Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3731 insertions, 0 deletions

diff --git a/js/src/builtin/intl/make_intl_data.py b/js/src/builtin/intl/make_intl_data.py
new file mode 100755
index 0000000000..802902336e
--- /dev/null
+++ b/js/src/builtin/intl/make_intl_data.py
@@ -0,0 +1,3731 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+""" Usage:
+    make_intl_data.py langtags [cldr_core.zip]
+    make_intl_data.py tzdata
+    make_intl_data.py currency
+    make_intl_data.py units
+    make_intl_data.py numbering
+
+
+    Target "langtags":
+    This script extracts information about 1) mappings between deprecated and
+    current Unicode BCP 47 locale identifiers, and 2) deprecated and current
+    BCP 47 Unicode extension value from CLDR, and converts it to C++ mapping
+    code in LanguageTagGenerated.cpp. The code is used in LanguageTag.cpp.
+
+
+    Target "tzdata":
+    This script computes which time zone informations are not up-to-date in ICU
+    and provides the necessary mappings to workaround this problem.
+    https://ssl.icu-project.org/trac/ticket/12044
+
+
+    Target "currency":
+    Generates the mapping from currency codes to decimal digits used for them.
+
+
+    Target "units":
+    Generate source and test files using the list of so-called "sanctioned unit
+    identifiers" and verifies that the ICU data filter includes these units.
+
+
+    Target "numbering":
+    Generate source and test files using the list of numbering systems with
+    simple digit mappings and verifies that it's in sync with ICU/CLDR.
+"""
+
+from __future__ import print_function
+import os
+import re
+import io
+import json
+import sys
+import tarfile
+import tempfile
+import yaml
+from contextlib import closing
+from functools import partial, total_ordering
+from itertools import chain, groupby, tee
+from operator import attrgetter, itemgetter
+from zipfile import ZipFile
+
+if sys.version_info.major == 2:
+    from itertools import (
+        ifilter as filter,
+        ifilterfalse as filterfalse,
+        imap as map,
+        izip_longest as zip_longest,
+    )
+    from urllib2 import urlopen, Request as UrlRequest
+    from urlparse import urlsplit
+else:
+    from itertools import filterfalse, zip_longest
+    from urllib.request import urlopen, Request as UrlRequest
+    from urllib.parse import urlsplit
+
+
+# From https://docs.python.org/3/library/itertools.html
+def grouper(iterable, n, fillvalue=None):
+    "Collect data into fixed-length chunks or blocks"
+    # grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx"
+    args = [iter(iterable)] * n
+    return zip_longest(*args, fillvalue=fillvalue)
+
+
+def writeMappingHeader(println, description, source, url):
+    if type(description) is not list:
+        description = [description]
+    for desc in description:
+        println("// {0}".format(desc))
+    println("// Derived from {0}.".format(source))
+    println("// {0}".format(url))
+
+
+def writeMappingsVar(println, mapping, name, description, source, url):
+    """Writes a variable definition with a mapping table.
+
+    Writes the contents of dictionary |mapping| through the |println|
+    function with the given variable name and a comment with description,
+    fileDate, and URL.
+    """
+    println("")
+    writeMappingHeader(println, description, source, url)
+    println("var {0} = {{".format(name))
+    for (key, value) in sorted(mapping.items(), key=itemgetter(0)):
+        println('    "{0}": "{1}",'.format(key, value))
+    println("};")
+
+
+def writeMappingsBinarySearch(
+    println,
+    fn_name,
+    type_name,
+    name,
+    validate_fn,
+    validate_case_fn,
+    mappings,
+    tag_maxlength,
+    description,
+    source,
+    url,
+):
+    """Emit code to perform a binary search on language tag subtags.
+
+    Uses the contents of |mapping|, which can either be a dictionary or set,
+    to emit a mapping function to find subtag replacements.
+    """
+    println("")
+    writeMappingHeader(println, description, source, url)
+    println(
+        """
+bool js::intl::LanguageTag::{0}({1} {2}) {{
+  MOZ_ASSERT({3}({2}.span()));
+  MOZ_ASSERT({4}({2}.span()));
+""".format(
+            fn_name, type_name, name, validate_fn, validate_case_fn
+        ).strip()
+    )
+
+    def write_array(subtags, name, length, fixed):
+        if fixed:
+            println(
+                "    static const char {}[{}][{}] = {{".format(
+                    name, len(subtags), length + 1
+                )
+            )
+        else:
+            println("    static const char* {}[{}] = {{".format(name, len(subtags)))
+
+        # Group in pairs of ten to not exceed the 80 line column limit.
+        for entries in grouper(subtags, 10):
+            entries = (
+                '"{}"'.format(tag).rjust(length + 2)
+                for tag in entries
+                if tag is not None
+            )
+            println("      {},".format(", ".join(entries)))
+
+        println("    };")
+
+    trailing_return = True
+
+    # Sort the subtags by length. That enables using an optimized comparator
+    # for the binary search, which only performs a single |memcmp| for multiple
+    # of two subtag lengths.
+    mappings_keys = mappings.keys() if type(mappings) == dict else mappings
+    for (length, subtags) in groupby(sorted(mappings_keys, key=len), len):
+        # Omit the length check if the current length is the maximum length.
+        if length != tag_maxlength:
+            println(
+                """
+  if ({}.length() == {}) {{
+""".format(
+                    name, length
+                ).rstrip(
+                    "\n"
+                )
+            )
+        else:
+            trailing_return = False
+            println(
+                """
+  {
+""".rstrip(
+                    "\n"
+                )
+            )
+
+        # The subtags need to be sorted for binary search to work.
+        subtags = sorted(subtags)
+
+        def equals(subtag):
+            return """{}.equalTo("{}")""".format(name, subtag)
+
+        # Don't emit a binary search for short lists.
+        if len(subtags) == 1:
+            if type(mappings) == dict:
+                println(
+                    """
+    if ({}) {{
+      {}.set("{}");
+      return true;
+    }}
+    return false;
+""".format(
+                        equals(subtags[0]), name, mappings[subtags[0]]
+                    ).strip(
+                        "\n"
+                    )
+                )
+            else:
+                println(
+                    """
+    return {};
+""".format(
+                        equals(subtags[0])
+                    ).strip(
+                        "\n"
+                    )
+                )
+        elif len(subtags) <= 4:
+            if type(mappings) == dict:
+                for subtag in subtags:
+                    println(
+                        """
+    if ({}) {{
+      {}.set("{}");
+      return true;
+    }}
+""".format(
+                            equals(subtag), name, mappings[subtag]
+                        ).strip(
+                            "\n"
+                        )
+                    )
+
+                println(
+                    """
+    return false;
+""".strip(
+                        "\n"
+                    )
+                )
+            else:
+                cond = (equals(subtag) for subtag in subtags)
+                cond = (" ||\n" + " " * (4 + len("return "))).join(cond)
+                println(
+                    """
+    return {};
+""".format(
+                        cond
+                    ).strip(
+                        "\n"
+                    )
+                )
+        else:
+            write_array(subtags, name + "s", length, True)
+
+            if type(mappings) == dict:
+                write_array([mappings[k] for k in subtags], "aliases", length, False)
+
+                println(
+                    """
+    if (const char* replacement = SearchReplacement({0}s, aliases, {0})) {{
+      {0}.set(mozilla::MakeStringSpan(replacement));
+      return true;
+    }}
+    return false;
+""".format(
+                        name
+                    ).rstrip()
+                )
+            else:
+                println(
+                    """
+    return HasReplacement({0}s, {0});
+""".format(
+                        name
+                    ).rstrip()
+                )
+
+        println(
+            """
+  }
+""".strip(
+                "\n"
+            )
+        )
+
+    if trailing_return:
+        println(
+            """
+  return false;"""
+        )
+
+    println(
+        """
+}""".lstrip(
+            "\n"
+        )
+    )
+
+
+def writeComplexLanguageTagMappings(
+    println, complex_language_mappings, description, source, url
+):
+    println("")
+    writeMappingHeader(println, description, source, url)
+    println(
+        """
+void js::intl::LanguageTag::performComplexLanguageMappings() {
+  MOZ_ASSERT(IsStructurallyValidLanguageTag(language().span()));
+  MOZ_ASSERT(IsCanonicallyCasedLanguageTag(language().span()));
+""".lstrip()
+    )
+
+    # Merge duplicate language entries.
+    language_aliases = {}
+    for (deprecated_language, (language, script, region)) in sorted(
+        complex_language_mappings.items(), key=itemgetter(0)
+    ):
+        key = (language, script, region)
+        if key not in language_aliases:
+            language_aliases[key] = []
+        else:
+            language_aliases[key].append(deprecated_language)
+
+    first_language = True
+    for (deprecated_language, (language, script, region)) in sorted(
+        complex_language_mappings.items(), key=itemgetter(0)
+    ):
+        key = (language, script, region)
+        if deprecated_language in language_aliases[key]:
+            continue
+
+        if_kind = "if" if first_language else "else if"
+        first_language = False
+
+        cond = (
+            'language().equalTo("{}")'.format(lang)
+            for lang in [deprecated_language] + language_aliases[key]
+        )
+        cond = (" ||\n" + " " * (2 + len(if_kind) + 2)).join(cond)
+
+        println(
+            """
+  {} ({}) {{""".format(
+                if_kind, cond
+            ).strip(
+                "\n"
+            )
+        )
+
+        println(
+            """
+    setLanguage("{}");""".format(
+                language
+            ).strip(
+                "\n"
+            )
+        )
+
+        if script is not None:
+            println(
+                """
+    if (script().missing()) {{
+      setScript("{}");
+    }}""".format(
+                    script
+                ).strip(
+                    "\n"
+                )
+            )
+        if region is not None:
+            println(
+                """
+    if (region().missing()) {{
+      setRegion("{}");
+    }}""".format(
+                    region
+                ).strip(
+                    "\n"
+                )
+            )
+        println(
+            """
+  }""".strip(
+                "\n"
+            )
+        )
+
+    println(
+        """
+}
+""".strip(
+            "\n"
+        )
+    )
+
+
+def writeComplexRegionTagMappings(
+    println, complex_region_mappings, description, source, url
+):
+    println("")
+    writeMappingHeader(println, description, source, url)
+    println(
+        """
+void js::intl::LanguageTag::performComplexRegionMappings() {
+  MOZ_ASSERT(IsStructurallyValidLanguageTag(language().span()));
+  MOZ_ASSERT(IsCanonicallyCasedLanguageTag(language().span()));
+  MOZ_ASSERT(IsStructurallyValidRegionTag(region().span()));
+  MOZ_ASSERT(IsCanonicallyCasedRegionTag(region().span()));
+""".lstrip()
+    )
+
+    # |non_default_replacements| is a list and hence not hashable. Convert it
+    # to a string to get a proper hashable value.
+    def hash_key(default, non_default_replacements):
+        return (default, str(sorted(str(v) for v in non_default_replacements)))
+
+    # Merge duplicate region entries.
+    region_aliases = {}
+    for (deprecated_region, (default, non_default_replacements)) in sorted(
+        complex_region_mappings.items(), key=itemgetter(0)
+    ):
+        key = hash_key(default, non_default_replacements)
+        if key not in region_aliases:
+            region_aliases[key] = []
+        else:
+            region_aliases[key].append(deprecated_region)
+
+    first_region = True
+    for (deprecated_region, (default, non_default_replacements)) in sorted(
+        complex_region_mappings.items(), key=itemgetter(0)
+    ):
+        key = hash_key(default, non_default_replacements)
+        if deprecated_region in region_aliases[key]:
+            continue
+
+        if_kind = "if" if first_region else "else if"
+        first_region = False
+
+        cond = (
+            'region().equalTo("{}")'.format(region)
+            for region in [deprecated_region] + region_aliases[key]
+        )
+        cond = (" ||\n" + " " * (2 + len(if_kind) + 2)).join(cond)
+
+        println(
+            """
+  {} ({}) {{""".format(
+                if_kind, cond
+            ).strip(
+                "\n"
+            )
+        )
+
+        replacement_regions = sorted(
+            {region for (_, _, region) in non_default_replacements}
+        )
+
+        first_case = True
+        for replacement_region in replacement_regions:
+            replacement_language_script = sorted(
+                (language, script)
+                for (language, script, region) in (non_default_replacements)
+                if region == replacement_region
+            )
+
+            if_kind = "if" if first_case else "else if"
+            first_case = False
+
+            def compare_tags(language, script):
+                if script is None:
+                    return 'language().equalTo("{}")'.format(language)
+                return '(language().equalTo("{}") && script().equalTo("{}"))'.format(
+                    language, script
+                )
+
+            cond = (
+                compare_tags(language, script)
+                for (language, script) in replacement_language_script
+            )
+            cond = (" ||\n" + " " * (4 + len(if_kind) + 2)).join(cond)
+
+            println(
+                """
+    {} ({}) {{
+      setRegion("{}");
+    }}""".format(
+                    if_kind, cond, replacement_region
+                )
+                .rstrip()
+                .strip("\n")
+            )
+
+        println(
+            """
+    else {{
+      setRegion("{}");
+    }}
+  }}""".format(
+                default
+            )
+            .rstrip()
+            .strip("\n")
+        )
+
+    println(
+        """
+}
+""".strip(
+            "\n"
+        )
+    )
+
+
+def writeVariantTagMappings(println, variant_mappings, description, source, url):
+    """ Writes a function definition that maps variant subtags. """
+    println(
+        """
+static const char* ToCharPointer(const char* str) {
+  return str;
+}
+
+static const char* ToCharPointer(const js::UniqueChars& str) {
+  return str.get();
+}
+
+template <typename T, typename U = T>
+static bool IsLessThan(const T& a, const U& b) {
+  return strcmp(ToCharPointer(a), ToCharPointer(b)) < 0;
+}
+"""
+    )
+    writeMappingHeader(println, description, source, url)
+    println(
+        """
+bool js::intl::LanguageTag::performVariantMappings(JSContext* cx) {
+  // The variant subtags need to be sorted for binary search.
