Change Temporal.Calendar compare semantics to use .id

Compare semantics for custom calendars that _don't_ extend
Temporal.Calendar (and therefore don't have the internal slot) use the
value of the .id property, instead of calling toString().

Normative PR: https://github.com/tc39/proposal-temporal/pull/2482

harness/temporalHelpers.js

@@ -1520,7 +1520,8 @@ var TemporalHelpers = {
         // Remove the HasProperty check resulting from the above constructor call
         assert.sameValue(calls.pop(), `has ${objectName}.calendar`);
         return result;
-      }
+      },
+      id: "iso8601",
     };
     // Automatically generate the other methods that don't need any custom code
     ["toString", "dateUntil", "era", "eraYear", "year", "month", "monthCode", "day", "daysInMonth", "fields", "mergeFields"].forEach((methodName) => {

test/built-ins/Temporal/PlainDate/prototype/equals/argument-object-valid.js

@@ -11,6 +11,6 @@ const instance = new Temporal.PlainDate(2000, 5, 2);
 assert.sameValue(instance.equals({ year: 2000, month: 5, day: 2 }), true, "same date");
 assert.sameValue(instance.equals({ year: 2000, month: 5, day: 4 }), false, "different date");
 
-const calendar = { toString() { return "a" } };
+const calendar = { id: "a" };
 assert.sameValue(instance.withCalendar(calendar).equals({ year: 2000, month: 5, day: 2 }),
   false, "different calendar");

test/built-ins/Temporal/PlainDate/prototype/equals/argument-string.js

@@ -11,5 +11,5 @@ const instance = new Temporal.PlainDate(2000, 5, 2);
 assert.sameValue(instance.equals("2000-05-02"), true, "same date");
 assert.sameValue(instance.equals("2000-05-04"), false, "different date");
 
-const calendar = { toString() { return "a" } };
+const calendar = { id: "a" };
 assert.sameValue(instance.withCalendar(calendar).equals("2000-05-02"), false, "different calendar");

test/built-ins/Temporal/PlainDate/prototype/equals/calendar-call-different.js

@@ -4,27 +4,31 @@
 /*---
 esid: sec-temporal.plaindate.protoype.equals
 description: test if the calendar is compared
+includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
-class CalendarTraceToString extends Temporal.Calendar {
+class CalendarTraceId extends Temporal.Calendar {
   constructor(id) {
     super("iso8601");
     this.id_ = id;
     this.calls = 0;
   }
-  toString() {
+  get id() {
     ++this.calls;
     return this.id_;
   }
+  toString() {
+    TemporalHelpers.assertUnreachable('toString should not be called');
+  }
 };
 
-const calendar1 = new CalendarTraceToString("a");
+const calendar1 = new CalendarTraceId("a");
 const date1 = new Temporal.PlainDate(1914, 2, 23, calendar1);
 
-const calendar2 = new CalendarTraceToString("b");
+const calendar2 = new CalendarTraceId("b");
 const date2 = new Temporal.PlainDate(1914, 2, 23, calendar2);
 
 assert.sameValue(date1.equals(date2), false, "different calendars");
-assert.sameValue(calendar1.calls, 1, "calendar1 toString() calls");
+assert.sameValue(calendar1.calls, 1, "calendar1 id getter calls");
-assert.sameValue(calendar2.calls, 1, "calendar2 toString() calls");
+assert.sameValue(calendar2.calls, 1, "calendar2 id getter calls");

test/built-ins/Temporal/PlainDate/prototype/equals/calendar-call-same.js

@@ -4,6 +4,7 @@
 /*---
 esid: sec-temporal.plaindate.protoype.equals
 description: test if the calendar is compared
+includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
@@ -13,10 +14,13 @@ class CalendarTraceToString extends Temporal.Calendar {
     this.id_ = id;
     this.calls = 0;
   }
-  toString() {
+  get id() {
     ++this.calls;
     return this.id_;
   }
+  toString() {
+    TemporalHelpers.assertUnreachable('toString should not be called');
+  }
 };
 
 const calendar1 = new CalendarTraceToString("a");
@@ -26,5 +30,5 @@ const calendar2 = new CalendarTraceToString("a");
 const date2 = new Temporal.PlainDate(1914, 2, 23, calendar2);
 
 assert.sameValue(date1.equals(date2), true, "same calendar id");
-assert.sameValue(calendar1.calls, 1, "calendar1 toString() calls");
+assert.sameValue(calendar1.calls, 1, "calendar1 id getter calls");
-assert.sameValue(calendar2.calls, 1, "calendar2 toString() calls");
+assert.sameValue(calendar2.calls, 1, "calendar2 id getter calls");

test/built-ins/Temporal/PlainDate/prototype/since/calendar-mismatch.js

@@ -3,12 +3,12 @@
 
 /*---
 esid: sec-temporal.plaindate.prototype.since
-description: RangeError thrown if calendars' toString results do not match
+description: RangeError thrown if calendars' id properties do not match
 features: [Temporal]
 ---*/
 
-const calendar1 = { toString() { return "A"; } };
+const calendar1 = { id: "A" };
-const calendar2 = { toString() { return "B"; } };
+const calendar2 = { id: "B" };
 
 const plainDate1 = new Temporal.PlainDate(2000, 1, 1, calendar1);
 const plainDate2 = new Temporal.PlainDate(2000, 1, 1, calendar2);

test/built-ins/Temporal/PlainDate/prototype/since/order-of-operations.js

@@ -29,12 +29,8 @@ const expected = [
   "get other.calendar.dateFromFields",
   "call other.calendar.dateFromFields",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/built-ins/Temporal/PlainDate/prototype/toString/calendar-tostring.js

