Temporal operation NanosecondsToDays: Test infinite or arbitrary-length observable loops in Duration and ZonedDateTime

harness/temporalHelpers.js

@@ -1382,6 +1382,20 @@ var TemporalHelpers = {
     });
   },
 
+  /*
+   * observeMethod(calls, object, propertyName, value):
+   *
+   * Defines an own property @object.@propertyName with value @value, that
+   * will log any calls of @value to the array @calls.
+   */
+  observeMethod(calls, object, propertyName, objectName = "") {
+    const method = object[propertyName];
+    object[propertyName] = function () {
+      calls.push(`call ${formatPropertyName(propertyName, objectName)}`);
+      return method.apply(object, arguments);
+    };
+  },
+
   /*
    * Used for substituteMethod to indicate default behavior instead of a
    * substituted value

test/built-ins/Temporal/Duration/prototype/add/nanoseconds-to-days-loop-indefinitely-1.js

@@ -0,0 +1,58 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.add
+description: >
+  NanosecondsToDays can loop arbitrarily long, performing observable operations each iteration.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  15. If sign is 1, then
+    a. Repeat, while days > 0 and intermediateNs > endNs,
+        i. Set days to days - 1.
+        ii. Set intermediateNs to ℝ(? AddZonedDateTime(ℤ(startNs), relativeTo.[[TimeZone]],
+            relativeTo.[[Calendar]], 0, 0, 0, days, 0, 0, 0, 0, 0, 0)).
+  ...
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
+
+function createRelativeTo(count) {
+  const tz = new Temporal.TimeZone("UTC");
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, tz, "getPossibleInstantsFor");
+  const cal = new Temporal.Calendar("iso8601");
+  // Return _count_ days for the second call to dateUntil, behaving normally after
+  TemporalHelpers.substituteMethod(cal, "dateUntil", [
+    TemporalHelpers.SUBSTITUTE_SKIP,
+    Temporal.Duration.from({ days: count }),
+  ]);
+  return new Temporal.ZonedDateTime(0n, tz, cal);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.add(duration, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  200 + 2,
+  "Expected duration.add to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.add(duration, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 2,
+  "Expected duration.add to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/Duration/prototype/add/nanoseconds-to-days-loop-indefinitely-2.js

@@ -0,0 +1,71 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.add
+description: >
+  NanosecondsToDays can loop infinitely.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  18. Repeat, while done is false,
+    a. Let oneDayFartherNs be ℝ(? AddZonedDateTime(ℤ(intermediateNs), relativeTo.[[TimeZone]],
+       relativeTo.[[Calendar]], 0, 0, 0, sign, 0, 0, 0, 0, 0, 0)).
+    b. Set dayLengthNs to oneDayFartherNs - intermediateNs.
+    c. If (nanoseconds - dayLengthNs) × sign ≥ 0, then
+        i. Set nanoseconds to nanoseconds - dayLengthNs.
+        ii. Set intermediateNs to oneDayFartherNs.
+        iii. Set days to days + sign.
+    d. Else,
+        i. Set done to true.
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
+
+function createRelativeTo(count) {
+  const dayLengthNs = 86400000000000n;
+  const dayInstant = new Temporal.Instant(dayLengthNs);
+  const substitutions = [];
+  const timeZone = new Temporal.TimeZone("UTC");
+  // Return constant value for first _count_ calls
+  TemporalHelpers.substituteMethod(
+    timeZone,
+    "getPossibleInstantsFor",
+    substitutions
+  );
+  substitutions.length = count;
+  let i = 0;
+  for (i = 0; i < substitutions.length; i++) {
+    // (this value)
+    substitutions[i] = [dayInstant];
+  }
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, timeZone, "getPossibleInstantsFor");
+  return new Temporal.ZonedDateTime(0n, timeZone);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.add(duration, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  200 + 1,
+  "Expected duration.add to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.add(duration, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 1,
+  "Expected duration.add to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/Duration/prototype/round/nanoseconds-to-days-loop-indefinitely-1.js

