ -107,15 +107,15 @@ public void TestCases() {
new TestCase(2402708.5, 1, 1582, 8, 10, TUE, 0, 0, 0), // Gregorian: 17/04/1866
new TestCase(2402971.5, 1, 1583, 4, 28, SAT, 0, 0, 0), // Gregorian: 05/01/1867
new TestCase(2403344.5, 1, 1584, 5, 5, MON, 0, 0, 0), // Gregorian: 13/01/1868
new TestCase(1721059.5, 0, 285, 5, 7, SAT, 0, 0, 0), // Gregorian: 01/01/0000
new TestCase(1721425.5, 0, 284, 5, 8, MON, 0, 0, 0), // Gregorian: 01/01/0001
new TestCase(1824663.5, 0, 2, 13, 6, WED, 0, 0, 0), // Gregorian: 29/08/0283
new TestCase(1824664.5, 0, 1, 1, 1, THU, 0, 0, 0), // Gregorian: 30/08/0283
new TestCase(1721059.5, 1, -284, 5, 7, SAT, 0, 0, 0), // Gregorian: 01/01/0000
new TestCase(1721425.5, 1, -283, 5, 8, MON, 0, 0, 0), // Gregorian: 01/01/0001
new TestCase(1824663.5, 1, -1, 13, 6, WED, 0, 0, 0), // Gregorian: 29/08/0283
new TestCase(1824664.5, 1, 0, 1, 1, THU, 0, 0, 0), // Gregorian: 30/08/0283
new TestCase(1825029.5, 1, 1, 1, 1, FRI, 0, 0, 0), // Gregorian: 29/08/0284
new TestCase(1825394.5, 1, 2, 1, 1, SAT, 0, 0, 0), // Gregorian: 29/08/0285
new TestCase(1825759.5, 1, 3, 1, 1, SUN, 0, 0, 0), // Gregorian: 29/08/0286
new TestCase(1826125.5, 1, 4, 1, 1, TUE, 0, 0, 0), // Gregorian: 30/08/0287
new TestCase(1825028.5, 0, 1, 13, 5, THU, 0, 0, 0), // Gregorian: 28/08/0284
new TestCase(1825028.5, 1, 0, 13, 5, THU, 0, 0, 0), // Gregorian: 28/08/0284
new TestCase(1825393.5, 1, 1, 13, 5, FRI, 0, 0, 0), // Gregorian: 28/08/0285
new TestCase(1825758.5, 1, 2, 13, 5, SAT, 0, 0, 0), // Gregorian: 28/08/0286
new TestCase(1826123.5, 1, 3, 13, 5, SUN, 0, 0, 0), // Gregorian: 28/08/0287
Expand Down Expand Up @@ -183,9 +183,8 @@ public void TestEraStart() {
assertEquals("Coptic Date", "Fri Jan 01, 0001 AD", copticFmt.format(cal));
assertEquals("Gregorian Date", "Fri Aug 29, 0284 AD", fmt.format(cal.getTime()));

cal.set(Calendar.ERA, 0);
cal.set(Calendar.YEAR, 1);
assertEquals("Coptic Date", "Thu Jan 01, 0001 BC", copticFmt.format(cal));
cal.set(Calendar.EXTENDED_YEAR, 0);
assertEquals("Coptic Date", "Thu Jan 01, 0000 AD", copticFmt.format(cal));
assertEquals("Gregorian Date", "Thu Aug 30, 0283 AD", fmt.format(cal.getTime()));
}

Expand Down Expand Up @@ -458,4 +457,22 @@ public int getEndDay() {
}
}
}

@Test
public void TestBug23277() {
CopticCalendar cal = new CopticCalendar(ULocale.forLanguageTag("en-u-ca-coptic"));
assertEquals("Minimum era should be CE (1)", 1, cal.getMinimum(Calendar.ERA));
assertEquals("Maximum era should be CE (1)", 1, cal.getMaximum(Calendar.ERA));

cal.set(Calendar.EXTENDED_YEAR, 1716);
assertEquals("Era for positive extended year should be CE (1)", 1, cal.get(Calendar.ERA));
assertEquals("Year should be 1716", 1716, cal.get(Calendar.YEAR));

cal.set(Calendar.EXTENDED_YEAR, -283);
assertEquals("Era for negative extended year should be CE (1)", 1, cal.get(Calendar.ERA));
assertEquals(
"Year for negative extended year should equal extended year",
-283,
cal.get(Calendar.YEAR));
}
}
1 change: 0 additions & 1 deletion icu4j/main/core/src/test/java/com/ibm/icu/dev/test/calendar/IBMCalendarTest.java
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Expand Up @@ -2463,7 +2463,6 @@ public void TestAddRollEra0AndEraBounds() {
// calendars with non-modern era 0 that goes backwards, max era == 1
"en@calendar=gregorian",
"en@calendar=roc",
"en@calendar=coptic",
// calendars with non-modern era 0 that goes backwards, max era > 1
"en@calendar=japanese",
// calendars with non-modern era 0 that goes forwards, max era > 1
Expand Down
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