@@ -4,14 +4,18 @@
 /*---
 esid: sec-temporal.plaindate.protoype.tostring
 description: Number of observable 'toString' calls on the calendar for each value of calendarName
+includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
 let calls;
 const customCalendar = {
-  toString() {
+  get id() {
     ++calls;
     return "custom";
+  },
+  toString() {
+    TemporalHelpers.assertUnreachable('toString should not be called');
   }
 };
 const date = new Temporal.PlainDate(2000, 5, 2, customCalendar);
@@ -24,6 +28,6 @@ const date = new Temporal.PlainDate(2000, 5, 2, customCalendar);
 ].forEach(([calendarName, expectedResult, expectedCalls]) => {
   calls = 0;
   const result = date.toString({ calendarName });
-  assert.sameValue(result, expectedResult, `toString output for calendarName = ${calendarName}`);
+  assert.sameValue(result, expectedResult, `id for calendarName = ${calendarName}`);
-  assert.sameValue(calls, expectedCalls, `calls to toString for calendarName = ${calendarName}`);
+  assert.sameValue(calls, expectedCalls, `calls to id getter for calendarName = ${calendarName}`);
 });

test/built-ins/Temporal/PlainDate/prototype/toString/calendarname-always.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05-02[u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-02[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-02[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05-02[u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05-02[u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-02[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-02[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-02[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-02[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDate/prototype/toString/calendarname-auto.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05-02", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-02[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-02[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05-02", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05-02", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-02[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-02[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-02[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-02[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDate/prototype/toString/calendarname-critical.js

@@ -11,10 +11,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05-02[!u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-02[!u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-02[!u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05-02[!u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05-02[!u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-02[!u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-02[!u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-02[!u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-02[!u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDate/prototype/toString/calendarname-never.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05-02", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-02", "custom"],
+  [[{ id: "custom" }], "2000-05-02", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05-02", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05-02", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-02", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-02", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-02", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-02", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDate/prototype/toString/calendarname-undefined.js

@@ -16,10 +16,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05-02", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-02[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-02[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05-02", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05-02", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-02[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-02[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-02[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-02[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDate/prototype/toString/calendarname-wrong-type.js

@@ -16,7 +16,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const date = new Temporal.PlainDate(2000, 5, 2, calendar);
 

test/built-ins/Temporal/PlainDate/prototype/toString/options-undefined.js

@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const date1 = new Temporal.PlainDate(2000, 5, 2);
 const date2 = new Temporal.PlainDate(2000, 5, 2, calendar);

test/built-ins/Temporal/PlainDate/prototype/toString/order-of-operations.js

@@ -12,9 +12,7 @@ const expected = [
   "get options.calendarName",
   "get options.calendarName.toString",
   "call options.calendarName.toString",
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
-  "call this.calendar.toString",
 ];
 const actual = [];
 

test/built-ins/Temporal/PlainDate/prototype/until/calendar-mismatch.js

@@ -3,12 +3,12 @@
 
 /*---
 esid: sec-temporal.plaindate.prototype.until
-description: RangeError thrown if calendars' toString results do not match
+description: RangeError thrown if calendars' id properties do not match
 features: [Temporal]
 ---*/
 
-const calendar1 = { toString() { return "A"; } };
+const calendar1 = { id: "A" };
-const calendar2 = { toString() { return "B"; } };
+const calendar2 = { id: "B" };
 
 const plainDate1 = new Temporal.PlainDate(2000, 1, 1, calendar1);
 const plainDate2 = new Temporal.PlainDate(2000, 1, 1, calendar2);

test/built-ins/Temporal/PlainDate/prototype/until/order-of-operations.js

@@ -29,12 +29,8 @@ const expected = [
   "get other.calendar.dateFromFields",
   "call other.calendar.dateFromFields",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/built-ins/Temporal/PlainDateTime/prototype/equals/calendar-checked.js

@@ -9,26 +9,38 @@ features: [Temporal]
 ---*/
 
 const actual = [];
-const calendar1 = TemporalHelpers.toPrimitiveObserver(actual, "A", "calendar1");
+
-const calendar2 = TemporalHelpers.toPrimitiveObserver(actual, "A", "calendar2");
+function makeCalendar(id, objectName) {
-const calendar3 = TemporalHelpers.toPrimitiveObserver(actual, "B", "calendar3");
+  const calendar = {};
+  TemporalHelpers.observeProperty(actual, calendar, "id", id, objectName);
+  return calendar;
+}
+
+const calendar1 = makeCalendar("A", "calendar1");
+const calendar2 = makeCalendar("A", "calendar2");
+const calendar3 = makeCalendar("B", "calendar3");
 const dt1 = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, calendar1);
 const dt1b = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, calendar1);
 const dt2 = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, calendar2);
 const dt3 = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, calendar3);
+actual.splice(0);  // disregard the HasProperty checks done in the constructor
 
 assert.sameValue(dt1.equals(dt1b), true, "same calendar object");
 assert.compareArray(actual, []);
 
 assert.sameValue(dt1.equals(dt2), true, "same calendar string");
-assert.compareArray(actual, ["get calendar1.toString", "call calendar1.toString", "get calendar2.toString", "call calendar2.toString"]);
+assert.compareArray(actual, ["get calendar1.id", "get calendar2.id"]);
 
 actual.splice(0);  // empty it for the next check
 assert.sameValue(dt1.equals(dt3), false, "different calendar string");
-assert.compareArray(actual, ["get calendar1.toString", "call calendar1.toString", "get calendar3.toString", "call calendar3.toString"]);
+assert.compareArray(actual, ["get calendar1.id", "get calendar3.id"]);
 
-const calendar4 = { toString() { throw new Test262Error("should not call calendar4.toString") } };
+const calendar4 = {
-const calendar5 = { toString() { throw new Test262Error("should not call calendar5.toString") } };
+  get id() { TemporalHelpers.assertUnreachable('should not get calendar4.id'); },
+};
+const calendar5 = {
+  get id() { TemporalHelpers.assertUnreachable('should not get calendar5.id'); },
+};
 const dt4 = new Temporal.PlainDateTime(1976, 11, 18, 15, 23, 30, 123, 456, 789, calendar4);
 const dt5 = new Temporal.PlainDateTime(2019, 10, 29, 10, 46, 38, 271, 986, 102, calendar4);
 const dt6 = new Temporal.PlainDateTime(2019, 10, 29, 10, 46, 38, 271, 986, 102, calendar5);

test/built-ins/Temporal/PlainDateTime/prototype/since/different-calendars-throws.js