+  MOZ_ASSERT(std::is_sorted(variants_.begin(), variants_.end(),
+                            IsLessThan<decltype(variants_)::ElementType>));
+
+  auto insertVariantSortedIfNotPresent = [&](const char* variant) {
+    auto* p = std::lower_bound(variants_.begin(), variants_.end(), variant,
+                               IsLessThan<decltype(variants_)::ElementType,
+                                          decltype(variant)>);
+
+    // Don't insert the replacement when already present.
+    if (p != variants_.end() && strcmp(p->get(), variant) == 0) {
+      return true;
+    }
+
+    // Insert the preferred variant in sort order.
+    auto preferred = DuplicateString(cx, variant);
+    if (!preferred) {
+      return false;
+    }
+    return !!variants_.insert(p, std::move(preferred));
+  };
+
+  for (size_t i = 0; i < variants_.length(); ) {
+    auto& variant = variants_[i];
+    MOZ_ASSERT(IsCanonicallyCasedVariantTag(mozilla::MakeStringSpan(variant.get())));
+""".lstrip()
+    )
+
+    first_variant = True
+
+    for (deprecated_variant, (type, replacement)) in sorted(
+        variant_mappings.items(), key=itemgetter(0)
+    ):
+        if_kind = "if" if first_variant else "else if"
+        first_variant = False
+
+        println(
+            """
+    {} (strcmp(variant.get(), "{}") == 0) {{
+      variants_.erase(variants_.begin() + i);
+""".format(
+                if_kind, deprecated_variant
+            ).strip(
+                "\n"
+            )
+        )
+
+        if type == "language":
+            println(
+                """
+      setLanguage("{}");
+""".format(
+                    replacement
+                ).strip(
+                    "\n"
+                )
+            )
+        elif type == "region":
+            println(
+                """
+      setRegion("{}");
+""".format(
+                    replacement
+                ).strip(
+                    "\n"
+                )
+            )
+        else:
+            assert type == "variant"
+            println(
+                """
+      if (!insertVariantSortedIfNotPresent("{}")) {{
+        return false;
+      }}
+""".format(
+                    replacement
+                ).strip(
+                    "\n"
+                )
+            )
+
+        println(
+            """
+    }
+""".strip(
+                "\n"
+            )
+        )
+
+    println(
+        """
+    else {
+      i++;
+    }
+  }
+  return true;
+}
+""".strip(
+            "\n"
+        )
+    )
+
+
+def writeGrandfatheredMappingsFunction(
+    println, grandfathered_mappings, description, source, url
+):
+    """ Writes a function definition that maps grandfathered language tags. """
+    println("")
+    writeMappingHeader(println, description, source, url)
+    println(
+        """\
+bool js::intl::LanguageTag::updateGrandfatheredMappings(JSContext* cx) {
+  // We're mapping regular grandfathered tags to non-grandfathered form here.
+  // Other tags remain unchanged.
+  //
+  // regular       = "art-lojban"
+  //               / "cel-gaulish"
+  //               / "no-bok"
+  //               / "no-nyn"
+  //               / "zh-guoyu"
+  //               / "zh-hakka"
+  //               / "zh-min"
+  //               / "zh-min-nan"
+  //               / "zh-xiang"
+  //
+  // Therefore we can quickly exclude most tags by checking every
+  // |unicode_locale_id| subcomponent for characteristics not shared by any of
+  // the regular grandfathered (RG) tags:
+  //
+  //   * Real-world |unicode_language_subtag|s are all two or three letters,
+  //     so don't waste time running a useless |language.length > 3| fast-path.
+  //   * No RG tag has a "script"-looking component.
+  //   * No RG tag has a "region"-looking component.
+  //   * The RG tags that match |unicode_locale_id| (art-lojban, cel-gaulish,
+  //     zh-guoyu, zh-hakka, zh-xiang) have exactly one "variant". (no-bok,
+  //     no-nyn, zh-min, and zh-min-nan require BCP47's extlang subtag
+  //     that |unicode_locale_id| doesn't support.)
+  //   * No RG tag contains |extensions| or |pu_extensions|.
+  if (script().present() ||
+      region().present() ||
+      variants().length() != 1 ||
+      extensions().length() != 0 ||
+      privateuse()) {
+    return true;
+  }
+
+  MOZ_ASSERT(IsCanonicallyCasedLanguageTag(language().span()));
+  MOZ_ASSERT(IsCanonicallyCasedVariantTag(mozilla::MakeStringSpan(variants()[0].get())));
+
+  auto variantEqualTo = [this](const char* variant) {
+    return strcmp(variants()[0].get(), variant) == 0;
+  };"""
+    )
+
+    # From Unicode BCP 47 locale identifier <https://unicode.org/reports/tr35/>.
+    #
+    # Doesn't allow any 'extensions' subtags.
+    re_unicode_locale_id = re.compile(
+        r"""
+        ^
+        # unicode_language_id = unicode_language_subtag
+        #     unicode_language_subtag = alpha{2,3} | alpha{5,8}
+        (?P<language>[a-z]{2,3}|[a-z]{5,8})
+
+        # (sep unicode_script_subtag)?
+        #     unicode_script_subtag = alpha{4}
+        (?:-(?P<script>[a-z]{4}))?
+
+        # (sep unicode_region_subtag)?
+        #     unicode_region_subtag = (alpha{2} | digit{3})
+        (?:-(?P<region>([a-z]{2}|[0-9]{3})))?
+
+        # (sep unicode_variant_subtag)*
+        #     unicode_variant_subtag = (alphanum{5,8} | digit alphanum{3})
+        (?P<variants>(-([a-z0-9]{5,8}|[0-9][a-z0-9]{3}))+)?
+
+        # pu_extensions?
+        #     pu_extensions = sep [xX] (sep alphanum{1,8})+
+        (?:-(?P<privateuse>x(-[a-z0-9]{1,8})+))?
+        $
+        """,
+        re.IGNORECASE | re.VERBOSE,
+    )
+
+    is_first = True
+
+    for (tag, modern) in sorted(grandfathered_mappings.items(), key=itemgetter(0)):
+        tag_match = re_unicode_locale_id.match(tag)
+        assert tag_match is not None
+
+        tag_language = tag_match.group("language")
+        assert (
+            tag_match.group("script") is None
+        ), "{} does not contain a script subtag".format(tag)
+        assert (
+            tag_match.group("region") is None
+        ), "{} does not contain a region subtag".format(tag)
+        tag_variants = tag_match.group("variants")
+        assert tag_variants is not None, "{} contains a variant subtag".format(tag)
+        assert (
+            tag_match.group("privateuse") is None
+        ), "{} does not contain a privateuse subtag".format(tag)
+
+        tag_variant = tag_variants[1:]
+        assert "-" not in tag_variant, "{} contains only a single variant".format(tag)
+
+        modern_match = re_unicode_locale_id.match(modern)
+        assert modern_match is not None
+
+        modern_language = modern_match.group("language")
+        modern_script = modern_match.group("script")
+        modern_region = modern_match.group("region")
+        modern_variants = modern_match.group("variants")
+        modern_privateuse = modern_match.group("privateuse")
+
+        println(
+            """
+  // {} -> {}
+""".format(
+                tag, modern
+            ).rstrip()
+        )
+
+        println(
+            """
+  {}if (language().equalTo("{}") && variantEqualTo("{}")) {{
+        """.format(
+                "" if is_first else "else ", tag_language, tag_variant
+            )
+            .rstrip()
+            .strip("\n")
+        )
+
+        is_first = False
+
+        println(
+            """
+    setLanguage("{}");
+        """.format(
+                modern_language
+            )
+            .rstrip()
+            .strip("\n")
+        )
+
+        if modern_script is not None:
+            println(
+                """
+    setScript("{}");
+            """.format(
+                    modern_script
+                )
+                .rstrip()
+                .strip("\n")
+            )
+
+        if modern_region is not None:
+            println(
+                """
+    setRegion("{}");
+            """.format(
+                    modern_region
+                )
+                .rstrip()
+                .strip("\n")
+            )
+
+        assert (
+            modern_variants is None
+        ), "all regular grandfathered tags' modern forms do not contain variant subtags"
+
+        println(
+            """
+    clearVariants();
+        """.rstrip().strip(
+                "\n"
+            )
+        )
+
+        if modern_privateuse is not None:
+            println(
+                """
+    auto privateuse = DuplicateString(cx, "{}");
+    if (!privateuse) {{
+      return false;
+    }}
+    setPrivateuse(std::move(privateuse));
+        """.format(
+                    modern_privateuse
+                )
+                .rstrip()
+                .rstrip("\n")
+            )
+
+        println(
+            """
+    return true;
+  }""".rstrip().strip(
+                "\n"
+            )
+        )
+
+    println(
+        """
+  return true;
+}"""
+    )
+
+
+def readSupplementalData(core_file):
+    """Reads CLDR Supplemental Data and extracts information for Intl.js.
+
+    Information extracted:
+    - grandfatheredMappings: mappings from grandfathered tags to preferred
+      complete language tags
+    - languageMappings: mappings from language subtags to preferred subtags
+    - complexLanguageMappings: mappings from language subtags with complex rules
+    - regionMappings: mappings from region subtags to preferred subtags
+    - complexRegionMappings: mappings from region subtags with complex rules
+    - variantMappings: mappings from variant subtags to preferred subtags
+    - likelySubtags: likely subtags used for generating test data only
+    Returns these mappings as dictionaries.
+    """
+    import xml.etree.ElementTree as ET
+
+    # From Unicode BCP 47 locale identifier <https://unicode.org/reports/tr35/>.
+    re_unicode_language_id = re.compile(
+        r"""
+        ^
+        # unicode_language_id = unicode_language_subtag
+        #     unicode_language_subtag = alpha{2,3} | alpha{5,8}
+        (?P<language>[a-z]{2,3}|[a-z]{5,8})
+
+        # (sep unicode_script_subtag)?
+        #     unicode_script_subtag = alpha{4}
+        (?:-(?P<script>[a-z]{4}))?
+
+        # (sep unicode_region_subtag)?
+        #     unicode_region_subtag = (alpha{2} | digit{3})
+        (?:-(?P<region>([a-z]{2}|[0-9]{3})))?
+
+        # (sep unicode_variant_subtag)*
+        #     unicode_variant_subtag = (alphanum{5,8} | digit alphanum{3})
+        (?P<variants>(-([a-z0-9]{5,8}|[0-9][a-z0-9]{3}))+)?
+        $
+        """,
+        re.IGNORECASE | re.VERBOSE,
+    )
+
+    re_unicode_language_subtag = re.compile(
+        r"""
+        ^
+        # unicode_language_subtag = alpha{2,3} | alpha{5,8}
+        ([a-z]{2,3}|[a-z]{5,8})
+        $
+        """,
+        re.IGNORECASE | re.VERBOSE,
+    )
+
+    re_unicode_region_subtag = re.compile(
+        r"""
+        ^
+        # unicode_region_subtag = (alpha{2} | digit{3})
+        ([a-z]{2}|[0-9]{3})
+        $
+        """,
+        re.IGNORECASE | re.VERBOSE,
+    )
+
+    re_unicode_variant_subtag = re.compile(
+        r"""
+        ^
+        # unicode_variant_subtag = (alphanum{5,8} | digit alphanum{3})
+        ([a-z0-9]{5,8}|(?:[0-9][a-z0-9]{3}))
+        $
+        """,
+        re.IGNORECASE | re.VERBOSE,
+    )
+
+    # The fixed list of BCP 47 grandfathered language tags.
