Add Intl.NumberFormat tests for significant-digit rounding into the next magnitude

harness/testIntl.js

@@ -16,6 +16,7 @@ defines:
   - getLocaleSupportInfo
   - getInvalidLanguageTags
   - isCanonicalizedStructurallyValidLanguageTag
+  - getLocaleBaseName
   - getInvalidLocaleArguments
   - testOption
   - testForUnwantedRegExpChanges
@@ -1813,6 +1814,28 @@ function isCanonicalizedStructurallyValidLanguageTag(locale) {
 }
 
 
+/**
+ * Returns the given language tag without any extension or private use
+ * subtags, like Intl.Locale.prototype.baseName. Use this before appending a
+ * Unicode extension sequence to a locale obtained from resolvedOptions():
+ * some hosts report a default locale that already carries one, such as
+ * "en-US-u-va-posix" under the POSIX locale, and a language tag with two "-u-"
+ * singletons is not structurally valid.
+ * @param {string} locale a canonicalized language tag
+ * @return {string} the language, script, region and variant subtags of locale
+ */
+function getLocaleBaseName(locale) {
+  var subtags = locale.split("-");
+  // Every subtag after the language is at least two characters long, except
+  // for the singletons that introduce extension and private use sequences.
+  for (var i = 1; i < subtags.length; i++) {
+    if (subtags[i].length === 1) {
+      return subtags.slice(0, i).join("-");
+    }
+  }
+  return locale;
+}
+
 /**
  * Returns an array of error cases handled by CanonicalizeLocaleList().
  */
@@ -2387,7 +2410,7 @@ function testNumberFormat(locales, numberingSystems, options, testData) {
   locales.forEach(function (locale) {
     numberingSystems.forEach(function (numbering) {
       var digits = numberingSystemDigits[numbering];
-      var format = new Intl.NumberFormat([locale + "-u-nu-" + numbering], options);
+      var format = new Intl.NumberFormat([getLocaleBaseName(locale) + "-u-nu-" + numbering], options);
 
       function getPatternParts(positive) {
         var n = positive ? 1.1 : -1.1;

test/intl402/Collator/ignore-invalid-unicode-ext-values.js

@@ -7,7 +7,7 @@ description: >
     Tests that Intl.Collator does not accept Unicode locale  extension
     keys and values that are not allowed.
 author: Norbert Lindenberg
-includes: [compareArray.js]
+includes: [compareArray.js, testIntl.js]
 ---*/
 
 var testArray = [
@@ -17,10 +17,10 @@ var testArray = [
         "Å", "Å", "A\u030A"
 ];
 
-var defaultCollator = new Intl.Collator();
+var defaultLocale = getLocaleBaseName(new Intl.Collator().resolvedOptions().locale);
+var defaultCollator = new Intl.Collator([defaultLocale]);
 var defaultOptions = defaultCollator.resolvedOptions();
 var defaultOptionsJSON = JSON.stringify(defaultOptions);
-var defaultLocale = defaultOptions.locale;
 var defaultSortedArray = testArray.slice(0).sort(defaultCollator.compare);
 
 var keyValues = {

test/intl402/Collator/numeric-and-caseFirst.js

@@ -7,6 +7,7 @@ description: >
     Tests that the options numeric and caseFirst can be  set through
     either the locale or the options.
 author: Norbert Lindenberg
+includes: [testIntl.js]
 ---*/
 
 var options = [
@@ -15,7 +16,7 @@ var options = [
 ];
 
 options.forEach(function (option) {
-    var defaultLocale = new Intl.Collator().resolvedOptions().locale;
+    var defaultLocale = getLocaleBaseName(new Intl.Collator().resolvedOptions().locale);
     var collator, opt, result;
 
     // find out which values are supported for a property in the default locale

test/intl402/DateTimeFormat/casing-numbering-system-calendar-options.js

@@ -8,9 +8,10 @@ description: >
     to lower case properly.
 author: Caio Lima
 features: [Array.prototype.includes]
+includes: [testIntl.js]
 ---*/
 