@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 const dt1 = new Temporal.PlainDateTime(2000, 1, 1, 0, 0, 0, 0, 0, 0);
-const dt2 = new Temporal.PlainDateTime(2000, 1, 1, 0, 0, 0, 0, 0, 0, {});
+const dt2 = new Temporal.PlainDateTime(2000, 1, 1, 0, 0, 0, 0, 0, 0, { id: "custom" });
 
 assert.throws(
   RangeError,

test/built-ins/Temporal/PlainDateTime/prototype/since/order-of-operations.js

@@ -47,12 +47,8 @@ const expected = [
   "get other.calendar.dateFromFields",
   "call other.calendar.dateFromFields",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/built-ins/Temporal/PlainDateTime/prototype/toString/calendar-tostring.js

@@ -4,14 +4,18 @@
 /*---
 esid: sec-temporal.plaindatetime.protoype.tostring
 description: Number of observable 'toString' calls on the calendar for each value of calendarName
+includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
 let calls;
 const customCalendar = {
-  toString() {
+  get id() {
     ++calls;
     return "custom";
+  },
+  toString() {
+    TemporalHelpers.assertUnreachable('toString should not be called');
   }
 };
 const date = new Temporal.PlainDateTime(2000, 5, 2, 12, 34, 56, 987, 654, 321, customCalendar);
@@ -24,6 +28,6 @@ const date = new Temporal.PlainDateTime(2000, 5, 2, 12, 34, 56, 987, 654, 321, c
 ].forEach(([calendarName, expectedResult, expectedCalls]) => {
   calls = 0;
   const result = date.toString({ calendarName });
-  assert.sameValue(result, expectedResult, `toString output for calendarName = ${calendarName}`);
+  assert.sameValue(result, expectedResult, `id for calendarName = ${calendarName}`);
-  assert.sameValue(calls, expectedCalls, `calls to toString for calendarName = ${calendarName}`);
+  assert.sameValue(calls, expectedCalls, `calls to id getter for calendarName = ${calendarName}`);
 });

test/built-ins/Temporal/PlainDateTime/prototype/toString/calendarname-always.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1976-11-18T15:23:00[u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1976-11-18T15:23:00[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1976-11-18T15:23:00[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1976-11-18T15:23:00[u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1976-11-18T15:23:00[u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1976-11-18T15:23:00[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1976-11-18T15:23:00[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1976-11-18T15:23:00[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1976-11-18T15:23:00[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDateTime/prototype/toString/calendarname-auto.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1976-11-18T15:23:00", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1976-11-18T15:23:00[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1976-11-18T15:23:00[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1976-11-18T15:23:00", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1976-11-18T15:23:00", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1976-11-18T15:23:00[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1976-11-18T15:23:00[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1976-11-18T15:23:00[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1976-11-18T15:23:00[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDateTime/prototype/toString/calendarname-critical.js

@@ -11,10 +11,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1976-11-18T15:23:00[!u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1976-11-18T15:23:00[!u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1976-11-18T15:23:00[!u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1976-11-18T15:23:00[!u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1976-11-18T15:23:00[!u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1976-11-18T15:23:00[!u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1976-11-18T15:23:00[!u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1976-11-18T15:23:00[!u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1976-11-18T15:23:00[!u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDateTime/prototype/toString/calendarname-never.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1976-11-18T15:23:00", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1976-11-18T15:23:00", "custom"],
+  [[{ id: "custom" }], "1976-11-18T15:23:00", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1976-11-18T15:23:00", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1976-11-18T15:23:00", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1976-11-18T15:23:00", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1976-11-18T15:23:00", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1976-11-18T15:23:00", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1976-11-18T15:23:00", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDateTime/prototype/toString/calendarname-undefined.js

@@ -16,10 +16,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1976-11-18T15:23:00", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1976-11-18T15:23:00[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1976-11-18T15:23:00[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1976-11-18T15:23:00", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1976-11-18T15:23:00", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1976-11-18T15:23:00[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1976-11-18T15:23:00[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1976-11-18T15:23:00[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1976-11-18T15:23:00[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainDateTime/prototype/toString/calendarname-wrong-type.js

@@ -16,7 +16,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const datetime = new Temporal.PlainDateTime(2000, 5, 2, 12, 34, 56, 987, 654, 321, calendar);
 

test/built-ins/Temporal/PlainDateTime/prototype/toString/options-undefined.js

@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const datetime1 = new Temporal.PlainDateTime(2000, 5, 2, 12, 34, 56, 987, 650, 0);
 const datetime2 = new Temporal.PlainDateTime(2000, 5, 2, 12, 34, 56, 987, 650, 0, calendar);

test/built-ins/Temporal/PlainDateTime/prototype/toString/order-of-operations.js

@@ -21,9 +21,7 @@ const expected = [
   "get options.smallestUnit",
   "get options.smallestUnit.toString",
   "call options.smallestUnit.toString",
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
-  "call this.calendar.toString",
 ];
 const actual = [];
 
@@ -55,9 +53,7 @@ const expectedForFractionalSecondDigits = [
   "get options.roundingMode.toString",
   "call options.roundingMode.toString",
   "get options.smallestUnit",
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
-  "call this.calendar.toString",
 ];
 
 instance.toString(

test/built-ins/Temporal/PlainDateTime/prototype/until/different-calendars-throws.js

@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 const dt1 = new Temporal.PlainDateTime(2000, 1, 1, 0, 0, 0, 0, 0, 0);
-const dt2 = new Temporal.PlainDateTime(2000, 1, 1, 0, 0, 0, 0, 0, 0, {});
+const dt2 = new Temporal.PlainDateTime(2000, 1, 1, 0, 0, 0, 0, 0, 0, { id: "custom" });
 
 assert.throws(
   RangeError,

test/built-ins/Temporal/PlainDateTime/prototype/until/order-of-operations.js

@@ -47,12 +47,8 @@ const expected = [
   "get other.calendar.dateFromFields",
   "call other.calendar.dateFromFields",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/built-ins/Temporal/PlainDateTime/prototype/withPlainDate/argument-plaindate-calendar-same-id.js