+    grandfathered_tags = (
+        "art-lojban",
+        "cel-gaulish",
+        "en-GB-oed",
+        "i-ami",
+        "i-bnn",
+        "i-default",
+        "i-enochian",
+        "i-hak",
+        "i-klingon",
+        "i-lux",
+        "i-mingo",
+        "i-navajo",
+        "i-pwn",
+        "i-tao",
+        "i-tay",
+        "i-tsu",
+        "no-bok",
+        "no-nyn",
+        "sgn-BE-FR",
+        "sgn-BE-NL",
+        "sgn-CH-DE",
+        "zh-guoyu",
+        "zh-hakka",
+        "zh-min",
+        "zh-min-nan",
+        "zh-xiang",
+    )
+
+    # The list of grandfathered tags which are valid Unicode BCP 47 locale identifiers.
+    unicode_bcp47_grandfathered_tags = {
+        tag for tag in grandfathered_tags if re_unicode_language_id.match(tag)
+    }
+
+    # Dictionary of simple language subtag mappings, e.g. "in" -> "id".
+    language_mappings = {}
+
+    # Dictionary of complex language subtag mappings, modifying more than one
+    # subtag, e.g. "sh" -> ("sr", "Latn", None) and "cnr" -> ("sr", None, "ME").
+    complex_language_mappings = {}
+
+    # Dictionary of simple region subtag mappings, e.g. "DD" -> "DE".
+    region_mappings = {}
+
+    # Dictionary of complex region subtag mappings, containing more than one
+    # replacement, e.g. "SU" -> ("RU", ["AM", "AZ", "BY", ...]).
+    complex_region_mappings = {}
+
+    # Dictionary of aliased variant subtags to a tuple of preferred replacement
+    # type and replacement, e.g. "arevela" -> ("language", "hy") or
+    # "aaland" -> ("region", "AX") or "heploc" -> ("variant", "alalc97").
+    variant_mappings = {}
+
+    # Dictionary of grandfathered mappings to preferred values.
+    grandfathered_mappings = {}
+
+    # CLDR uses "_" as the separator for some elements. Replace it with "-".
+    def bcp47_id(cldr_id):
+        return cldr_id.replace("_", "-")
+
+    # CLDR uses the canonical case for most entries, but there are some
+    # exceptions, like:
+    #   <languageAlias type="drw" replacement="fa_af" reason="deprecated"/>
+    # Therefore canonicalize all tags to be on the safe side.
+    def bcp47_canonical(language, script, region):
+        # Canonical case for language subtags is lower case.
+        # Canonical case for script subtags is title case.
+        # Canonical case for region subtags is upper case.
+        return (
+            language.lower() if language else None,
+            script.title() if script else None,
+            region.upper() if region else None,
+        )
+
+    tree = ET.parse(core_file.open("common/supplemental/supplementalMetadata.xml"))
+
+    for language_alias in tree.iterfind(".//languageAlias"):
+        type = bcp47_id(language_alias.get("type"))
+        replacement = bcp47_id(language_alias.get("replacement"))
+
+        # Handle grandfathered mappings first.
+        if type in unicode_bcp47_grandfathered_tags:
+            grandfathered_mappings[type] = replacement
+            continue
+
+        # We're only interested in language subtag matches, so ignore any
+        # entries which have additional subtags.
+        if re_unicode_language_subtag.match(type) is None:
+            continue
+
+        assert type.islower()
+
+        if re_unicode_language_subtag.match(replacement) is not None:
+            # Canonical case for language subtags is lower-case.
+            language_mappings[type] = replacement.lower()
+        else:
+            replacement_match = re_unicode_language_id.match(replacement)
+            assert (
+                replacement_match is not None
+            ), "{} invalid Unicode BCP 47 locale identifier".format(replacement)
+            assert (
+                replacement_match.group("variants") is None
+            ), "{}: unexpected variant subtags in {}".format(type, replacement)
+
+            complex_language_mappings[type] = bcp47_canonical(
+                replacement_match.group("language"),
+                replacement_match.group("script"),
+                replacement_match.group("region"),
+            )
+
+    for territory_alias in tree.iterfind(".//territoryAlias"):
+        type = territory_alias.get("type")
+        replacement = territory_alias.get("replacement")
+
+        # We're only interested in region subtag matches, so ignore any entries
+        # which contain legacy formats, e.g. three letter region codes.
+        if re_unicode_region_subtag.match(type) is None:
+            continue
+
+        assert type.isupper() or type.isdigit()
+
+        if re_unicode_region_subtag.match(replacement) is not None:
+            # Canonical case for region subtags is upper-case.
+            region_mappings[type] = replacement.upper()
+        else:
+            # Canonical case for region subtags is upper-case.
+            replacements = [r.upper() for r in replacement.split(" ")]
+            assert all(
+                re_unicode_region_subtag.match(loc) is not None for loc in replacements
+            ), "{} invalid region subtags".format(replacement)
+            complex_region_mappings[type] = replacements
+
+    for variant_alias in tree.iterfind(".//variantAlias"):
+        type = variant_alias.get("type")
+        replacement = variant_alias.get("replacement")
+
+        assert (
+            re_unicode_variant_subtag.match(type) is not None
+        ), "{} invalid variant subtag".format(type)
+
+        # Normalize the case, because some variants are in upper case.
+        type = type.lower()
+
+        # The replacement can be a language, a region, or a variant subtag.
+        # Language and region subtags are case normalized, variant subtags can
+        # be in any case.
+
+        if (
+            re_unicode_language_subtag.match(replacement) is not None
+            and replacement.islower()
+        ):
+            variant_mappings[type] = ("language", replacement)
+
+        elif re_unicode_region_subtag.match(replacement) is not None:
+            assert (
+                replacement.isupper() or replacement.isdigit()
+            ), "{} invalid variant subtag replacement".format(replacement)
+            variant_mappings[type] = ("region", replacement)
+
+        else:
+            assert (
+                re_unicode_variant_subtag.match(replacement) is not None
+            ), "{} invalid variant subtag replacement".format(replacement)
+            variant_mappings[type] = ("variant", replacement.lower())
+
+    tree = ET.parse(core_file.open("common/supplemental/likelySubtags.xml"))
+
+    likely_subtags = {}
+
+    for likely_subtag in tree.iterfind(".//likelySubtag"):
+        from_tag = bcp47_id(likely_subtag.get("from"))
+        from_match = re_unicode_language_id.match(from_tag)
+        assert (
+            from_match is not None
+        ), "{} invalid Unicode BCP 47 locale identifier".format(from_tag)
+        assert (
+            from_match.group("variants") is None
+        ), "unexpected variant subtags in {}".format(from_tag)
+
+        to_tag = bcp47_id(likely_subtag.get("to"))
+        to_match = re_unicode_language_id.match(to_tag)
+        assert (
+            to_match is not None
+        ), "{} invalid Unicode BCP 47 locale identifier".format(to_tag)
+        assert (
+            to_match.group("variants") is None
+        ), "unexpected variant subtags in {}".format(to_tag)
+
+        from_canonical = bcp47_canonical(
+            from_match.group("language"),
+            from_match.group("script"),
+            from_match.group("region"),
+        )
+
+        to_canonical = bcp47_canonical(
+            to_match.group("language"),
+            to_match.group("script"),
+            to_match.group("region"),
+        )
+
+        likely_subtags[from_canonical] = to_canonical
+
+    complex_region_mappings_final = {}
+
+    for (deprecated_region, replacements) in complex_region_mappings.items():
+        # Find all likely subtag entries which don't already contain a region
+        # subtag and whose target region is in the list of replacement regions.
+        region_likely_subtags = [
+            (from_language, from_script, to_region)
+            for (
+                (from_language, from_script, from_region),
+                (_, _, to_region),
+            ) in likely_subtags.items()
+            if from_region is None and to_region in replacements
+        ]
+
+        # The first replacement entry is the default region.
+        default = replacements[0]
+
+        # Find all likely subtag entries whose region matches the default region.
+        default_replacements = {
+            (language, script)
+            for (language, script, region) in region_likely_subtags
+            if region == default
+        }
+
+        # And finally find those entries which don't use the default region.
+        # These are the entries we're actually interested in, because those need
+        # to be handled specially when selecting the correct preferred region.
+        non_default_replacements = [
+            (language, script, region)
+            for (language, script, region) in region_likely_subtags
+            if (language, script) not in default_replacements
+        ]
+
+        # If there are no non-default replacements, we can handle the region as
+        # part of the simple region mapping.
+        if non_default_replacements:
+            complex_region_mappings_final[deprecated_region] = (
+                default,
+                non_default_replacements,
+            )
+        else:
+            region_mappings[deprecated_region] = default
+
+    return {
+        "grandfatheredMappings": grandfathered_mappings,
+        "languageMappings": language_mappings,
+        "complexLanguageMappings": complex_language_mappings,
+        "regionMappings": region_mappings,
+        "complexRegionMappings": complex_region_mappings_final,
+        "variantMappings": variant_mappings,
+        "likelySubtags": likely_subtags,
+    }
+
+
+def readUnicodeExtensions(core_file):
+    import xml.etree.ElementTree as ET
+
+    # Match all xml-files in the BCP 47 directory.
+    bcpFileRE = re.compile(r"^common/bcp47/.+\.xml$")
+
+    # https://www.unicode.org/reports/tr35/#Unicode_locale_identifier
+    #
+    # type = alphanum{3,8} (sep alphanum{3,8})* ;
+    typeRE = re.compile(r"^[a-z0-9]{3,8}(-[a-z0-9]{3,8})*$")
+
+    # Mapping from Unicode extension types to dict of deprecated to
+    # preferred values.
+    mapping = {
+        # Unicode BCP 47 U Extension
+        "u": {},
+        # Unicode BCP 47 T Extension
+        "t": {},
+    }
+
+    def readBCP47File(file):
+        tree = ET.parse(file)
+        for keyword in tree.iterfind(".//keyword/key"):
+            extension = keyword.get("extension", "u")
+            assert (
+                extension == "u" or extension == "t"
+            ), "unknown extension type: {}".format(extension)
+
+            extension_name = keyword.get("name")
+
+            for type in keyword.iterfind("type"):
+                # <https://unicode.org/reports/tr35/#Unicode_Locale_Extension_Data_Files>:
+                #
+                # The key or type name used by Unicode locale extension with 'u' extension
+                # syntax or the 't' extensions syntax. When alias below is absent, this name
+                # can be also used with the old style "@key=type" syntax.
+                name = type.get("name")
+
+                # Ignore the special name:
+                # - <https://unicode.org/reports/tr35/#CODEPOINTS>
+                # - <https://unicode.org/reports/tr35/#REORDER_CODE>
+                # - <https://unicode.org/reports/tr35/#RG_KEY_VALUE>
+                # - <https://unicode.org/reports/tr35/#SUBDIVISION_CODE>
+                # - <https://unicode.org/reports/tr35/#PRIVATE_USE>
+                if name in (
+                    "CODEPOINTS",
+                    "REORDER_CODE",
+                    "RG_KEY_VALUE",
+                    "SUBDIVISION_CODE",
+                    "PRIVATE_USE",
+                ):
+                    continue
+
+                # All other names should match the 'type' production.
+                assert (
+                    typeRE.match(name) is not None
+                ), "{} matches the 'type' production".format(name)
+
+                # <https://unicode.org/reports/tr35/#Unicode_Locale_Extension_Data_Files>:
+                #
+                # The preferred value of the deprecated key, type or attribute element.
+                # When a key, type or attribute element is deprecated, this attribute is
+                # used for specifying a new canonical form if available.
+                preferred = type.get("preferred")
+
+                # <https://unicode.org/reports/tr35/#Unicode_Locale_Extension_Data_Files>:
+                #
+                # The BCP 47 form is the canonical form, and recommended. Other aliases are
+                # included only for backwards compatibility.
+                alias = type.get("alias")
+
+                # <https://unicode.org/reports/tr35/#Canonical_Unicode_Locale_Identifiers>
+                #
+                # Use the bcp47 data to replace keys, types, tfields, and tvalues by their
+                # canonical forms. See Section 3.6.4 U Extension Data Files) and Section
+                # 3.7.1 T Extension Data Files. The aliases are in the alias attribute
+                # value, while the canonical is in the name attribute value.