@@ -1,10 +1,9 @@
 // Copyright (C) 2022 André Bargull. All rights reserved.
 // This code is governed by the BSD license found in the LICENSE file.
-
 /*---
 esid: sec-temporal.duration.prototype.round
 description: >
-  NanosecondsToDays can loop indefinitely.
+  NanosecondsToDays can loop arbitrarily long, performing observable operations each iteration.
 info: |
   NanosecondsToDays ( nanoseconds, relativeTo )
 
@@ -19,54 +18,41 @@ includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
-// Intentionally not Test262Error to ensure assertion errors are correctly propagated.
-class StopExecution extends Error {}
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
 
-const stopAt = 1000;
+function createRelativeTo(count) {
+  const tz = new Temporal.TimeZone("UTC");
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, tz, "getPossibleInstantsFor");
+  const cal = new Temporal.Calendar("iso8601");
+  // Return _count_ days for the first call to dateUntil, behaving normally after
+  TemporalHelpers.substituteMethod(cal, "dateUntil", [
+    Temporal.Duration.from({ days: count }),
+  ]);
+  return new Temporal.ZonedDateTime(0n, tz, cal);
+}
 
-// Always add two days to the start date, this ensures the intermediate date
-// is larger than the end date.
-let twoDays = Temporal.Duration.from({days: 2});
-
-// Number of calls to dateAdd.
-let count = 0;
-
-let cal = new class extends Temporal.Calendar {
-  // Set `days` to a number larger than `Number.MAX_SAFE_INTEGER`.
-  dateUntil(start, end, options) {
-    return Temporal.Duration.from({days: Number.MAX_VALUE});
-  }
-
-  dateAdd(date, duration, options) {
-    // Stop when we've reached the test limit.
-    count += 1;
-    if (count === stopAt) {
-      throw new StopExecution();
-    }
-
-    if (count === 1) {
-      return Temporal.Calendar.prototype.dateAdd.call(this, date, duration, options);
-    }
-
-    TemporalHelpers.assertPlainDate(date, 1970, 1, "M01", 1);
-
-    TemporalHelpers.assertDuration(
-      duration,
-      0, 0, 0, Number.MAX_VALUE,
-      0, 0, 0,
-      0, 0, 0,
-    );
-
-    return Temporal.Calendar.prototype.dateAdd.call(this, date, twoDays, options);
-  }
-}("iso8601");
-
-let zdt = new Temporal.ZonedDateTime(0n, "UTC", cal);
-let duration = Temporal.Duration.from({days: 1});
-let options = {
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.round({
   largestUnit: "days",
   relativeTo: zdt,
-};
+});
+assert.sameValue(
+  calls.length,
+  200 + 2,
+  "Expected duration.round to call getPossibleInstantsFor correct number of times"
+);
 
-assert.throws(StopExecution, () => duration.round(options));
-assert.sameValue(count, stopAt);
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.round({
+  largestUnit: "days",
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 2,
+  "Expected duration.round to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/Duration/prototype/round/nanoseconds-to-days-loop-indefinitely-2.js

@@ -1,10 +1,9 @@
 // Copyright (C) 2022 André Bargull. All rights reserved.
 // This code is governed by the BSD license found in the LICENSE file.
-
 /*---
 esid: sec-temporal.duration.prototype.round
 description: >
-  NanosecondsToDays can loop indefinitely.
+  NanosecondsToDays can loop infinitely.
 info: |
   NanosecondsToDays ( nanoseconds, relativeTo )
 
@@ -23,43 +22,51 @@ includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
-// Intentionally not Test262Error to ensure assertion errors are correctly propagated.
-class StopExecution extends Error {}
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
 