@@ -9,13 +9,14 @@ includes: [temporalHelpers.js]
 ---*/
 
 const cal1 = {
-  toString() { return "this is a string"; },
+  id: "this is a string",
+  toString() { return "this is another string"; }
 };
 const cal2 = {
-  id: 'thisisnotiso',
+  id: "this is a string",
   era() { return undefined; },
   eraYear() { return undefined; },
-  toString() { return "this is a string"; },
+  toString() { return "thisisnotiso"; },
   year() { return 2008; },
   month() { return 9; },
   monthCode() { return "M09"; },

test/built-ins/Temporal/PlainMonthDay/prototype/equals/calendars.js

@@ -9,19 +9,20 @@ features: [Temporal]
 ---*/
 
 const expected = [
-  "get calendar a.toString",
+  "get calendar a.id",
-  "call calendar a.toString",
+  "get calendar b.id",
-  "get calendar b.toString",
-  "call calendar b.toString",
 ];
 const actual = [];
 const calendar = (id) => {
-  return TemporalHelpers.toPrimitiveObserver(actual, id, `calendar ${id}`);
+  const c = {};
+  TemporalHelpers.observeProperty(actual, c, "id", id, `calendar ${id}`);
+  return c;
 };
 
 const mdA = new Temporal.PlainMonthDay(2, 7, calendar("a"));
 const mdB = new Temporal.PlainMonthDay(2, 7, calendar("b"));
 const mdC = new Temporal.PlainMonthDay(2, 7, calendar("c"), 1974);
+actual.splice(0);  // disregard the HasProperty checks done in the constructor
 
 assert.sameValue(mdA.equals(mdC), false, "different year");
 assert.compareArray(actual, [], "Should not check calendar");

test/built-ins/Temporal/PlainMonthDay/prototype/toJSON/calendarname.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "05-02"],
-  [[{ toString() { return "custom"; } }], "1972-05-02[u-ca=custom]"],
+  [[{ id: "custom" }], "1972-05-02[u-ca=custom]"],
-  [[{ toString() { return "iso8601"; } }], "05-02"],
+  [[{ id: "iso8601" }], "05-02"],
-  [[{ toString() { return "ISO8601"; } }], "1972-05-02[u-ca=ISO8601]"],
+  [[{ id: "ISO8601" }], "1972-05-02[u-ca=ISO8601]"],
-  [[{ toString() { return "\u0131so8601"; } }], "1972-05-02[u-ca=\u0131so8601]"], // dotless i
+  [[{ id: "\u0131so8601" }], "1972-05-02[u-ca=\u0131so8601]"], // dotless i
 ];
 const options = {
   get calendarName() {

test/built-ins/Temporal/PlainMonthDay/prototype/toJSON/year-format.js

@@ -11,7 +11,7 @@ features: [Temporal]
 // the calendar is not ISO 8601
 class NotISO extends Temporal.Calendar {
   constructor() { super("iso8601"); }
-  toString() { return "not-iso"; }
+  get id() { return "not-iso"; }
 }
 const calendar = new NotISO();
 

test/built-ins/Temporal/PlainMonthDay/prototype/toString/calendar-tostring.js

@@ -4,14 +4,18 @@
 /*---
 esid: sec-temporal.plainmonthday.protoype.tostring
 description: Number of observable 'toString' calls on the calendar for each value of calendarName
+includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
 let calls;
 const customCalendar = {
-  toString() {
+  get id() {
     ++calls;
     return "custom";
+  },
+  toString() {
+    TemporalHelpers.assertUnreachable('toString should not be called');
   }
 };
 const monthday = new Temporal.PlainMonthDay(5, 2, customCalendar);
@@ -24,6 +28,6 @@ const monthday = new Temporal.PlainMonthDay(5, 2, customCalendar);
 ].forEach(([calendarName, expectedResult, expectedCalls]) => {
   calls = 0;
   const result = monthday.toString({ calendarName });
-  assert.sameValue(result, expectedResult, `toString output for calendarName = ${calendarName}`);
+  assert.sameValue(result, expectedResult, `id for calendarName = ${calendarName}`);
-  assert.sameValue(calls, expectedCalls, `calls to toString for calendarName = ${calendarName}`);
+  assert.sameValue(calls, expectedCalls, `calls to id getter for calendarName = ${calendarName}`);
 });

test/built-ins/Temporal/PlainMonthDay/prototype/toString/calendarname-always.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1972-05-02[u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1972-05-02[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1972-05-02[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1972-05-02[u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1972-05-02[u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1972-05-02[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1972-05-02[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1972-05-02[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1972-05-02[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainMonthDay/prototype/toString/calendarname-auto.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "05-02", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1972-05-02[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1972-05-02[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "05-02", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "05-02", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1972-05-02[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1972-05-02[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1972-05-02[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1972-05-02[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainMonthDay/prototype/toString/calendarname-critical.js

@@ -11,10 +11,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1972-05-02[!u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1972-05-02[!u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1972-05-02[!u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1972-05-02[!u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1972-05-02[!u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1972-05-02[!u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1972-05-02[!u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1972-05-02[!u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1972-05-02[!u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainMonthDay/prototype/toString/calendarname-never.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "05-02", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1972-05-02", "custom"],
+  [[{ id: "custom" }], "1972-05-02", "custom"],
-  [[{ toString() { return "iso8601"; } }], "05-02", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "05-02", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1972-05-02", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1972-05-02", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1972-05-02", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1972-05-02", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainMonthDay/prototype/toString/calendarname-undefined.js

@@ -16,10 +16,10 @@ features: [Temporal]
 
 const tests = [
   [[], "05-02", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1972-05-02[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1972-05-02[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "05-02", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "05-02", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1972-05-02[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1972-05-02[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1972-05-02[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1972-05-02[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainMonthDay/prototype/toString/calendarname-wrong-type.js