+
+                # 'preferred' contains the new preferred name, 'alias' the compatibility
+                # name, but then there's this entry where 'preferred' and 'alias' are the
+                # same. So which one to choose? Assume 'preferred' is the actual canonical
+                # name.
+                #
+                # <type name="islamicc"
+                #       description="Civil (algorithmic) Arabic calendar"
+                #       deprecated="true"
+                #       preferred="islamic-civil"
+                #       alias="islamic-civil"/>
+
+                if preferred is not None:
+                    assert typeRE.match(preferred), preferred
+                    mapping[extension].setdefault(extension_name, {})[name] = preferred
+
+                if alias is not None:
+                    for alias_name in alias.lower().split(" "):
+                        # Ignore alias entries which don't match the 'type' production.
+                        if typeRE.match(alias_name) is None:
+                            continue
+
+                        # See comment above when 'alias' and 'preferred' are both present.
+                        if (
+                            preferred is not None
+                            and name in mapping[extension][extension_name]
+                        ):
+                            continue
+
+                        # Skip over entries where 'name' and 'alias' are equal.
+                        #
+                        # <type name="pst8pdt"
+                        #       description="POSIX style time zone for US Pacific Time"
+                        #       alias="PST8PDT"
+                        #       since="1.8"/>
+                        if name == alias_name:
+                            continue
+
+                        mapping[extension].setdefault(extension_name, {})[
+                            alias_name
+                        ] = name
+
+    def readSupplementalMetadata(file):
+        # Find subdivision and region replacements.
+        #
+        # <https://www.unicode.org/reports/tr35/#Canonical_Unicode_Locale_Identifiers>
+        #
+        # Replace aliases in special key values:
+        #   - If there is an 'sd' or 'rg' key, replace any subdivision alias
+        #     in its value in the same way, using subdivisionAlias data.
+        tree = ET.parse(file)
+        for alias in tree.iterfind(".//subdivisionAlias"):
+            type = alias.get("type")
+            assert (
+                typeRE.match(type) is not None
+            ), "{} matches the 'type' production".format(type)
+
+            # Take the first replacement when multiple ones are present.
+            replacement = alias.get("replacement").split(" ")[0].lower()
+
+            # Skip over invalid replacements.
+            #
+            # <subdivisionAlias type="fi01" replacement="AX" reason="overlong"/>
+            #
+            # It's not entirely clear to me if CLDR actually wants to use
+            # "axzzzz" as the replacement for this case.
+            if typeRE.match(replacement) is None:
+                continue
+
+            # 'subdivisionAlias' applies to 'rg' and 'sd' keys.
+            mapping["u"].setdefault("rg", {})[type] = replacement
+            mapping["u"].setdefault("sd", {})[type] = replacement
+
+    for name in core_file.namelist():
+        if bcpFileRE.match(name):
+            readBCP47File(core_file.open(name))
+
+    readSupplementalMetadata(
+        core_file.open("common/supplemental/supplementalMetadata.xml")
+    )
+
+    return {
+        "unicodeMappings": mapping["u"],
+        "transformMappings": mapping["t"],
+    }
+
+
+def writeCLDRLanguageTagData(println, data, url):
+    """ Writes the language tag data to the Intl data file. """
+
+    println(generatedFileWarning)
+    println("// Version: CLDR-{}".format(data["version"]))
+    println("// URL: {}".format(url))
+
+    println(
+        """
+#include "mozilla/Assertions.h"
+#include "mozilla/Span.h"
+#include "mozilla/TextUtils.h"
+
+#include <algorithm>
+#include <cstdint>
+#include <cstring>
+#include <iterator>
+#include <string>
+#include <type_traits>
+
+#include "builtin/intl/LanguageTag.h"
+#include "util/Text.h"
+#include "vm/JSContext.h"
+
+using namespace js::intl::LanguageTagLimits;
+
+template <size_t Length, size_t TagLength, size_t SubtagLength>
+static inline bool HasReplacement(
+    const char (&subtags)[Length][TagLength],
+    const js::intl::LanguageTagSubtag<SubtagLength>& subtag) {
+  MOZ_ASSERT(subtag.length() == TagLength - 1,
+             "subtag must have the same length as the list of subtags");
+
+  const char* ptr = subtag.span().data();
+  return std::binary_search(std::begin(subtags), std::end(subtags), ptr,
+                            [](const char* a, const char* b) {
+    return memcmp(a, b, TagLength - 1) < 0;
+  });
+}
+
+template <size_t Length, size_t TagLength, size_t SubtagLength>
+static inline const char* SearchReplacement(
+    const char (&subtags)[Length][TagLength],
+    const char* (&aliases)[Length],
+    const js::intl::LanguageTagSubtag<SubtagLength>& subtag) {
+  MOZ_ASSERT(subtag.length() == TagLength - 1,
+             "subtag must have the same length as the list of subtags");
+
+  const char* ptr = subtag.span().data();
+  auto p = std::lower_bound(std::begin(subtags), std::end(subtags), ptr,
+                            [](const char* a, const char* b) {
+    return memcmp(a, b, TagLength - 1) < 0;
+  });
+  if (p != std::end(subtags) && memcmp(*p, ptr, TagLength - 1) == 0) {
+    return aliases[std::distance(std::begin(subtags), p)];
+  }
+  return nullptr;
+}
+
+#ifdef DEBUG
+static bool IsAsciiLowercaseAlphanumeric(char c) {
+  return mozilla::IsAsciiLowercaseAlpha(c) || mozilla::IsAsciiDigit(c);
+}
+
+static bool IsAsciiLowercaseAlphanumericOrDash(char c) {
+  return IsAsciiLowercaseAlphanumeric(c) || c == '-';
+}
+
+static bool IsCanonicallyCasedLanguageTag(mozilla::Span<const char> span) {
+  // Tell the analysis the |std::all_of| function can't GC.
+  JS::AutoSuppressGCAnalysis nogc;
+
+  return std::all_of(span.begin(), span.end(), mozilla::IsAsciiLowercaseAlpha<char>);
+}
+
+static bool IsCanonicallyCasedRegionTag(mozilla::Span<const char> span) {
+  // Tell the analysis the |std::all_of| function can't GC.
+  JS::AutoSuppressGCAnalysis nogc;
+
+  return std::all_of(span.begin(), span.end(), mozilla::IsAsciiUppercaseAlpha<char>) ||
+         std::all_of(span.begin(), span.end(), mozilla::IsAsciiDigit<char>);
+}
+
+static bool IsCanonicallyCasedVariantTag(mozilla::Span<const char> span) {
+  // Tell the analysis the |std::all_of| function can't GC.
+  JS::AutoSuppressGCAnalysis nogc;
+
+  return std::all_of(span.begin(), span.end(), IsAsciiLowercaseAlphanumeric);
+}
+
+static bool IsCanonicallyCasedUnicodeKey(mozilla::Span<const char> key) {
+  return std::all_of(key.begin(), key.end(), IsAsciiLowercaseAlphanumeric);
+}
+
+static bool IsCanonicallyCasedUnicodeType(mozilla::Span<const char> type) {
+  return std::all_of(type.begin(), type.end(), IsAsciiLowercaseAlphanumericOrDash);
+}
+
+static bool IsCanonicallyCasedTransformKey(mozilla::Span<const char> key) {
+  return std::all_of(key.begin(), key.end(), IsAsciiLowercaseAlphanumeric);
+}
+
+static bool IsCanonicallyCasedTransformType(mozilla::Span<const char> type) {
+  return std::all_of(type.begin(), type.end(), IsAsciiLowercaseAlphanumericOrDash);
+}
+#endif
+""".rstrip()
+    )
+
+    source = "CLDR Supplemental Data, version {}".format(data["version"])
+    grandfathered_mappings = data["grandfatheredMappings"]
+    language_mappings = data["languageMappings"]
+    complex_language_mappings = data["complexLanguageMappings"]
+    region_mappings = data["regionMappings"]
+    complex_region_mappings = data["complexRegionMappings"]
+    variant_mappings = data["variantMappings"]
+    unicode_mappings = data["unicodeMappings"]
+    transform_mappings = data["transformMappings"]
+
+    # unicode_language_subtag = alpha{2,3} | alpha{5,8} ;
+    language_maxlength = 8
+
+    # unicode_region_subtag = (alpha{2} | digit{3}) ;
+    region_maxlength = 3
+
+    writeMappingsBinarySearch(
+        println,
+        "languageMapping",
+        "LanguageSubtag&",
+        "language",
+        "IsStructurallyValidLanguageTag",
+        "IsCanonicallyCasedLanguageTag",
+        language_mappings,
+        language_maxlength,
+        "Mappings from language subtags to preferred values.",
+        source,
+        url,
+    )
+    writeMappingsBinarySearch(
+        println,
+        "complexLanguageMapping",
+        "const LanguageSubtag&",
+        "language",
+        "IsStructurallyValidLanguageTag",
+        "IsCanonicallyCasedLanguageTag",
+        complex_language_mappings.keys(),
+        language_maxlength,
+        "Language subtags with complex mappings.",
+        source,
+        url,
+    )
+    writeMappingsBinarySearch(
+        println,
+        "regionMapping",
+        "RegionSubtag&",
+        "region",
+        "IsStructurallyValidRegionTag",
+        "IsCanonicallyCasedRegionTag",
+        region_mappings,
+        region_maxlength,
+        "Mappings from region subtags to preferred values.",
+        source,
+        url,
+    )
+    writeMappingsBinarySearch(
+        println,
+        "complexRegionMapping",
+        "const RegionSubtag&",
+        "region",
+        "IsStructurallyValidRegionTag",
+        "IsCanonicallyCasedRegionTag",
+        complex_region_mappings.keys(),
+        region_maxlength,
+        "Region subtags with complex mappings.",
+        source,
+        url,
+    )
+
+    writeComplexLanguageTagMappings(
+        println,
+        complex_language_mappings,
+        "Language subtags with complex mappings.",
+        source,
+        url,
+    )
+    writeComplexRegionTagMappings(
+        println,
+        complex_region_mappings,
+        "Region subtags with complex mappings.",
+        source,
+        url,
+    )
+
+    writeVariantTagMappings(
+        println,
+        variant_mappings,
+        "Mappings from variant subtags to preferred values.",
+        source,
+        url,
+    )
+
+    writeGrandfatheredMappingsFunction(
+        println,
+        grandfathered_mappings,
+        "Canonicalize grandfathered locale identifiers.",
+        source,
+        url,
+    )
+
+    writeUnicodeExtensionsMappings(println, unicode_mappings, "Unicode")
+    writeUnicodeExtensionsMappings(println, transform_mappings, "Transform")
+
+
+def writeCLDRLanguageTagLikelySubtagsTest(println, data, url):
+    """ Writes the likely-subtags test file. """
+
+    println(generatedFileWarning)
+
+    source = "CLDR Supplemental Data, version {}".format(data["version"])
+    language_mappings = data["languageMappings"]
+    complex_language_mappings = data["complexLanguageMappings"]
+    region_mappings = data["regionMappings"]
+    complex_region_mappings = data["complexRegionMappings"]
+    likely_subtags = data["likelySubtags"]
+
+    def bcp47(tag):
+        (language, script, region) = tag
+        return "{}{}{}".format(
+            language, "-" + script if script else "", "-" + region if region else ""
+        )
+
+    def canonical(tag):
+        (language, script, region) = tag
+
+        # Map deprecated language subtags.
+        if language in language_mappings:
+            language = language_mappings[language]
+        elif language in complex_language_mappings:
+            (language2, script2, region2) = complex_language_mappings[language]
+            (language, script, region) = (
+                language2,
+                script if script else script2,
+                region if region else region2,
+            )
+
+        # Map deprecated region subtags.
+        if region in region_mappings:
+            region = region_mappings[region]
+        else:
+            # Assume no complex region mappings are needed for now.
+            assert (
+                region not in complex_region_mappings
+            ), "unexpected region with complex mappings: {}".format(region)
+
+        return (language, script, region)
+
+    # https://unicode.org/reports/tr35/#Likely_Subtags
+
+    def addLikelySubtags(tag):
+        # Step 1: Canonicalize.
+        (language, script, region) = canonical(tag)
+        if script == "Zzzz":
+            script = None
+        if region == "ZZ":
+            region = None
+
+        # Step 2: Lookup.
+        searches = (
+            (language, script, region),
+            (language, None, region),
+            (language, script, None),
+            (language, None, None),
+            ("und", script, None),
+        )
+        search = next(search for search in searches if search in likely_subtags)
+
+        (language_s, script_s, region_s) = search
+        (language_m, script_m, region_m) = likely_subtags[search]
+
+        # Step 3: Return.