-const stopAt = 1000;
-
-// Number of calls to getPossibleInstantsFor.
-let count = 0;
-
-// UTC time zones so we don't have to worry about time zone offsets.
-let tz = new class extends Temporal.TimeZone {
-  getPossibleInstantsFor(dt) {
-    // Stop when we've reached the test limit.
-    count += 1;
-    if (count === stopAt) {
-      throw new StopExecution();
-    }
-
-    if (count < 4) {
-      // The first couple calls request the instant for 1970-01-02.
-      TemporalHelpers.assertPlainDateTime(dt, 1970, 1, "M01", 2, 0, 0, 0, 0, 0, 0);
-    } else {
-      // Later on the instant for 1970-01-03 is requested.
-      TemporalHelpers.assertPlainDateTime(dt, 1970, 1, "M01", 3, 0, 0, 0, 0, 0, 0);
-    }
-
-    // Always return "1970-01-02T00:00:00Z". This leads to iterating indefinitely
-    // in NanosecondsToDays.
-    return [new Temporal.Instant(86400000000000n)];
+function createRelativeTo(count) {
+  const dayLengthNs = 86400000000000n;
+  const dayInstant = new Temporal.Instant(dayLengthNs);
+  const substitutions = [];
+  const timeZone = new Temporal.TimeZone("UTC");
+  // Return constant value for first _count_ calls
+  TemporalHelpers.substituteMethod(
+    timeZone,
+    "getPossibleInstantsFor",
+    substitutions
+  );
+  substitutions.length = count;
+  let i = 0;
+  for (i = 0; i < substitutions.length; i++) {
+    // (this value)
+    substitutions[i] = [dayInstant];
   }
-}("UTC");
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, timeZone, "getPossibleInstantsFor");
+  return new Temporal.ZonedDateTime(0n, timeZone);
+}
 
-let zdt = new Temporal.ZonedDateTime(0n, tz);
-let duration = Temporal.Duration.from({days: 1});
-let options = {
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.round({
   smallestUnit: "days",
   relativeTo: zdt,
-};
+});
+assert.sameValue(
+  calls.length,
+  200 + 1,
+  "Expected duration.round to call getPossibleInstantsFor correct number of times"
+);
 
-assert.throws(StopExecution, () => duration.round(options));
-assert.sameValue(count, stopAt);
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.round({
+  smallestUnit: "days",
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 1,
+  "Expected duration.round to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/Duration/prototype/subtract/nanoseconds-to-days-loop-indefinitely-1.js

@@ -0,0 +1,59 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.subtract
+description: >
+  NanosecondsToDays can loop arbitrarily long, performing observable operations each iteration.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  15. If sign is 1, then
+    a. Repeat, while days > 0 and intermediateNs > endNs,
+        i. Set days to days - 1.
+        ii. Set intermediateNs to ℝ(? AddZonedDateTime(ℤ(startNs), relativeTo.[[TimeZone]],
+            relativeTo.[[Calendar]], 0, 0, 0, days, 0, 0, 0, 0, 0, 0)).
+  ...
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
+const other = Temporal.Duration.from({ hours: 1 });
+
+function createRelativeTo(count) {
+  const tz = new Temporal.TimeZone("UTC");
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, tz, "getPossibleInstantsFor");
+  const cal = new Temporal.Calendar("iso8601");
+  // Return _count_ days for the second call to dateUntil, behaving normally after
+  TemporalHelpers.substituteMethod(cal, "dateUntil", [
+    TemporalHelpers.SUBSTITUTE_SKIP,
+    Temporal.Duration.from({ days: count }),
+  ]);
+  return new Temporal.ZonedDateTime(0n, tz, cal);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.subtract(other, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  200 + 2,
+  "Expected duration.subtract to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.subtract(other, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 2,
+  "Expected duration.subtract to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/Duration/prototype/subtract/nanoseconds-to-days-loop-indefinitely-2.js