@@ -16,7 +16,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const monthday = new Temporal.PlainMonthDay(5, 2, calendar);
 

test/built-ins/Temporal/PlainMonthDay/prototype/toString/options-undefined.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "05-02"],
-  [[{ toString() { return "custom"; } }], "1972-05-02[u-ca=custom]"],
+  [[{ id: "custom" }], "1972-05-02[u-ca=custom]"],
-  [[{ toString() { return "iso8601"; } }], "05-02"],
+  [[{ id: "iso8601" }], "05-02"],
-  [[{ toString() { return "ISO8601"; } }], "1972-05-02[u-ca=ISO8601]"],
+  [[{ id: "ISO8601" }], "1972-05-02[u-ca=ISO8601]"],
-  [[{ toString() { return "\u0131so8601"; } }], "1972-05-02[u-ca=\u0131so8601]"], // dotless i
+  [[{ id: "\u0131so8601" }], "1972-05-02[u-ca=\u0131so8601]"], // dotless i
 ];
 
 for (const [args, expected] of tests) {

test/built-ins/Temporal/PlainMonthDay/prototype/toString/order-of-operations.js

@@ -12,9 +12,7 @@ const expected = [
   "get options.calendarName",
   "get options.calendarName.toString",
   "call options.calendarName.toString",
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
-  "call this.calendar.toString",
 ];
 const actual = [];
 

test/built-ins/Temporal/PlainMonthDay/prototype/toString/year-format.js

@@ -11,7 +11,7 @@ features: [Temporal]
 // the calendar is not ISO 8601
 class NotISO extends Temporal.Calendar {
   constructor() { super("iso8601"); }
-  toString() { return "not-iso"; }
+  get id() { return "not-iso"; }
 }
 const calendar = new NotISO();
 

test/built-ins/Temporal/PlainYearMonth/prototype/equals/compare-calendar.js

@@ -4,7 +4,7 @@
 /*---
 esid: sec-temporal.plainyearmonth.prototype.equals
 description: equals() takes the calendar into account
-includes: [compareArray.js]
+includes: [compareArray.js, temporalHelpers.js]
 features: [Temporal]
 ---*/
 
@@ -14,10 +14,13 @@ class CustomCalendar extends Temporal.Calendar {
     super("iso8601");
     this._id = id;
   }
-  toString() {
+  get id() {
     actual.push(this._id);
     return this._id;
   }
+  toString() {
+    TemporalHelpers.assertUnreachable("should not call toString");
+  }
 }
 
 const sharedCalendar = new CustomCalendar("a");

test/built-ins/Temporal/PlainYearMonth/prototype/since/mixed-calendar-invalid.js

@@ -12,7 +12,7 @@ class customCal extends Temporal.Calendar {
     super('iso8601');
   }
 
-  toString() {
+  get id() {
     return "I am a secret cal.";
   }
 }

test/built-ins/Temporal/PlainYearMonth/prototype/since/order-of-operations.js

@@ -26,12 +26,8 @@ const expected = [
   "get other.calendar.yearMonthFromFields",
   "call other.calendar.yearMonthFromFields",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/built-ins/Temporal/PlainYearMonth/prototype/toString/calendar-tostring.js

@@ -4,14 +4,18 @@
 /*---
 esid: sec-temporal.plainyearmonth.protoype.tostring
 description: Number of observable 'toString' calls on the calendar for each value of calendarName
+includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
 let calls;
 const customCalendar = {
-  toString() {
+  get id() {
     ++calls;
     return "custom";
+  },
+  toString() {
+    TemporalHelpers.assertUnreachable('toString should not be called');
   }
 };
 const yearmonth = new Temporal.PlainYearMonth(2000, 5, customCalendar);
@@ -24,6 +28,6 @@ const yearmonth = new Temporal.PlainYearMonth(2000, 5, customCalendar);
 ].forEach(([calendarName, expectedResult, expectedCalls]) => {
   calls = 0;
   const result = yearmonth.toString({ calendarName });
-  assert.sameValue(result, expectedResult, `toString output for calendarName = ${calendarName}`);
+  assert.sameValue(result, expectedResult, `id for calendarName = ${calendarName}`);
-  assert.sameValue(calls, expectedCalls, `calls to toString for calendarName = ${calendarName}`);
+  assert.sameValue(calls, expectedCalls, `calls to id getter for calendarName = ${calendarName}`);
 });

test/built-ins/Temporal/PlainYearMonth/prototype/toString/calendarname-always.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05-01[u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-01[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-01[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05-01[u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05-01[u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-01[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-01[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-01[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-01[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainYearMonth/prototype/toString/calendarname-auto.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-01[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-01[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-01[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-01[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-01[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-01[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainYearMonth/prototype/toString/calendarname-critical.js

@@ -11,10 +11,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05-01[!u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-01[!u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-01[!u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05-01[!u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05-01[!u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-01[!u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-01[!u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-01[!u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-01[!u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainYearMonth/prototype/toString/calendarname-never.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-01", "custom"],
+  [[{ id: "custom" }], "2000-05-01", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-01", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-01", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-01", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-01", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainYearMonth/prototype/toString/calendarname-undefined.js

@@ -16,10 +16,10 @@ features: [Temporal]
 
 const tests = [
   [[], "2000-05", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "2000-05-01[u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "2000-05-01[u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "2000-05", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "2000-05", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "2000-05-01[u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "2000-05-01[u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "2000-05-01[u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "2000-05-01[u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/PlainYearMonth/prototype/toString/calendarname-wrong-type.js

@@ -16,7 +16,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const yearmonth = new Temporal.PlainYearMonth(2000, 5, calendar);
 

test/built-ins/Temporal/PlainYearMonth/prototype/toString/options-undefined.js

@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const yearmonth1 = new Temporal.PlainYearMonth(2000, 5);
 const yearmonth2 = new Temporal.PlainYearMonth(2000, 5, calendar);

test/built-ins/Temporal/PlainYearMonth/prototype/toString/order-of-operations.js

@@ -12,9 +12,7 @@ const expected = [
   "get options.calendarName",
   "get options.calendarName.toString",
   "call options.calendarName.toString",
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
-  "call this.calendar.toString",
 ];
 const actual = [];
 

test/built-ins/Temporal/PlainYearMonth/prototype/until/mixed-calendar-invalid.js

@@ -12,7 +12,7 @@ class customCal extends Temporal.Calendar {
     super('iso8601');
   }
 
-  toString() {
+  get id() {
     return "I am a secret cal.";
   }
 }

test/built-ins/Temporal/PlainYearMonth/prototype/until/order-of-operations.js

@@ -26,12 +26,8 @@ const expected = [
   "get other.calendar.yearMonthFromFields",
   "call other.calendar.yearMonthFromFields",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/built-ins/Temporal/ZonedDateTime/prototype/equals/order-of-operations.js