-let defaultLocale = new Intl.DateTimeFormat().resolvedOptions().locale;
+let defaultLocale = getLocaleBaseName(new Intl.DateTimeFormat().resolvedOptions().locale);
 
 let supportedNumberingSystems = ["latn", "arab"].filter(nu =>
   new Intl.DateTimeFormat(defaultLocale + "-u-nu-" + nu)

test/intl402/DateTimeFormat/numbering-system-calendar-options.js

@@ -7,9 +7,10 @@ description: >
     Tests that the options numberingSystem and calendar can be  set through
     either the locale or the options.
 author: Norbert Lindenberg, Daniel Ehrenberg
+includes: [testIntl.js]
 ---*/
 
-let defaultLocale = new Intl.DateTimeFormat().resolvedOptions().locale;
+let defaultLocale = getLocaleBaseName(new Intl.DateTimeFormat().resolvedOptions().locale);
 
 let supportedNumberingSystems = ["latn", "arab"].filter(nu =>
   new Intl.DateTimeFormat(defaultLocale + "-u-nu-" + nu)

test/intl402/DateTimeFormat/prototype/resolvedOptions/resolved-locale-with-hc-unicode.js

@@ -27,9 +27,10 @@ info: |
             a. Let value be optionsValue.
             b. Let supportedExtensionAddition be "".
       ...
+includes: [testIntl.js]
 ---*/
 
-var defaultLocale = new Intl.DateTimeFormat().resolvedOptions().locale;
+var defaultLocale = getLocaleBaseName(new Intl.DateTimeFormat().resolvedOptions().locale);
 var defaultLocaleWithHourCycle = defaultLocale + "-u-hc-h11";
 
 function assertLocale(locale, expectedLocale, options, message) {

test/intl402/NumberFormat/casing-numbering-system-options.js

@@ -7,9 +7,10 @@ description: >
     Tests that the options numberingSystem are mapped to lower case.
 author: Caio Lima
 features: [Array.prototype.includes]
+includes: [testIntl.js]
 ---*/
 
-let defaultLocale = new Intl.NumberFormat().resolvedOptions().locale;
+let defaultLocale = getLocaleBaseName(new Intl.NumberFormat().resolvedOptions().locale);
 
 let supportedNumberingSystems = ["latn", "arab"].filter(nu =>
   new Intl.NumberFormat(defaultLocale + "-u-nu-" + nu)

test/intl402/NumberFormat/numbering-system-options.js

@@ -7,9 +7,10 @@ description: >
     Tests that the options numberingSystem and calendar can be  set through
     either the locale or the options.
 author: Norbert Lindenberg, Daniel Ehrenberg
+includes: [testIntl.js]
 ---*/
 
-let defaultLocale = new Intl.NumberFormat().resolvedOptions().locale;
+let defaultLocale = getLocaleBaseName(new Intl.NumberFormat().resolvedOptions().locale);
 
 let supportedNumberingSystems = ["latn", "arab"].filter(nu =>
   new Intl.NumberFormat(defaultLocale + "-u-nu-" + nu)

test/intl402/NumberFormat/prototype/format/format-significant-digits-rounding-magnitude.js