+        return (
+            language if language != language_s else language_m,
+            script if script != script_s else script_m,
+            region if region != region_s else region_m,
+        )
+
+    # https://unicode.org/reports/tr35/#Likely_Subtags
+    def removeLikelySubtags(tag):
+        # Step 1: Add likely subtags.
+        max = addLikelySubtags(tag)
+
+        # Step 2: Remove variants (doesn't apply here).
+
+        # Step 3: Find a match.
+        (language, script, region) = max
+        for trial in (
+            (language, None, None),
+            (language, None, region),
+            (language, script, None),
+        ):
+            if addLikelySubtags(trial) == max:
+                return trial
+
+        # Step 4: Return maximized if no match found.
+        return max
+
+    def likely_canonical(from_tag, to_tag):
+        # Canonicalize the input tag.
+        from_tag = canonical(from_tag)
+
+        # Update the expected result if necessary.
+        if from_tag in likely_subtags:
+            to_tag = likely_subtags[from_tag]
+
+        # Canonicalize the expected output.
+        to_canonical = canonical(to_tag)
+
+        # Sanity check: This should match the result of |addLikelySubtags|.
+        assert to_canonical == addLikelySubtags(from_tag)
+
+        return to_canonical
+
+    # |likely_subtags| contains non-canonicalized tags, so canonicalize it first.
+    likely_subtags_canonical = {
+        k: likely_canonical(k, v) for (k, v) in likely_subtags.items()
+    }
+
+    # Add test data for |Intl.Locale.prototype.maximize()|.
+    writeMappingsVar(
+        println,
+        {bcp47(k): bcp47(v) for (k, v) in likely_subtags_canonical.items()},
+        "maxLikelySubtags",
+        "Extracted from likelySubtags.xml.",
+        source,
+        url,
+    )
+
+    # Use the maximalized tags as the input for the remove likely-subtags test.
+    minimized = {
+        tag: removeLikelySubtags(tag) for tag in likely_subtags_canonical.values()
+    }
+
+    # Add test data for |Intl.Locale.prototype.minimize()|.
+    writeMappingsVar(
+        println,
+        {bcp47(k): bcp47(v) for (k, v) in minimized.items()},
+        "minLikelySubtags",
+        "Extracted from likelySubtags.xml.",
+        source,
+        url,
+    )
+
+    println(
+        """
+for (let [tag, maximal] of Object.entries(maxLikelySubtags)) {
+    assertEq(new Intl.Locale(tag).maximize().toString(), maximal);
+}"""
+    )
+
+    println(
+        """
+for (let [tag, minimal] of Object.entries(minLikelySubtags)) {
+    assertEq(new Intl.Locale(tag).minimize().toString(), minimal);
+}"""
+    )
+
+    println(
+        """
+if (typeof reportCompare === "function")
+    reportCompare(0, 0);"""
+    )
+
+
+def readCLDRVersionFromICU():
+    icuDir = os.path.join(topsrcdir, "intl/icu/source")
+    if not os.path.isdir(icuDir):
+        raise RuntimeError("not a directory: {}".format(icuDir))
+
+    reVersion = re.compile(r'\s*cldrVersion\{"(\d+(?:\.\d+)?)"\}')
+
+    for line in flines(os.path.join(icuDir, "data/misc/supplementalData.txt")):
+        m = reVersion.match(line)
+        if m:
+            version = m.group(1)
+            break
+
+    if version is None:
+        raise RuntimeError("can't resolve CLDR version")
+
+    return version
+
+
+def updateCLDRLangTags(args):
+    """ Update the LanguageTagGenerated.cpp file. """
+    version = args.version
+    url = args.url
+    out = args.out
+    filename = args.file
+
+    # Determine current CLDR version from ICU.
+    if version is None:
+        version = readCLDRVersionFromICU()
+
+    url = url.replace("<VERSION>", version)
+
+    print("Arguments:")
+    print("\tCLDR version: %s" % version)
+    print("\tDownload url: %s" % url)
+    if filename is not None:
+        print("\tLocal CLDR core.zip file: %s" % filename)
+    print("\tOutput file: %s" % out)
+    print("")
+
+    data = {
+        "version": version,
+    }
+
+    def readFiles(cldr_file):
+        with ZipFile(cldr_file) as zip_file:
+            data.update(readSupplementalData(zip_file))
+            data.update(readUnicodeExtensions(zip_file))
+
+    print("Processing CLDR data...")
+    if filename is not None:
+        print("Always make sure you have the newest CLDR core.zip!")
+        with open(filename, "rb") as cldr_file:
+            readFiles(cldr_file)
+    else:
+        print("Downloading CLDR core.zip...")
+        with closing(urlopen(url)) as cldr_file:
+            cldr_data = io.BytesIO(cldr_file.read())
+            readFiles(cldr_data)
+
+    print("Writing Intl data...")
+    with io.open(out, mode="w", encoding="utf-8", newline="") as f:
+        println = partial(print, file=f)
+
+        writeCLDRLanguageTagData(println, data, url)
+
+    print("Writing Intl test data...")
+    js_src_builtin_intl_dir = os.path.dirname(os.path.abspath(__file__))
+    test_file = os.path.join(
+        js_src_builtin_intl_dir,
+        "../../tests/non262/Intl/Locale/likely-subtags-generated.js",
+    )
+    with io.open(test_file, mode="w", encoding="utf-8", newline="") as f:
+        println = partial(print, file=f)
+
+        println("// |reftest| skip-if(!this.hasOwnProperty('Intl'))")
+        writeCLDRLanguageTagLikelySubtagsTest(println, data, url)
+
+
+def flines(filepath, encoding="utf-8"):
+    """ Open filepath and iterate over its content. """
+    with io.open(filepath, mode="r", encoding=encoding) as f:
+        for line in f:
+            yield line
+
+
+@total_ordering
+class Zone(object):
+    """ Time zone with optional file name. """
+
+    def __init__(self, name, filename=""):
+        self.name = name
+        self.filename = filename
+
+    def __eq__(self, other):
+        return hasattr(other, "name") and self.name == other.name
+
+    def __lt__(self, other):
+        return self.name < other.name
+
+    def __hash__(self):
+        return hash(self.name)
+
+    def __str__(self):
+        return self.name
+
+    def __repr__(self):
+        return self.name
+
+
+class TzDataDir(object):
+    """ tzdata source from a directory. """
+
+    def __init__(self, obj):
+        self.name = partial(os.path.basename, obj)
+        self.resolve = partial(os.path.join, obj)
+        self.basename = os.path.basename
+        self.isfile = os.path.isfile
+        self.listdir = partial(os.listdir, obj)
+        self.readlines = flines
+
+
+class TzDataFile(object):
+    """ tzdata source from a file (tar or gzipped). """
+
+    def __init__(self, obj):
+        self.name = lambda: os.path.splitext(
+            os.path.splitext(os.path.basename(obj))[0]
+        )[0]
+        self.resolve = obj.getmember
+        self.basename = attrgetter("name")
+        self.isfile = tarfile.TarInfo.isfile
+        self.listdir = obj.getnames
+        self.readlines = partial(self._tarlines, obj)
+
+    def _tarlines(self, tar, m):
+        with closing(tar.extractfile(m)) as f:
+            for line in f:
+                yield line.decode("utf-8")
+
+
+def validateTimeZones(zones, links):
+    """ Validate the zone and link entries. """
+    linkZones = set(links.keys())
+    intersect = linkZones.intersection(zones)
+    if intersect:
+        raise RuntimeError("Links also present in zones: %s" % intersect)
+
+    zoneNames = {z.name for z in zones}
+    linkTargets = set(links.values())
+    if not linkTargets.issubset(zoneNames):
+        raise RuntimeError(
+            "Link targets not found: %s" % linkTargets.difference(zoneNames)
+        )
+
+
+def partition(iterable, *predicates):
+    def innerPartition(pred, it):
+        it1, it2 = tee(it)
+        return (filter(pred, it1), filterfalse(pred, it2))
+
+    if len(predicates) == 0:
+        return iterable
+    (left, right) = innerPartition(predicates[0], iterable)
+    if len(predicates) == 1:
+        return (left, right)
+    return tuple([left] + list(partition(right, *predicates[1:])))
+
+
+def listIANAFiles(tzdataDir):
+    def isTzFile(d, m, f):
+        return m(f) and d.isfile(d.resolve(f))
+
+    return filter(
+        partial(isTzFile, tzdataDir, re.compile("^[a-z0-9]+$").match),
+        tzdataDir.listdir(),
+    )
+
+
+def readIANAFiles(tzdataDir, files):
+    """ Read all IANA time zone files from the given iterable. """
+    nameSyntax = "[\w/+\-]+"
+    pZone = re.compile(r"Zone\s+(?P<name>%s)\s+.*" % nameSyntax)
+    pLink = re.compile(
+        r"Link\s+(?P<target>%s)\s+(?P<name>%s)(?:\s+#.*)?" % (nameSyntax, nameSyntax)
+    )
+
+    def createZone(line, fname):
+        match = pZone.match(line)
+        name = match.group("name")
+        return Zone(name, fname)
+
+    def createLink(line, fname):
+        match = pLink.match(line)
+        (name, target) = match.group("name", "target")
+        return (Zone(name, fname), target)
+
+    zones = set()
+    links = dict()
+    for filename in files:
+        filepath = tzdataDir.resolve(filename)
+        for line in tzdataDir.readlines(filepath):
+            if line.startswith("Zone"):
+                zones.add(createZone(line, filename))
+            if line.startswith("Link"):
+                (link, target) = createLink(line, filename)
+                links[link] = target
+
+    return (zones, links)
+
+
+def readIANATimeZones(tzdataDir, ignoreBackzone, ignoreFactory):
+    """ Read the IANA time zone information from `tzdataDir`. """
+
+    backzoneFiles = {"backzone"}
+    (bkfiles, tzfiles) = partition(listIANAFiles(tzdataDir), backzoneFiles.__contains__)
+
+    # Read zone and link infos.
+    (zones, links) = readIANAFiles(tzdataDir, tzfiles)
+    (backzones, backlinks) = readIANAFiles(tzdataDir, bkfiles)
+
+    # Remove the placeholder time zone "Factory".
+    if ignoreFactory:
+        zones.remove(Zone("Factory"))
+
+    # Merge with backzone data.
+    if not ignoreBackzone:
+        zones |= backzones
+        links = {
+            name: target for name, target in links.items() if name not in backzones
+        }
+        links.update(backlinks)
+
+    validateTimeZones(zones, links)
+
+    return (zones, links)
+
+
+def readICUResourceFile(filename):
+    """Read an ICU resource file.
+
+    Yields (<table-name>, <startOrEnd>, <value>) for each table.
+    """
+
+    numberValue = r"-?\d+"
+    stringValue = r'".+?"'
+
+    def asVector(val):
+        return r"%s(?:\s*,\s*%s)*" % (val, val)
+
+    numberVector = asVector(numberValue)
+    stringVector = asVector(stringValue)
+
+    reNumberVector = re.compile(numberVector)
+    reStringVector = re.compile(stringVector)
+    reNumberValue = re.compile(numberValue)
+    reStringValue = re.compile(stringValue)
+
+    def parseValue(value):
+        m = reNumberVector.match(value)
+        if m:
+            return [int(v) for v in reNumberValue.findall(value)]
+        m = reStringVector.match(value)
+        if m:
+            return [v[1:-1] for v in reStringValue.findall(value)]
+        raise RuntimeError("unknown value type: %s" % value)
+
+    def extractValue(values):
+        if len(values) == 0:
+            return None
+        if len(values) == 1:
+            return values[0]
+        return values
+
+    def line(*args):
+        maybeMultiComments = r"(?:/\*[^*]*\*/)*"
+        maybeSingleComment = r"(?://.*)?"
+        lineStart = "^%s" % maybeMultiComments
+        lineEnd = "%s\s*%s$" % (maybeMultiComments, maybeSingleComment)
+        return re.compile(r"\s*".join(chain([lineStart], args, [lineEnd])))
+
+    tableName = r'(?P<quote>"?)(?P<name>.+?)(?P=quote)'
+    tableValue = r"(?P<value>%s|%s)" % (numberVector, stringVector)
+
+    reStartTable = line(tableName, r"\{")
+    reEndTable = line(r"\}")
+    reSingleValue = line(r",?", tableValue, r",?")