@@ -65,12 +65,8 @@ const expected = [
   "get other.timeZone.toString",
   "call other.timeZone.toString",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
 ];
 const actual = [];
 

test/built-ins/Temporal/ZonedDateTime/prototype/since/order-of-operations.js

@@ -56,12 +56,8 @@ const expected = [
   "get other.timeZone.getOffsetNanosecondsFor",
   "call other.timeZone.getOffsetNanosecondsFor",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/built-ins/Temporal/ZonedDateTime/prototype/toString/calendar-tostring.js

@@ -4,14 +4,18 @@
 /*---
 esid: sec-temporal.zoneddatetime.protoype.tostring
 description: Number of observable 'toString' calls on the calendar for each value of calendarName
+includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
 let calls;
 const customCalendar = {
-  toString() {
+  get id() {
     ++calls;
     return "custom";
+  },
+  toString() {
+    TemporalHelpers.assertUnreachable('toString should not be called');
   }
 };
 const date = new Temporal.ZonedDateTime(1_000_000_000_987_654_321n, "UTC", customCalendar);
@@ -24,6 +28,6 @@ const date = new Temporal.ZonedDateTime(1_000_000_000_987_654_321n, "UTC", custo
 ].forEach(([calendarName, expectedResult, expectedCalls]) => {
   calls = 0;
   const result = date.toString({ calendarName });
-  assert.sameValue(result, expectedResult, `toString output for calendarName = ${calendarName}`);
+  assert.sameValue(result, expectedResult, `id for calendarName = ${calendarName}`);
-  assert.sameValue(calls, expectedCalls, `calls to toString for calendarName = ${calendarName}`);
+  assert.sameValue(calls, expectedCalls, `calls to id getter for calendarName = ${calendarName}`);
 });

test/built-ins/Temporal/ZonedDateTime/prototype/toString/calendarname-always.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/ZonedDateTime/prototype/toString/calendarname-auto.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1970-01-01T01:01:01.987654321+00:00[UTC]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/ZonedDateTime/prototype/toString/calendarname-critical.js

@@ -11,10 +11,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=iso8601]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=iso8601]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=iso8601]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][!u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/ZonedDateTime/prototype/toString/calendarname-never.js

@@ -9,10 +9,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1970-01-01T01:01:01.987654321+00:00[UTC]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom"],
+  [[{ id: "custom" }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/ZonedDateTime/prototype/toString/calendarname-undefined.js

@@ -16,10 +16,10 @@ features: [Temporal]
 
 const tests = [
   [[], "1970-01-01T01:01:01.987654321+00:00[UTC]", "built-in ISO"],
-  [[{ toString() { return "custom"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=custom]", "custom"],
+  [[{ id: "custom" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=custom]", "custom"],
-  [[{ toString() { return "iso8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with iso8601 toString"],
+  [[{ id: "iso8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC]", "custom with iso8601 id"],
-  [[{ toString() { return "ISO8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=ISO8601]", "custom with caps toString"],
+  [[{ id: "ISO8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=ISO8601]", "custom with caps id"],
-  [[{ toString() { return "\u0131so8601"; } }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=\u0131so8601]", "custom with dotless i toString"],
+  [[{ id: "\u0131so8601" }], "1970-01-01T01:01:01.987654321+00:00[UTC][u-ca=\u0131so8601]", "custom with dotless i id"],
 ];
 
 for (const [args, expected, description] of tests) {

test/built-ins/Temporal/ZonedDateTime/prototype/toString/calendarname-wrong-type.js

@@ -16,7 +16,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const datetime = new Temporal.ZonedDateTime(1_000_000_000_987_654_321n, "UTC", calendar);
 

test/built-ins/Temporal/ZonedDateTime/prototype/toString/options-undefined.js

@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 const calendar = {
-  toString() { return "custom"; }
+  id: "custom",
 };
 const datetime1 = new Temporal.ZonedDateTime(957270896_987_650_000n, "UTC");
 const datetime2 = new Temporal.ZonedDateTime(957270896_987_650_000n, "UTC", calendar);

test/built-ins/Temporal/ZonedDateTime/prototype/toString/order-of-operations.js

@@ -34,9 +34,7 @@ const expected = [
   "get this.timeZone[Symbol.toPrimitive]",
   "get this.timeZone.toString",
   "call this.timeZone.toString",
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
-  "call this.calendar.toString",
 ];
 const actual = [];
 
@@ -84,9 +82,7 @@ const expectedForFractionalSecondDigits = [
   "get this.timeZone[Symbol.toPrimitive]",
   "get this.timeZone.toString",
   "call this.timeZone.toString",
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
-  "call this.calendar.toString",
 ];
 
 instance.toString(

test/built-ins/Temporal/ZonedDateTime/prototype/until/order-of-operations.js

@@ -56,12 +56,8 @@ const expected = [
   "get other.timeZone.getOffsetNanosecondsFor",
   "call other.timeZone.getOffsetNanosecondsFor",
   // CalendarEquals
-  "get this.calendar[Symbol.toPrimitive]",
+  "get this.calendar.id",
-  "get this.calendar.toString",
+  "get other.calendar.id",
-  "call this.calendar.toString",
-  "get other.calendar[Symbol.toPrimitive]",
-  "get other.calendar.toString",
-  "call other.calendar.toString",
   // CopyDataProperties
   "ownKeys options",
   "getOwnPropertyDescriptor options.roundingIncrement",

test/intl402/Temporal/PlainDateTime/prototype/withPlainDate/argument-plaindate-calendar-same-id.js

@@ -9,13 +9,14 @@ includes: [temporalHelpers.js]
 ---*/
 
 const cal1 = {
-  toString() { return "this is a string"; },
+  id: "this is a string",
+  toString() { return "this is a another string"; },
 };
 const cal2 = {
-  id: 'thisisnotiso',
+  id: "this is a string",
   era() { return "the era"; },
   eraYear() { return 1909; },
-  toString() { return "this is a string"; },
+  toString() { return "thisisnotiso"; },
   year() { return 2008; },
   month() { return 9; },
   monthCode() { return "M09"; },

test/intl402/Temporal/PlainDateTime/prototype/withPlainDate/argument-plaindate-calendar-same-object.js