@@ -0,0 +1,145 @@
+// Copyright (C) 2026 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-torawprecision
+description: >
+  Rounding to significant digits when the rounded value reaches the next order
+  of magnitude
+info: |
+  ToRawPrecision ( x, minPrecision, maxPrecision, unsignedRoundingMode )
+
+  1. Let p be maxPrecision.
+  ...
+  3. Else,
+    a. Let n1 and e1 each be an integer and r1 a mathematical value, with
+       r1 = ToRawPrecisionFn(n1, e1, p), such that r1 ≤ x and r1 is maximized.
+    b. Let n2 and e2 each be an integer and r2 a mathematical value, with
+       r2 = ToRawPrecisionFn(n2, e2, p), such that r2 ≥ x and r2 is minimized.
+    c. Let xFinal be ApplyUnsignedRoundingMode(x, r1, r2, unsignedRoundingMode).
+    d. If xFinal is r1, then
+      i. Let n be n1.
+      ii. Let e be e1.
+    e. Else,
+      i. Let n be n2.
+      ii. Let e be e2.
+    f. Let m be the String consisting of the digits of the decimal
+       representation of n (in order, with no leading zeroes).
+  4. If e ≥ (p - 1), then
+    a. Set m to the string-concatenation of m and e - p + 1 occurrences of the
+       code unit 0x0030 (DIGIT ZERO).
+    b. Let int be e + 1.
+  5. Else if e ≥ 0, then
+    a. Set m to the string-concatenation of the first e + 1 code units of m,
+       the code unit 0x002E (FULL STOP), and the remaining p - (e + 1) code
+       units of m.
+    b. Let int be e + 1.
+  6. Else,
+    a. Assert: e < 0.
+    b. Set m to the string-concatenation of "0.", -(e + 1) occurrences of the
+       code unit 0x0030 (DIGIT ZERO), and m.
+    c. Let int be 1.
+  7. If m contains the code unit 0x002E (FULL STOP) and
+     maxPrecision > minPrecision, then
+    a. Let cut be maxPrecision - minPrecision.
+    b. Repeat, while cut > 0 and the last code unit of m is 0x0030
+       (DIGIT ZERO),
+      i. Remove the last code unit from m.
+      ii. Set cut to cut - 1.
+    c. If the last code unit of m is 0x002E (FULL STOP), then
+      i. Remove the last code unit from m.
+includes: [testIntl.js]
+---*/
+
+var locales = [
+  new Intl.NumberFormat().resolvedOptions().locale,
+  "ar", "de", "th", "ja"
+];
+var numberingSystems = ["latn", "arab", "thai", "hanidec"];
+
+// minimumSignificantDigits = maximumSignificantDigits, so no trailing zeros
+// are trimmed and the digit count of the result is visible directly.
+testNumberFormat(locales, numberingSystems,
+  { useGrouping: false, minimumSignificantDigits: 3, maximumSignificantDigits: 3 },
+  {
+    // step 6: e = -3 → e = -2 (still e < 0)
+    "0.0009999": "0.00100",
+    "-0.0009999": "-0.00100",
+    // step 6: e = -2 → e = -1
+    "0.09999": "0.100",
+    "-0.09999": "-0.100",
+    // step 6 (e = -1) → step 5 (e = 0)
+    "0.9999": "1.00",
+    "-0.9999": "-1.00",
+    // step 5: e = 0 → e = 1
+    "9.999": "10.0",
+    "-9.999": "-10.0",
+    // step 5 (e = 1) → step 4 (e = 2 = p - 1)
+    "99.99": "100",
+    "-99.99": "-100",
+    // step 4: e = 2 → e = 3
+    "999.9": "1000",
+    "-999.9": "-1000",
+    // step 4: e = 5 → e = 6
+    "999999.9": "1000000",
+    "-999999.9": "-1000000",
+    // control values that round without changing magnitude
+    "9.994": "9.99",
+    "99.94": "99.9",
+    "0.9994": "0.999",
+  });
+
+// Default minimumSignificantDigits of 1: rollover still happens, and the
+// zeros that appear after the FULL STOP are trimmed by step 7.
+testNumberFormat(locales, numberingSystems,
+  { useGrouping: false, maximumSignificantDigits: 3 },
+  {
+    "0.0009999": "0.001",
+    "0.09999": "0.1",
+    "0.9999": "1",
+    "-0.9999": "-1",
+    "9.999": "10",
+    "-9.999": "-10",
+    "99.99": "100",
+    "-99.99": "-100",
+    "999.9": "1000",
+    "999999.9": "1000000",
+  });
+
+// Lower minimum: step 7 trims at most maxPrecision - minPrecision zeros.
+testNumberFormat(locales, numberingSystems,
+  { useGrouping: false, minimumSignificantDigits: 2, maximumSignificantDigits: 3 },
+  {
+    "0.9999": "1.0",
+    "9.999": "10",
+    "99.99": "100",
+  });
+
+// Two significant digits
+testNumberFormat(locales, numberingSystems,
+  { useGrouping: false, minimumSignificantDigits: 2, maximumSignificantDigits: 2 },
+  {
+    "0.996": "1.0",
+    "9.96": "10",
+    "99.6": "100",
+    "996": "1000",
+  });
+
+// Larger precision
+testNumberFormat(locales, numberingSystems,
+  { useGrouping: false, minimumSignificantDigits: 5, maximumSignificantDigits: 5 },
+  {
+    "9.99996": "10.000",
+    "99999.6": "100000",
+    "0.999996": "1.0000",
+  });
+
+// The rounded value is always compared against x; a value just below the
+// rounding boundary must not roll over.
+testNumberFormat(locales, numberingSystems,
+  { useGrouping: false, minimumSignificantDigits: 3, maximumSignificantDigits: 3 },
+  {
+    "9.9949": "9.99",
+    "99.949": "99.9",
+    "999.49": "999",
+  });