@@ -0,0 +1,71 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.subtract
+description: >
+  NanosecondsToDays can loop infinitely.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  18. Repeat, while done is false,
+    a. Let oneDayFartherNs be ℝ(? AddZonedDateTime(ℤ(intermediateNs), relativeTo.[[TimeZone]],
+       relativeTo.[[Calendar]], 0, 0, 0, sign, 0, 0, 0, 0, 0, 0)).
+    b. Set dayLengthNs to oneDayFartherNs - intermediateNs.
+    c. If (nanoseconds - dayLengthNs) × sign ≥ 0, then
+        i. Set nanoseconds to nanoseconds - dayLengthNs.
+        ii. Set intermediateNs to oneDayFartherNs.
+        iii. Set days to days + sign.
+    d. Else,
+        i. Set done to true.
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
+
+function createRelativeTo(count) {
+  const dayLengthNs = 86400000000000n;
+  const dayInstant = new Temporal.Instant(dayLengthNs);
+  const substitutions = [];
+  const timeZone = new Temporal.TimeZone("UTC");
+  // Return constant value for first _count_ calls
+  TemporalHelpers.substituteMethod(
+    timeZone,
+    "getPossibleInstantsFor",
+    substitutions
+  );
+  substitutions.length = count;
+  let i = 0;
+  for (i = 0; i < substitutions.length; i++) {
+    // (this value)
+    substitutions[i] = [dayInstant];
+  }
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, timeZone, "getPossibleInstantsFor");
+  return new Temporal.ZonedDateTime(0n, timeZone);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.subtract(duration, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  200 + 1,
+  "Expected duration.subtract to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.subtract(duration, {
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 1,
+  "Expected duration.subtract to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/Duration/prototype/total/nanoseconds-to-days-loop-indefinitely-1.js

@@ -0,0 +1,59 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.total
+description: >
+  NanosecondsToDays can loop arbitrarily long, performing observable operations each iteration.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  15. If sign is 1, then
+    a. Repeat, while days > 0 and intermediateNs > endNs,
+        i. Set days to days - 1.
+        ii. Set intermediateNs to ℝ(? AddZonedDateTime(ℤ(startNs), relativeTo.[[TimeZone]],
+            relativeTo.[[Calendar]], 0, 0, 0, days, 0, 0, 0, 0, 0, 0)).
+  ...
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
+
+function createRelativeTo(count) {
+  const tz = new Temporal.TimeZone("UTC");
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, tz, "getPossibleInstantsFor");
+  const cal = new Temporal.Calendar("iso8601");
+  // Return _count_ days for the first call to dateUntil, behaving normally after
+  TemporalHelpers.substituteMethod(cal, "dateUntil", [
+    Temporal.Duration.from({ days: count }),
+  ]);
+  return new Temporal.ZonedDateTime(0n, tz, cal);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.total({
+  unit: "day",
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  200 + 3,
+  "Expected duration.total to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.total({
+  unit: "day",
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 3,
+  "Expected duration.total to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/Duration/prototype/total/nanoseconds-to-days-loop-indefinitely-2.js

@@ -0,0 +1,73 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.total
+description: >
+  NanosecondsToDays can loop infinitely.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  18. Repeat, while done is false,
+    a. Let oneDayFartherNs be ℝ(? AddZonedDateTime(ℤ(intermediateNs), relativeTo.[[TimeZone]],
+       relativeTo.[[Calendar]], 0, 0, 0, sign, 0, 0, 0, 0, 0, 0)).
+    b. Set dayLengthNs to oneDayFartherNs - intermediateNs.
+    c. If (nanoseconds - dayLengthNs) × sign ≥ 0, then
+        i. Set nanoseconds to nanoseconds - dayLengthNs.
+        ii. Set intermediateNs to oneDayFartherNs.
+        iii. Set days to days + sign.
+    d. Else,
+        i. Set done to true.
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const duration = Temporal.Duration.from({ days: 1 });
+
+function createRelativeTo(count) {
+  const dayLengthNs = 86400000000000n;
+  const dayInstant = new Temporal.Instant(dayLengthNs);
+  const substitutions = [];
+  const timeZone = new Temporal.TimeZone("UTC");
+  // Return constant value for first _count_ calls
+  TemporalHelpers.substituteMethod(
+    timeZone,
+    "getPossibleInstantsFor",
+    substitutions
+  );
+  substitutions.length = count;
+  let i = 0;
+  for (i = 0; i < substitutions.length; i++) {
+    // (this value)
+    substitutions[i] = [dayInstant];
+  }
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, timeZone, "getPossibleInstantsFor");
+  return new Temporal.ZonedDateTime(0n, timeZone);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+duration.total({
+  unit: "day",
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  200 + 2,
+  "Expected duration.total to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+duration.total({
+  unit: "day",
+  relativeTo: zdt,
+});
+assert.sameValue(
+  calls.length,
+  300 + 2,
+  "Expected duration.total to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/ZonedDateTime/prototype/since/nanoseconds-to-days-loop-indefinitely-1.js