@@ -10,7 +10,10 @@ includes: [temporalHelpers.js]
 
 let calls = 0;
 const cal = {
-  id: 'thisisnotiso',
+  get id() {
+    ++calls;
+    return "thisisnotiso";
+  },
   era() { return "the era"; },
   eraYear() { return 1909; },
   toString() {
@@ -39,4 +42,4 @@ assert.sameValue(
   cal,
   "calendar is unchanged with same calendars (2)"
 );
-assert.sameValue(calls, 0, "should not have called cal.toString()");
+assert.sameValue(calls, 0, "should not have called cal.toString() or accessed cal.id");

test/staging/Temporal/Instant/old/toZonedDateTime.js

@@ -15,7 +15,7 @@ assert.throws(TypeError, () => inst.toZonedDateTime());
 // throws with a string parameter
 assert.throws(TypeError, () => inst.toZonedDateTime("UTC"));
 
-var fakeGregorian = { toString() { return "gregory"; }};
+var fakeGregorian = { id: "gregory" };
 
 // time zone parameter UTC
 var timeZone = Temporal.TimeZone.from("UTC");

test/staging/Temporal/UserCalendar/old/calendar-extra-fields.js

@@ -11,6 +11,9 @@ class SeasonCalendar extends Temporal.Calendar {
   constructor() {
     super("iso8601");
   }
+  get id() {
+    return "season";
+  }
   toString() {
     return "season";
   }

test/staging/Temporal/UserCalendar/old/calendar-non-trivial-mergefields.js

@@ -11,6 +11,9 @@ class CenturyCalendar extends Temporal.Calendar {
   constructor() {
     super("iso8601");
   }
+  get id() {
+    return 'century';
+  }
   toString() {
     return "century";
   }

test/staging/Temporal/UserCalendar/old/trivial-protocol-implementation.js

@@ -37,6 +37,7 @@ function isoToDecimal(date) {
   };
 }
 var obj = {
+  id: 'decimal',
   toString() {
     return "decimal";
   },

test/staging/Temporal/UserTimezone/old/subminute-offset.js

@@ -50,7 +50,7 @@ assert.throws(RangeError, () => Temporal.TimeZone.from("2020-05-26T16:02:46.2511
 assert.sameValue(obj.getOffsetStringFor(inst), "-00:00:01.111111111")
 
 // converts to DateTime
-var fakeGregorian = { toString() { return "gregory"; }};
+var fakeGregorian = { id: "gregory" };
 assert.sameValue(`${ obj.getPlainDateTimeFor(inst) }`, "1969-12-31T23:59:58.888888889");
 assert.sameValue(`${ obj.getPlainDateTimeFor(inst, fakeGregorian) }`, "1969-12-31T23:59:58.888888889[u-ca=gregory]");
 

test/staging/Temporal/UserTimezone/old/trivial-protocol.js

@@ -32,7 +32,7 @@ var zdt = new Temporal.ZonedDateTime(0n, obj);
 assert.sameValue(zdt.toString(), "1970-01-01T00:00:00+00:00[Etc/Custom/UTC_Protocol]");
 
 // works in Temporal.Now
-var fakeGregorian = { toString() { return "gregory"; }};
+var fakeGregorian = { id: "gregory" };
 assert(Temporal.Now.plainDateTimeISO(obj) instanceof Temporal.PlainDateTime);
 assert(Temporal.Now.plainDateTime(fakeGregorian, obj) instanceof Temporal.PlainDateTime);
 assert(Temporal.Now.plainDateISO(obj) instanceof Temporal.PlainDate);

test/staging/Temporal/UserTimezone/old/trivial-subclass.js

@@ -88,7 +88,7 @@ assert.throws(RangeError, () => Temporal.TimeZone.from("2020-05-26T16:02:46.2511
 assert.sameValue(obj.getOffsetStringFor(inst), "+00:00")
 
 // converts to DateTime
-var fakeGregorian = { toString() { return "gregory"; }};
+var fakeGregorian = { id: "gregory" };
 assert.sameValue(`${ obj.getPlainDateTimeFor(inst) }`, "1970-01-01T00:00:00");
 assert.sameValue(`${ obj.getPlainDateTimeFor(inst, fakeGregorian) }`, "1970-01-01T00:00:00[u-ca=gregory]");
 

test/staging/Temporal/ZonedDateTime/old/construction-and-properties.js

@@ -66,7 +66,7 @@ var fakeGregorian = {
   daysInYear(date) { return date.withCalendar("iso8601").daysInYear; },
   monthsInYear(date) { return date.withCalendar("iso8601").monthsInYear; },
   inLeapYear(date) { return date.withCalendar("iso8601").inLeapYear; },
-  toString() { return "gregory"; },
+  id: "gregory",
 };
 var fakeVienna = {
   getOffsetNanosecondsFor() { return 3600_000_000_000; },

test/staging/Temporal/ZonedDateTime/old/equals.js

@@ -13,7 +13,7 @@ var tz = {
 };
 var cal = {
   dateFromFields(...args) { return Temporal.Calendar.from("iso8601").dateFromFields(...args); },
-  toString() { return "gregory"; },
+  id: "gregory",
   fields(fieldNames) { return fieldNames; },
 };
 var zdt = new Temporal.ZonedDateTime(0n, tz, cal);

test/staging/Temporal/ZonedDateTime/old/since.js

@@ -87,7 +87,7 @@ assert.notSameValue(monthsDifference.months, 0);
 
 // no two different calendars
 var zdt1 = new Temporal.ZonedDateTime(0n, "UTC");
-var fakeJapanese = { toString() { return "japanese"; }};
+var fakeJapanese = { id: "japanese" };
 var zdt2 = new Temporal.ZonedDateTime(0n, "UTC", fakeJapanese);
 assert.throws(RangeError, () => zdt1.since(zdt2));
 

test/staging/Temporal/ZonedDateTime/old/toPlainDate.js

@@ -14,7 +14,7 @@ var zdt = Temporal.Instant.from("2019-10-29T09:46:38.271986102Z").toZonedDateTim
 assert.sameValue(`${ zdt.toPlainDate() }`, "2019-10-29");
 