+    reCompactTable = line(tableName, r"\{", tableValue, r"\}")
+    reEmptyLine = line()
+
+    tables = []
+
+    def currentTable():
+        return "|".join(tables)
+
+    values = []
+    for line in flines(filename, "utf-8-sig"):
+        line = line.strip()
+        if line == "":
+            continue
+
+        m = reEmptyLine.match(line)
+        if m:
+            continue
+
+        m = reStartTable.match(line)
+        if m:
+            assert len(values) == 0
+            tables.append(m.group("name"))
+            continue
+
+        m = reEndTable.match(line)
+        if m:
+            yield (currentTable(), extractValue(values))
+            tables.pop()
+            values = []
+            continue
+
+        m = reCompactTable.match(line)
+        if m:
+            assert len(values) == 0
+            tables.append(m.group("name"))
+            yield (currentTable(), extractValue(parseValue(m.group("value"))))
+            tables.pop()
+            continue
+
+        m = reSingleValue.match(line)
+        if m and tables:
+            values.extend(parseValue(m.group("value")))
+            continue
+
+        raise RuntimeError("unknown entry: %s" % line)
+
+
+def readICUTimeZonesFromTimezoneTypes(icuTzDir):
+    """Read the ICU time zone information from `icuTzDir`/timezoneTypes.txt
+    and returns the tuple (zones, links).
+    """
+    typeMapTimeZoneKey = "timezoneTypes:table(nofallback)|typeMap|timezone|"
+    typeAliasTimeZoneKey = "timezoneTypes:table(nofallback)|typeAlias|timezone|"
+
+    def toTimeZone(name):
+        return Zone(name.replace(":", "/"))
+
+    zones = set()
+    links = dict()
+
+    for name, value in readICUResourceFile(os.path.join(icuTzDir, "timezoneTypes.txt")):
+        if name.startswith(typeMapTimeZoneKey):
+            zones.add(toTimeZone(name[len(typeMapTimeZoneKey) :]))
+        if name.startswith(typeAliasTimeZoneKey):
+            links[toTimeZone(name[len(typeAliasTimeZoneKey) :])] = value
+
+    validateTimeZones(zones, links)
+
+    return (zones, links)
+
+
+def readICUTimeZonesFromZoneInfo(icuTzDir):
+    """Read the ICU time zone information from `icuTzDir`/zoneinfo64.txt
+    and returns the tuple (zones, links).
+    """
+    zoneKey = "zoneinfo64:table(nofallback)|Zones:array|:table"
+    linkKey = "zoneinfo64:table(nofallback)|Zones:array|:int"
+    namesKey = "zoneinfo64:table(nofallback)|Names"
+
+    tzId = 0
+    tzLinks = dict()
+    tzNames = []
+
+    for name, value in readICUResourceFile(os.path.join(icuTzDir, "zoneinfo64.txt")):
+        if name == zoneKey:
+            tzId += 1
+        elif name == linkKey:
+            tzLinks[tzId] = int(value)
+            tzId += 1
+        elif name == namesKey:
+            tzNames.extend(value)
+
+    links = {Zone(tzNames[zone]): tzNames[target] for (zone, target) in tzLinks.items()}
+    zones = {Zone(v) for v in tzNames if Zone(v) not in links}
+
+    validateTimeZones(zones, links)
+
+    return (zones, links)
+
+
+def readICUTimeZones(icuDir, icuTzDir, ignoreFactory):
+    # zoneinfo64.txt contains the supported time zones by ICU. This data is
+    # generated from tzdata files, it doesn't include "backzone" in stock ICU.
+    (zoneinfoZones, zoneinfoLinks) = readICUTimeZonesFromZoneInfo(icuTzDir)
+
+    # timezoneTypes.txt contains the canonicalization information for ICU. This
+    # data is generated from CLDR files. It includes data about time zones from
+    # tzdata's "backzone" file.
+    (typesZones, typesLinks) = readICUTimeZonesFromTimezoneTypes(icuTzDir)
+
+    # Remove the placeholder time zone "Factory".
+    # See also <https://github.com/eggert/tz/blob/master/factory>.
+    if ignoreFactory:
+        zoneinfoZones.remove(Zone("Factory"))
+
+    # Remove the ICU placeholder time zone "Etc/Unknown".
+    # See also <https://unicode.org/reports/tr35/#Time_Zone_Identifiers>.
+    for zones in (zoneinfoZones, typesZones):
+        zones.remove(Zone("Etc/Unknown"))
+
+    # Remove any outdated ICU links.
+    for links in (zoneinfoLinks, typesLinks):
+        for zone in otherICULegacyLinks().keys():
+            if zone not in links:
+                raise KeyError(f"Can't remove non-existent link from '{zone}'")
+            del links[zone]
+
+    # Information in zoneinfo64 should be a superset of timezoneTypes.
+    def inZoneInfo64(zone):
+        return zone in zoneinfoZones or zone in zoneinfoLinks
+
+    notFoundInZoneInfo64 = [zone for zone in typesZones if not inZoneInfo64(zone)]
+    if notFoundInZoneInfo64:
+        raise RuntimeError(
+            "Missing time zones in zoneinfo64.txt: %s" % notFoundInZoneInfo64
+        )
+
+    notFoundInZoneInfo64 = [
+        zone for zone in typesLinks.keys() if not inZoneInfo64(zone)
+    ]
+    if notFoundInZoneInfo64:
+        raise RuntimeError(
+            "Missing time zones in zoneinfo64.txt: %s" % notFoundInZoneInfo64
+        )
+
+    # zoneinfo64.txt only defines the supported time zones by ICU, the canonicalization
+    # rules are defined through timezoneTypes.txt. Merge both to get the actual zones
+    # and links used by ICU.
+    icuZones = set(
+        chain(
+            (zone for zone in zoneinfoZones if zone not in typesLinks),
+            (zone for zone in typesZones),
+        )
+    )
+    icuLinks = dict(
+        chain(
+            (
+                (zone, target)
+                for (zone, target) in zoneinfoLinks.items()
+                if zone not in typesZones
+            ),
+            ((zone, target) for (zone, target) in typesLinks.items()),
+        )
+    )
+
+    return (icuZones, icuLinks)
+
+
+def readICULegacyZones(icuDir):
+    """Read the ICU legacy time zones from `icuTzDir`/tools/tzcode/icuzones
+    and returns the tuple (zones, links).
+    """
+    tzdir = TzDataDir(os.path.join(icuDir, "tools/tzcode"))
+
+    # Per spec we must recognize only IANA time zones and links, but ICU
+    # recognizes various legacy, non-IANA time zones and links. Compute these
+    # non-IANA time zones and links.
+
+    # Most legacy, non-IANA time zones and links are in the icuzones file.
+    (zones, links) = readIANAFiles(tzdir, ["icuzones"])
+
+    # Remove the ICU placeholder time zone "Etc/Unknown".
+    # See also <https://unicode.org/reports/tr35/#Time_Zone_Identifiers>.
+    zones.remove(Zone("Etc/Unknown"))
+
+    # A handful of non-IANA zones/links are not in icuzones and must be added
+    # manually so that we won't invoke ICU with them.
+    for (zone, target) in otherICULegacyLinks().items():
+        if zone in links:
+            if links[zone] != target:
+                raise KeyError(
+                    f"Can't overwrite link '{zone} -> {links[zone]}' with '{target}'"
+                )
+            else:
+                print(
+                    f"Info: Link '{zone} -> {target}' can be removed from otherICULegacyLinks()"
+                )
+        links[zone] = target
+
+    return (zones, links)
+
+
+def otherICULegacyLinks():
+    """The file `icuTzDir`/tools/tzcode/icuzones contains all ICU legacy time
+    zones with the exception of time zones which are removed by IANA after an
+    ICU release.
+
+    For example ICU 67 uses tzdata2018i, but tzdata2020b removed the link from
+    "US/Pacific-New" to "America/Los_Angeles". ICU standalone tzdata updates
+    don't include modified icuzones files, so we must manually record any IANA
+    modifications here.
+
+    After an ICU update, we can remove any no longer needed entries from this
+    function by checking if the relevant entries are now included in icuzones.
+    """
+
+    return {
+        # tzdata2020b removed the link US/Pacific-New -> America/Los_Angeles.
+        Zone("US/Pacific-New"): "America/Los_Angeles",
+    }
+
+
+def icuTzDataVersion(icuTzDir):
+    """ Read the ICU time zone version from `icuTzDir`/zoneinfo64.txt. """
+
+    def searchInFile(pattern, f):
+        p = re.compile(pattern)
+        for line in flines(f, "utf-8-sig"):
+            m = p.search(line)
+            if m:
+                return m.group(1)
+        return None
+
+    zoneinfo = os.path.join(icuTzDir, "zoneinfo64.txt")
+    if not os.path.isfile(zoneinfo):
+        raise RuntimeError("file not found: %s" % zoneinfo)
+    version = searchInFile("^//\s+tz version:\s+([0-9]{4}[a-z])$", zoneinfo)
+    if version is None:
+        raise RuntimeError(
+            "%s does not contain a valid tzdata version string" % zoneinfo
+        )
+    return version
+
+
+def findIncorrectICUZones(ianaZones, ianaLinks, icuZones, icuLinks, ignoreBackzone):
+    """ Find incorrect ICU zone entries. """
+
+    def isIANATimeZone(zone):
+        return zone in ianaZones or zone in ianaLinks
+
+    def isICUTimeZone(zone):
+        return zone in icuZones or zone in icuLinks
+
+    def isICULink(zone):
+        return zone in icuLinks
+
+    # All IANA zones should be present in ICU.
+    missingTimeZones = [zone for zone in ianaZones if not isICUTimeZone(zone)]
+    # Normally zones in backzone are also present as links in one of the other
+    # time zone files. The only exception to this rule is the Asia/Hanoi time
+    # zone, this zone is only present in the backzone file.
+    expectedMissing = [] if ignoreBackzone else [Zone("Asia/Hanoi")]
+    if missingTimeZones != expectedMissing:
+        raise RuntimeError(
+            "Not all zones are present in ICU, did you forget "
+            "to run intl/update-tzdata.sh? %s" % missingTimeZones
+        )
+
+    # Zones which are only present in ICU?
+    additionalTimeZones = [zone for zone in icuZones if not isIANATimeZone(zone)]
+    if additionalTimeZones:
+        raise RuntimeError(
+            "Additional zones present in ICU, did you forget "
+            "to run intl/update-tzdata.sh? %s" % additionalTimeZones
+        )
+
+    # Zones which are marked as links in ICU.
+    result = ((zone, icuLinks[zone]) for zone in ianaZones if isICULink(zone))
+
+    # Remove unnecessary UTC mappings.
+    utcnames = ["Etc/UTC", "Etc/UCT", "Etc/GMT"]
+    result = ((zone, target) for (zone, target) in result if zone.name not in utcnames)
+
+    return sorted(result, key=itemgetter(0))
+
+
+def findIncorrectICULinks(ianaZones, ianaLinks, icuZones, icuLinks):
+    """ Find incorrect ICU link entries. """
+
+    def isIANATimeZone(zone):
+        return zone in ianaZones or zone in ianaLinks
+
+    def isICUTimeZone(zone):
+        return zone in icuZones or zone in icuLinks
+
+    def isICULink(zone):
+        return zone in icuLinks
+
+    def isICUZone(zone):
+        return zone in icuZones
+
+    # All links should be present in ICU.
+    missingTimeZones = [zone for zone in ianaLinks.keys() if not isICUTimeZone(zone)]
+    if missingTimeZones:
+        raise RuntimeError(
+            "Not all zones are present in ICU, did you forget "
+            "to run intl/update-tzdata.sh? %s" % missingTimeZones
+        )
+
+    # Links which are only present in ICU?
+    additionalTimeZones = [zone for zone in icuLinks.keys() if not isIANATimeZone(zone)]
+    if additionalTimeZones:
+        raise RuntimeError(
+            "Additional links present in ICU, did you forget "
+            "to run intl/update-tzdata.sh? %s" % additionalTimeZones
+        )
+
+    result = chain(
+        # IANA links which have a different target in ICU.
+        (
+            (zone, target, icuLinks[zone])
+            for (zone, target) in ianaLinks.items()
+            if isICULink(zone) and target != icuLinks[zone]
+        ),
+        # IANA links which are zones in ICU.
+        (
+            (zone, target, zone.name)
+            for (zone, target) in ianaLinks.items()
+            if isICUZone(zone)
+        ),
+    )
+
+    # Remove unnecessary UTC mappings.