@@ -0,0 +1,59 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.since
+description: >
+  NanosecondsToDays can loop arbitrarily long, performing observable operations each iteration.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  15. If sign is 1, then
+    a. Repeat, while days > 0 and intermediateNs > endNs,
+        i. Set days to days - 1.
+        ii. Set intermediateNs to ℝ(? AddZonedDateTime(ℤ(startNs), relativeTo.[[TimeZone]],
+            relativeTo.[[Calendar]], 0, 0, 0, days, 0, 0, 0, 0, 0, 0)).
+  ...
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const dayLengthNs = 86400000000000n;
+const other = new Temporal.ZonedDateTime(dayLengthNs, "UTC", "iso8601");
+
+function createRelativeTo(count) {
+  const tz = new Temporal.TimeZone("UTC");
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, tz, "getPossibleInstantsFor");
+  const cal = new Temporal.Calendar("iso8601");
+  // Return _count_ days for the second call to dateUntil, behaving normally after
+  TemporalHelpers.substituteMethod(cal, "dateUntil", [
+    TemporalHelpers.SUBSTITUTE_SKIP,
+    Temporal.Duration.from({ days: count }),
+  ]);
+  return new Temporal.ZonedDateTime(0n, tz, cal);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+zdt.since(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  200 + 1,
+  "Expected ZonedDateTime.since to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+zdt.since(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  300 + 1,
+  "Expected ZonedDateTime.since to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/ZonedDateTime/prototype/since/nanoseconds-to-days-loop-indefinitely-2.js

@@ -0,0 +1,71 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.since
+description: >
+  NanosecondsToDays can loop infinitely.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  18. Repeat, while done is false,
+    a. Let oneDayFartherNs be ℝ(? AddZonedDateTime(ℤ(intermediateNs), relativeTo.[[TimeZone]],
+       relativeTo.[[Calendar]], 0, 0, 0, sign, 0, 0, 0, 0, 0, 0)).
+    b. Set dayLengthNs to oneDayFartherNs - intermediateNs.
+    c. If (nanoseconds - dayLengthNs) × sign ≥ 0, then
+        i. Set nanoseconds to nanoseconds - dayLengthNs.
+        ii. Set intermediateNs to oneDayFartherNs.
+        iii. Set days to days + sign.
+    d. Else,
+        i. Set done to true.
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const dayLengthNs = 86400000000000n;
+const other = new Temporal.ZonedDateTime(dayLengthNs, "UTC", "iso8601");
+
+function createRelativeTo(count) {
+  const dayInstant = new Temporal.Instant(dayLengthNs);
+  const substitutions = [];
+  const timeZone = new Temporal.TimeZone("UTC");
+  // Return constant value for first _count_ calls
+  TemporalHelpers.substituteMethod(
+    timeZone,
+    "getPossibleInstantsFor",
+    substitutions
+  );
+  substitutions.length = count;
+  let i = 0;
+  for (i = 0; i < substitutions.length; i++) {
+    // (this value)
+    substitutions[i] = [dayInstant];
+  }
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, timeZone, "getPossibleInstantsFor");
+  return new Temporal.ZonedDateTime(0n, timeZone);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+zdt.since(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  200 + 1,
+  "Expected ZonedDateTime.since to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+zdt.since(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  300 + 1,
+  "Expected ZonedDateTime.since to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/ZonedDateTime/prototype/until/nanoseconds-to-days-loop-indefinitely-1.js