 // preserves the calendar
-const fakeGregorian = { toString() { return "gregory" }};
+const fakeGregorian = { id: 'gregory' };
 var zdt = Temporal.Instant.from("2019-10-29T09:46:38.271986102Z").toZonedDateTime({
   timeZone: tz,
   calendar: fakeGregorian

test/staging/Temporal/ZonedDateTime/old/toPlainMonthDay.js

@@ -15,6 +15,7 @@ assert.sameValue(`${ zdt.toPlainMonthDay() }`, "10-29");
 
 // preserves the calendar
 var fakeGregorian = {
+  id: 'gregory',
   monthDayFromFields(fields) {
     var md = Temporal.Calendar.from("iso8601").monthDayFromFields(fields);
     var {isoYear, isoMonth, isoDay} = md.getISOFields();
@@ -22,7 +23,6 @@ var fakeGregorian = {
   },
   monthCode(date) { return date.withCalendar("iso8601").monthCode; },
   day(date) { return date.withCalendar("iso8601").day; },
-  toString() { return "gregory"; },
   fields(fieldNames) { return fieldNames; },
 };
 var zdt = Temporal.Instant.from("2019-10-29T09:46:38.271986102Z").toZonedDateTime({

test/staging/Temporal/ZonedDateTime/old/toPlainYearMonth.js

@@ -15,6 +15,7 @@ assert.sameValue(`${ zdt.toPlainYearMonth() }`, "2019-10");
 
 // preserves the calendar
 var fakeGregorian = {
+  id: 'gregory',
   yearMonthFromFields(fields) {
     var ym = Temporal.Calendar.from("iso8601").yearMonthFromFields(fields);
     var {isoYear, isoMonth, isoDay} = ym.getISOFields();
@@ -22,7 +23,6 @@ var fakeGregorian = {
   },
   year(date) { return date.withCalendar("iso8601").year; },
   monthCode(date) { return date.withCalendar("iso8601").monthCode; },
-  toString() { return "gregory"; },
   fields(fieldNames) { return fieldNames; },
 };
 var zdt = Temporal.Instant.from("2019-10-29T09:46:38.271986102Z").toZonedDateTime({

test/staging/Temporal/ZonedDateTime/old/toString.js

@@ -9,7 +9,7 @@ features: [Temporal]
 ---*/
 
 var zdt1 = Temporal.ZonedDateTime.from("1976-11-18T15:23+00:00[UTC]");
-var fakeGregorian = { toString() { return "gregory" }};
+var fakeGregorian = { id: "gregory" };
 
 // shows offset if offset = auto
 assert.sameValue(zdt1.toString({ offset: "auto" }), "1976-11-18T15:23:00+00:00[UTC]");

test/staging/Temporal/ZonedDateTime/old/until.js

@@ -87,7 +87,7 @@ assert.notSameValue(monthsDifference.months, 0);
 
 // no two different calendars
 var zdt1 = new Temporal.ZonedDateTime(0n, "UTC");
-var fakeJapanese = { toString() { return "japanese"; }};
+var fakeJapanese = { id: "japanese" };
 var zdt2 = new Temporal.ZonedDateTime(0n, "UTC", fakeJapanese);
 assert.throws(RangeError, () => zdt1.until(zdt2));
 

test/staging/Temporal/ZonedDateTime/old/withCalendar.js

@@ -10,7 +10,7 @@ features: [Temporal]
 var zdt = Temporal.ZonedDateTime.from("2019-11-18T15:23:30.123456789-08:00[-08:00]");
 
 // zonedDateTime.withCalendar(japanese) works
-var cal = { toString() { return "japanese"; }};
+var cal = { id: 'japanese', toString() { return 'japanese'; } };
 assert.sameValue(`${ zdt.withCalendar(cal) }`, "2019-11-18T15:23:30.123456789-08:00[-08:00][u-ca=japanese]");
 
 // keeps instant and time zone the same

test/staging/Temporal/ZonedDateTime/old/withPlainDate.js

@@ -27,7 +27,7 @@ assert.sameValue(`${ zdt.withPlainDate(date) }`, "2020-01-23T03:24:30-08:00[Cust
 assert.sameValue(`${ zdt.withPlainDate("2018-09-15") }`, "2018-09-15T03:24:30-08:00[Custom/Spring_Fall]");
 
 // result contains a non-ISO calendar if present in the input
-var fakeJapanese = { toString() { return "japanese"; }};
+var fakeJapanese = { id: "japanese" };
 assert.sameValue(`${ zdt.withCalendar(fakeJapanese).withPlainDate("2008-09-06") }`, "2008-09-06T03:24:30-08:00[Custom/Spring_Fall][u-ca=japanese]");
 
 // calendar is unchanged if input has ISO calendar
@@ -35,7 +35,7 @@ var date = new Temporal.PlainDate(2008, 9, 6, fakeJapanese);
 assert.sameValue(`${ zdt.withPlainDate(date) }`, "2008-09-06T03:24:30-08:00[Custom/Spring_Fall][u-ca=japanese]");
 
 // throws if both `this` and `other` have a non-ISO calendar
-var fakeGregorian = { toString() { return "gregory"; }};
+var fakeGregorian = { id: "gregory" };
 assert.throws(RangeError, () => zdt.withCalendar(fakeGregorian).withPlainDate(date));
 
 // object must contain at least one correctly-spelled property

test/staging/Temporal/ZonedDateTime/old/withTimezone.js

@@ -8,7 +8,7 @@ features: [Temporal]
 ---*/
 
 // keeps instant and calendar the same
-var fakeGregorian = { toString() { return "gregory"; }};
+var fakeGregorian = { id: 'gregory' };
 var zdt = Temporal.ZonedDateTime.from("2019-11-18T15:23:30.123456789+01:00[+01:00]").withCalendar(fakeGregorian);
 var zdt2 = zdt.withTimeZone("-08:00");
 assert.sameValue(zdt.epochNanoseconds, zdt2.epochNanoseconds);