+    utcnames = ["Etc/UTC", "Etc/UCT", "Etc/GMT"]
+    result = (
+        (zone, target, icuTarget)
+        for (zone, target, icuTarget) in result
+        if target not in utcnames or icuTarget not in utcnames
+    )
+
+    return sorted(result, key=itemgetter(0))
+
+
+generatedFileWarning = "// Generated by make_intl_data.py. DO NOT EDIT."
+tzdataVersionComment = "// tzdata version = {0}"
+
+
+def processTimeZones(
+    tzdataDir, icuDir, icuTzDir, version, ignoreBackzone, ignoreFactory, out
+):
+    """ Read the time zone info and create a new time zone cpp file. """
+    print("Processing tzdata mapping...")
+    (ianaZones, ianaLinks) = readIANATimeZones(tzdataDir, ignoreBackzone, ignoreFactory)
+    (icuZones, icuLinks) = readICUTimeZones(icuDir, icuTzDir, ignoreFactory)
+    (legacyZones, legacyLinks) = readICULegacyZones(icuDir)
+
+    # Remove all legacy ICU time zones.
+    icuZones = {zone for zone in icuZones if zone not in legacyZones}
+    icuLinks = {
+        zone: target for (zone, target) in icuLinks.items() if zone not in legacyLinks
+    }
+
+    incorrectZones = findIncorrectICUZones(
+        ianaZones, ianaLinks, icuZones, icuLinks, ignoreBackzone
+    )
+    if not incorrectZones:
+        print("<<< No incorrect ICU time zones found, please update Intl.js! >>>")
+        print("<<< Maybe https://ssl.icu-project.org/trac/ticket/12044 was fixed? >>>")
+
+    incorrectLinks = findIncorrectICULinks(ianaZones, ianaLinks, icuZones, icuLinks)
+    if not incorrectLinks:
+        print("<<< No incorrect ICU time zone links found, please update Intl.js! >>>")
+        print("<<< Maybe https://ssl.icu-project.org/trac/ticket/12044 was fixed? >>>")
+
+    print("Writing Intl tzdata file...")
+    with io.open(out, mode="w", encoding="utf-8", newline="") as f:
+        println = partial(print, file=f)
+
+        println(generatedFileWarning)
+        println(tzdataVersionComment.format(version))
+        println("")
+
+        println("#ifndef builtin_intl_TimeZoneDataGenerated_h")
+        println("#define builtin_intl_TimeZoneDataGenerated_h")
+        println("")
+
+        println("namespace js {")
+        println("namespace timezone {")
+        println("")
+
+        println("// Format:")
+        println('// "ZoneName" // ICU-Name [time zone file]')
+        println("const char* const ianaZonesTreatedAsLinksByICU[] = {")
+        for (zone, icuZone) in incorrectZones:
+            println('    "%s", // %s [%s]' % (zone, icuZone, zone.filename))
+        println("};")
+        println("")
+
+        println("// Format:")
+        println('// "LinkName", "Target" // ICU-Target [time zone file]')
+        println("struct LinkAndTarget")
+        println("{")
+        println("    const char* const link;")
+        println("    const char* const target;")
+        println("};")
+        println("")
+        println("const LinkAndTarget ianaLinksCanonicalizedDifferentlyByICU[] = {")
+        for (zone, target, icuTarget) in incorrectLinks:
+            println(
+                '    { "%s", "%s" }, // %s [%s]'
+                % (zone, target, icuTarget, zone.filename)
+            )
+        println("};")
+        println("")
+
+        println(
+            "// Legacy ICU time zones, these are not valid IANA time zone names. We also"
+        )
+        println("// disallow the old and deprecated System V time zones.")
+        println(
+            "// https://ssl.icu-project.org/repos/icu/trunk/icu4c/source/tools/tzcode/icuzones"
+        )  # NOQA: E501
+        println("const char* const legacyICUTimeZones[] = {")
+        for zone in chain(sorted(legacyLinks.keys()), sorted(legacyZones)):
+            println('    "%s",' % zone)
+        println("};")
+        println("")
+
+        println("} // namespace timezone")
+        println("} // namespace js")
+        println("")
+        println("#endif /* builtin_intl_TimeZoneDataGenerated_h */")
+
+
+def updateBackzoneLinks(tzdataDir, links):
+    def withZone(fn):
+        return lambda zone_target: fn(zone_target[0])
+
+    (backzoneZones, backzoneLinks) = readIANAFiles(tzdataDir, ["backzone"])
+    (stableZones, updatedLinks, updatedZones) = partition(
+        links.items(),
+        # Link not changed in backzone.
+        withZone(lambda zone: zone not in backzoneLinks and zone not in backzoneZones),
+        # Link has a new target.
+        withZone(lambda zone: zone in backzoneLinks),
+    )
+    # Keep stable zones and links with updated target.
+    return dict(
+        chain(
+            stableZones,
+            map(withZone(lambda zone: (zone, backzoneLinks[zone])), updatedLinks),
+        )
+    )
+
+
+def generateTzDataLinkTestContent(testDir, version, fileName, description, links):
+    with io.open(
+        os.path.join(testDir, fileName), mode="w", encoding="utf-8", newline=""
+    ) as f:
+        println = partial(print, file=f)
+
+        println('// |reftest| skip-if(!this.hasOwnProperty("Intl"))')
+        println("")
+        println(generatedFileWarning)
+        println(tzdataVersionComment.format(version))
+        println(
+            """
+const tzMapper = [
+    x => x,
+    x => x.toUpperCase(),
+    x => x.toLowerCase(),
+];
+"""
+        )
+
+        println(description)
+        println("const links = {")
+        for (zone, target) in sorted(links, key=itemgetter(0)):
+            println('    "%s": "%s",' % (zone, target))
+        println("};")
+
+        println(
+            """
+for (let [linkName, target] of Object.entries(links)) {
+    if (target === "Etc/UTC" || target === "Etc/GMT")
+        target = "UTC";
+
+    for (let map of tzMapper) {
+        let dtf = new Intl.DateTimeFormat(undefined, {timeZone: map(linkName)});
+        let resolvedTimeZone = dtf.resolvedOptions().timeZone;
+        assertEq(resolvedTimeZone, target, `${linkName} -> ${target}`);
+    }
+}
+"""
+        )
+        println(
+            """
+if (typeof reportCompare === "function")
+    reportCompare(0, 0, "ok");
+"""
+        )
+
+
+def generateTzDataTestBackwardLinks(tzdataDir, version, ignoreBackzone, testDir):
+    (zones, links) = readIANAFiles(tzdataDir, ["backward"])
+    assert len(zones) == 0
+
+    if not ignoreBackzone:
+        links = updateBackzoneLinks(tzdataDir, links)
+
+    generateTzDataLinkTestContent(
+        testDir,
+        version,
+        "timeZone_backward_links.js",
+        "// Link names derived from IANA Time Zone Database, backward file.",
+        links.items(),
+    )
+
+
+def generateTzDataTestNotBackwardLinks(tzdataDir, version, ignoreBackzone, testDir):
+    tzfiles = filterfalse(
+        {"backward", "backzone"}.__contains__, listIANAFiles(tzdataDir)
+    )
+    (zones, links) = readIANAFiles(tzdataDir, tzfiles)
+
+    if not ignoreBackzone:
+        links = updateBackzoneLinks(tzdataDir, links)
+
+    generateTzDataLinkTestContent(
+        testDir,
+        version,
+        "timeZone_notbackward_links.js",
+        "// Link names derived from IANA Time Zone Database, excluding backward file.",
+        links.items(),
+    )
+
+
+def generateTzDataTestBackzone(tzdataDir, version, ignoreBackzone, testDir):
+    backzoneFiles = {"backzone"}
+    (bkfiles, tzfiles) = partition(listIANAFiles(tzdataDir), backzoneFiles.__contains__)
+
+    # Read zone and link infos.
+    (zones, links) = readIANAFiles(tzdataDir, tzfiles)
+    (backzones, backlinks) = readIANAFiles(tzdataDir, bkfiles)
+
+    if not ignoreBackzone:
+        comment = """\
+// This file was generated with historical, pre-1970 backzone information
+// respected. Therefore, every zone key listed below is its own Zone, not
+// a Link to a modern-day target as IANA ignoring backzones would say.
+
+"""
+    else:
+        comment = """\
+// This file was generated while ignoring historical, pre-1970 backzone
+// information. Therefore, every zone key listed below is part of a Link
+// whose target is the corresponding value.
+
+"""
+
+    generateTzDataLinkTestContent(
+        testDir,
+        version,
+        "timeZone_backzone.js",
+        comment + "// Backzone zones derived from IANA Time Zone Database.",
+        (
+            (zone, zone if not ignoreBackzone else links[zone])
+            for zone in backzones
+            if zone in links
+        ),
+    )
+
+
+def generateTzDataTestBackzoneLinks(tzdataDir, version, ignoreBackzone, testDir):
+    backzoneFiles = {"backzone"}
+    (bkfiles, tzfiles) = partition(listIANAFiles(tzdataDir), backzoneFiles.__contains__)
+
+    # Read zone and link infos.
+    (zones, links) = readIANAFiles(tzdataDir, tzfiles)
+    (backzones, backlinks) = readIANAFiles(tzdataDir, bkfiles)
+
+    if not ignoreBackzone:
+        comment = """\
+// This file was generated with historical, pre-1970 backzone information
+// respected. Therefore, every zone key listed below points to a target
+// in the backzone file and not to its modern-day target as IANA ignoring
+// backzones would say.
+
+"""
+    else:
+        comment = """\
+// This file was generated while ignoring historical, pre-1970 backzone
+// information. Therefore, every zone key listed below is part of a Link
+// whose target is the corresponding value ignoring any backzone entries.
+
+"""
+
+    generateTzDataLinkTestContent(
+        testDir,
+        version,
+        "timeZone_backzone_links.js",
+        comment + "// Backzone links derived from IANA Time Zone Database.",
+        (
+            (zone, target if not ignoreBackzone else links[zone])
+            for (zone, target) in backlinks.items()
+        ),
+    )
+
+
+def generateTzDataTestVersion(tzdataDir, version, testDir):
+    fileName = "timeZone_version.js"
+
+    with io.open(
+        os.path.join(testDir, fileName), mode="w", encoding="utf-8", newline=""
+    ) as f:
+        println = partial(print, file=f)
+
+        println('// |reftest| skip-if(!this.hasOwnProperty("Intl"))')
+        println("")
+        println(generatedFileWarning)
+        println(tzdataVersionComment.format(version))
+        println("""const tzdata = "{0}";""".format(version))
+
+        println(
+            """
+if (typeof getICUOptions === "undefined") {
+    var getICUOptions = SpecialPowers.Cu.getJSTestingFunctions().getICUOptions;
+}
+
+var options = getICUOptions();
+
+assertEq(options.tzdata, tzdata);
+
+if (typeof reportCompare === "function")
+    reportCompare(0, 0, "ok");
+"""
+        )
+
+
+def generateTzDataTests(tzdataDir, version, ignoreBackzone, testDir):
+    generateTzDataTestBackwardLinks(tzdataDir, version, ignoreBackzone, testDir)
+    generateTzDataTestNotBackwardLinks(tzdataDir, version, ignoreBackzone, testDir)
+    generateTzDataTestBackzone(tzdataDir, version, ignoreBackzone, testDir)
+    generateTzDataTestBackzoneLinks(tzdataDir, version, ignoreBackzone, testDir)
+    generateTzDataTestVersion(tzdataDir, version, testDir)
+
+
+def updateTzdata(topsrcdir, args):
+    """ Update the time zone cpp file. """
+
+    icuDir = os.path.join(topsrcdir, "intl/icu/source")
+    if not os.path.isdir(icuDir):
+        raise RuntimeError("not a directory: %s" % icuDir)
+
+    icuTzDir = os.path.join(topsrcdir, "intl/tzdata/source")
+    if not os.path.isdir(icuTzDir):
+        raise RuntimeError("not a directory: %s" % icuTzDir)
+
+    dateTimeFormatTestDir = os.path.join(
+        topsrcdir, "js/src/tests/non262/Intl/DateTimeFormat"
+    )
+    if not os.path.isdir(dateTimeFormatTestDir):
+        raise RuntimeError("not a directory: %s" % dateTimeFormatTestDir)
+
+    tzDir = args.tz
+    if tzDir is not None and not (os.path.isdir(tzDir) or os.path.isfile(tzDir)):
+        raise RuntimeError("not a directory or file: %s" % tzDir)
+    ignoreBackzone = args.ignore_backzone
+    # TODO: Accept or ignore the placeholder time zone "Factory"?