@@ -0,0 +1,59 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.until
+description: >
+  NanosecondsToDays can loop arbitrarily long, performing observable operations each iteration.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  15. If sign is 1, then
+    a. Repeat, while days > 0 and intermediateNs > endNs,
+        i. Set days to days - 1.
+        ii. Set intermediateNs to ℝ(? AddZonedDateTime(ℤ(startNs), relativeTo.[[TimeZone]],
+            relativeTo.[[Calendar]], 0, 0, 0, days, 0, 0, 0, 0, 0, 0)).
+  ...
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const dayLengthNs = 86400000000000n;
+const other = new Temporal.ZonedDateTime(dayLengthNs, "UTC", "iso8601");
+
+function createRelativeTo(count) {
+  const tz = new Temporal.TimeZone("UTC");
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, tz, "getPossibleInstantsFor");
+  const cal = new Temporal.Calendar("iso8601");
+  // Return _count_ days for the second call to dateUntil, behaving normally after
+  TemporalHelpers.substituteMethod(cal, "dateUntil", [
+    TemporalHelpers.SUBSTITUTE_SKIP,
+    Temporal.Duration.from({ days: count }),
+  ]);
+  return new Temporal.ZonedDateTime(0n, tz, cal);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+zdt.until(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  200 + 1,
+  "Expected ZonedDateTime.until to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+zdt.until(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  300 + 1,
+  "Expected ZonedDateTime.until to call getPossibleInstantsFor correct number of times"
+);

test/built-ins/Temporal/ZonedDateTime/prototype/until/nanoseconds-to-days-loop-indefinitely-2.js

@@ -0,0 +1,71 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.until
+description: >
+  NanosecondsToDays can loop infinitely.
+info: |
+  NanosecondsToDays ( nanoseconds, relativeTo )
+
+  ...
+  18. Repeat, while done is false,
+    a. Let oneDayFartherNs be ℝ(? AddZonedDateTime(ℤ(intermediateNs), relativeTo.[[TimeZone]],
+       relativeTo.[[Calendar]], 0, 0, 0, sign, 0, 0, 0, 0, 0, 0)).
+    b. Set dayLengthNs to oneDayFartherNs - intermediateNs.
+    c. If (nanoseconds - dayLengthNs) × sign ≥ 0, then
+        i. Set nanoseconds to nanoseconds - dayLengthNs.
+        ii. Set intermediateNs to oneDayFartherNs.
+        iii. Set days to days + sign.
+    d. Else,
+        i. Set done to true.
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const calls = [];
+const dayLengthNs = 86400000000000n;
+const other = new Temporal.ZonedDateTime(dayLengthNs, "UTC", "iso8601");
+
+function createRelativeTo(count) {
+  const dayInstant = new Temporal.Instant(dayLengthNs);
+  const substitutions = [];
+  const timeZone = new Temporal.TimeZone("UTC");
+  // Return constant value for first _count_ calls
+  TemporalHelpers.substituteMethod(
+    timeZone,
+    "getPossibleInstantsFor",
+    substitutions
+  );
+  substitutions.length = count;
+  let i = 0;
+  for (i = 0; i < substitutions.length; i++) {
+    // (this value)
+    substitutions[i] = [dayInstant];
+  }
+  // Record calls in calls[]
+  TemporalHelpers.observeMethod(calls, timeZone, "getPossibleInstantsFor");
+  return new Temporal.ZonedDateTime(0n, timeZone);
+}
+
+let zdt = createRelativeTo(200);
+calls.splice(0); // Reset calls list after ZonedDateTime construction
+zdt.until(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  200 + 1,
+  "Expected ZonedDateTime.until to call getPossibleInstantsFor correct number of times"
+);
+
+zdt = createRelativeTo(300);
+calls.splice(0); // Reset calls list after previous loop + ZonedDateTime construction
+zdt.until(other, {
+  largestUnit: "day",
+});
+assert.sameValue(
+  calls.length,
+  300 + 1,
+  "Expected ZonedDateTime.until to call getPossibleInstantsFor correct number of times"
+);