+    ignoreFactory = False
+    out = args.out
+
+    version = icuTzDataVersion(icuTzDir)
+    url = (
+        "https://www.iana.org/time-zones/repository/releases/tzdata%s.tar.gz" % version
+    )
+
+    print("Arguments:")
+    print("\ttzdata version: %s" % version)
+    print("\ttzdata URL: %s" % url)
+    print("\ttzdata directory|file: %s" % tzDir)
+    print("\tICU directory: %s" % icuDir)
+    print("\tICU timezone directory: %s" % icuTzDir)
+    print("\tIgnore backzone file: %s" % ignoreBackzone)
+    print("\tOutput file: %s" % out)
+    print("")
+
+    def updateFrom(f):
+        if os.path.isfile(f) and tarfile.is_tarfile(f):
+            with tarfile.open(f, "r:*") as tar:
+                processTimeZones(
+                    TzDataFile(tar),
+                    icuDir,
+                    icuTzDir,
+                    version,
+                    ignoreBackzone,
+                    ignoreFactory,
+                    out,
+                )
+                generateTzDataTests(
+                    TzDataFile(tar), version, ignoreBackzone, dateTimeFormatTestDir
+                )
+        elif os.path.isdir(f):
+            processTimeZones(
+                TzDataDir(f),
+                icuDir,
+                icuTzDir,
+                version,
+                ignoreBackzone,
+                ignoreFactory,
+                out,
+            )
+            generateTzDataTests(
+                TzDataDir(f), version, ignoreBackzone, dateTimeFormatTestDir
+            )
+        else:
+            raise RuntimeError("unknown format")
+
+    if tzDir is None:
+        print("Downloading tzdata file...")
+        with closing(urlopen(url)) as tzfile:
+            fname = urlsplit(tzfile.geturl()).path.split("/")[-1]
+            with tempfile.NamedTemporaryFile(suffix=fname) as tztmpfile:
+                print("File stored in %s" % tztmpfile.name)
+                tztmpfile.write(tzfile.read())
+                tztmpfile.flush()
+                updateFrom(tztmpfile.name)
+    else:
+        updateFrom(tzDir)
+
+
+def readCurrencyFile(tree):
+    reCurrency = re.compile(r"^[A-Z]{3}$")
+    reIntMinorUnits = re.compile(r"^\d+$")
+
+    for country in tree.iterfind(".//CcyNtry"):
+        # Skip entry if no currency information is available.
+        currency = country.findtext("Ccy")
+        if currency is None:
+            continue
+        assert reCurrency.match(currency)
+
+        minorUnits = country.findtext("CcyMnrUnts")
+        assert minorUnits is not None
+
+        # Skip all entries without minorUnits or which use the default minorUnits.
+        if reIntMinorUnits.match(minorUnits) and int(minorUnits) != 2:
+            currencyName = country.findtext("CcyNm")
+            countryName = country.findtext("CtryNm")
+            yield (currency, int(minorUnits), currencyName, countryName)
+
+
+def writeCurrencyFile(published, currencies, out):
+    with io.open(out, mode="w", encoding="utf-8", newline="") as f:
+        println = partial(print, file=f)
+
+        println(generatedFileWarning)
+        println("// Version: {}".format(published))
+
+        println(
+            """
+/**
+ * Mapping from currency codes to the number of decimal digits used for them.
+ * Default is 2 digits.
+ *
+ * Spec: ISO 4217 Currency and Funds Code List.
+ * http://www.currency-iso.org/en/home/tables/table-a1.html
+ */"""
+        )
+        println("var currencyDigits = {")
+        for (currency, entries) in groupby(
+            sorted(currencies, key=itemgetter(0)), itemgetter(0)
+        ):
+            for (_, minorUnits, currencyName, countryName) in entries:
+                println("    // {} ({})".format(currencyName, countryName))
+            println("    {}: {},".format(currency, minorUnits))
+        println("};")
+
+
+def updateCurrency(topsrcdir, args):
+    """ Update the CurrencyDataGenerated.js file. """
+    import xml.etree.ElementTree as ET
+    from random import randint
+
+    url = args.url
+    out = args.out
+    filename = args.file
+
+    print("Arguments:")
+    print("\tDownload url: %s" % url)
+    print("\tLocal currency file: %s" % filename)
+    print("\tOutput file: %s" % out)
+    print("")
+
+    def updateFrom(currencyFile):
+        print("Processing currency code list file...")
+        tree = ET.parse(currencyFile)
+        published = tree.getroot().attrib["Pblshd"]
+        currencies = readCurrencyFile(tree)
+
+        print("Writing CurrencyData file...")
+        writeCurrencyFile(published, currencies, out)
+
+    if filename is not None:
+        print("Always make sure you have the newest currency code list file!")
+        updateFrom(filename)
+    else:
+        print("Downloading currency & funds code list...")
+        request = UrlRequest(url)
+        request.add_header(
+            "User-agent",
+            "Mozilla/5.0 (Mobile; rv:{0}.0) Gecko/{0}.0 Firefox/{0}.0".format(
+                randint(1, 999)
+            ),
+        )
+        with closing(urlopen(request)) as currencyFile:
+            fname = urlsplit(currencyFile.geturl()).path.split("/")[-1]
+            with tempfile.NamedTemporaryFile(suffix=fname) as currencyTmpFile:
+                print("File stored in %s" % currencyTmpFile.name)
+                currencyTmpFile.write(currencyFile.read())
+                currencyTmpFile.flush()
+                updateFrom(currencyTmpFile.name)
+
+
+def writeUnicodeExtensionsMappings(println, mapping, extension):
+    println(
+        """
+template <size_t Length>
+static inline bool Is{0}Key(
+  mozilla::Span<const char> key, const char (&str)[Length]) {{
+  static_assert(Length == {0}KeyLength + 1,
+                "{0} extension key is two characters long");
+  return memcmp(key.data(), str, Length - 1) == 0;
+}}
+
+template <size_t Length>
+static inline bool Is{0}Type(
+  mozilla::Span<const char> type, const char (&str)[Length]) {{
+  static_assert(Length > {0}KeyLength + 1,
+                "{0} extension type contains more than two characters");
+  return type.size() == (Length - 1) &&
+         memcmp(type.data(), str, Length - 1) == 0;
+}}
+""".format(
+            extension
+        ).rstrip(
+            "\n"
+        )
+    )
+
+    linear_search_max_length = 4
+
+    needs_binary_search = any(
+        len(replacements.items()) > linear_search_max_length
+        for replacements in mapping.values()
+    )
+
+    if needs_binary_search:
+        println(
+            """
+static int32_t Compare{0}Type(const char* a, mozilla::Span<const char> b) {{
+  MOZ_ASSERT(!std::char_traits<char>::find(b.data(), b.size(), '\\0'),
+             "unexpected null-character in string");
+
+  using UnsignedChar = unsigned char;
+  for (size_t i = 0; i < b.size(); i++) {{
+    // |a| is zero-terminated and |b| doesn't contain a null-terminator. So if
+    // we've reached the end of |a|, the below if-statement will always be true.
+    // That ensures we don't read past the end of |a|.
+    if (int32_t r = UnsignedChar(a[i]) - UnsignedChar(b[i])) {{
+      return r;
+    }}
+  }}
+
+  // Return zero if both strings are equal or a negative number if |b| is a
+  // prefix of |a|.
+  return -int32_t(UnsignedChar(a[b.size()]));
+}}
+
+template <size_t Length>
+static inline const char* Search{0}Replacement(
+  const char* (&types)[Length], const char* (&aliases)[Length],
+  mozilla::Span<const char> type) {{
+
+  auto p = std::lower_bound(std::begin(types), std::end(types), type,
+                            [](const auto& a, const auto& b) {{
+    return Compare{0}Type(a, b) < 0;
+  }});
+  if (p != std::end(types) && Compare{0}Type(*p, type) == 0) {{
+    return aliases[std::distance(std::begin(types), p)];
+  }}
+  return nullptr;
+}}
+""".format(
+                extension
+            ).rstrip(
+                "\n"
+            )
+        )
+
+    println(
+        """
+/**
+ * Mapping from deprecated BCP 47 {0} extension types to their preferred
+ * values.
+ *
+ * Spec: https://www.unicode.org/reports/tr35/#Unicode_Locale_Extension_Data_Files
+ * Spec: https://www.unicode.org/reports/tr35/#t_Extension
+ */
+const char* js::intl::LanguageTag::replace{0}ExtensionType(
+    mozilla::Span<const char> key, mozilla::Span<const char> type) {{
+  MOZ_ASSERT(key.size() == {0}KeyLength);
+  MOZ_ASSERT(IsCanonicallyCased{0}Key(key));
+
+  MOZ_ASSERT(type.size() > {0}KeyLength);
+  MOZ_ASSERT(IsCanonicallyCased{0}Type(type));
+""".format(
+            extension
+        )
+    )
+
+    def to_hash_key(replacements):
+        return str(sorted(replacements.items()))
+
+    def write_array(subtags, name, length):
+        max_entries = (80 - len("    ")) // (length + len('"", '))
+
+        println("    static const char* {}[{}] = {{".format(name, len(subtags)))
+
+        for entries in grouper(subtags, max_entries):
+            entries = (
+                '"{}"'.format(tag).rjust(length + 2)
+                for tag in entries
+                if tag is not None
+            )
+            println("      {},".format(", ".join(entries)))
+
+        println("    };")
+
+    # Merge duplicate keys.
+    key_aliases = {}
+    for (key, replacements) in sorted(mapping.items(), key=itemgetter(0)):
+        hash_key = to_hash_key(replacements)
+        if hash_key not in key_aliases:
+            key_aliases[hash_key] = []
+        else:
+            key_aliases[hash_key].append(key)
+
+    first_key = True
+    for (key, replacements) in sorted(mapping.items(), key=itemgetter(0)):
+        hash_key = to_hash_key(replacements)
+        if key in key_aliases[hash_key]:
+            continue
+
+        cond = (
+            'Is{}Key(key, "{}")'.format(extension, k)
+            for k in [key] + key_aliases[hash_key]
+        )
+
+        if_kind = "if" if first_key else "else if"
+        cond = (" ||\n" + " " * (2 + len(if_kind) + 2)).join(cond)
+        println(
+            """
+  {} ({}) {{""".format(
+                if_kind, cond
+            ).strip(
+                "\n"
+            )
+        )
+        first_key = False
+
+        replacements = sorted(replacements.items(), key=itemgetter(0))
+
+        if len(replacements) > linear_search_max_length:
+            types = [t for (t, _) in replacements]
+            preferred = [r for (_, r) in replacements]
+            max_len = max(len(k) for k in types + preferred)
+
+            write_array(types, "types", max_len)
+            write_array(preferred, "aliases", max_len)
+            println(
+                """
+    return Search{}Replacement(types, aliases, type);
+""".format(
+                    extension
+                ).strip(
+                    "\n"
+                )
+            )
+        else:
+            for (type, replacement) in replacements:
+                println(
+                    """
+    if (Is{}Type(type, "{}")) {{
+      return "{}";
+    }}""".format(
+                        extension, type, replacement
+                    ).strip(
+                        "\n"
+                    )
+                )
+
+        println(
+            """
+  }""".lstrip(
+                "\n"
+            )
+        )
+
+    println(
+        """
+  return nullptr;
+}
+""".strip(
+            "\n"
+        )
+    )
+
+
+def readICUUnitResourceFile(filepath):
+    """Return a set of unit descriptor pairs where the first entry denotes the unit type and the
+    second entry the unit name.
+
+    Example:
+
+    root{
+        units{
+            compound{
+            }
+            coordinate{
+            }
+            length{
+                meter{
+                }
+            }
+        }
+        unitsNarrow:alias{"/LOCALE/unitsShort"}
+        unitsShort{
+            duration{
+                day{
+                }
+                day-person:alias{"/LOCALE/unitsShort/duration/day"}
+            }
+            length{
+                meter{
+                }
+            }
+        }
+    }
+
+    Returns {("length", "meter"), ("duration", "day"), ("duration", "day-person")}
+    """
+
+    start_table_re = re.compile(r"^([\w\-%:\"]+)\{$")
+    end_table_re = re.compile(r"^\}$")
+    table_entry_re = re.compile(r"^([\w\-%:\"]+)\{\"(.*?)\"\}$")
+
+    # The current resource table.
+    table = {}
+
+    # List of parent tables when parsing.
+    parents = []
+
+    # Track multi-line comments state.
+    in_multiline_comment = False
+
+    for line in flines(filepath, "utf-8-sig"):
+        # Remove leading and trailing whitespace.
+        line = line.strip()
+
+        # Skip over comments.
+        if in_multiline_comment:
+            if line.endswith("*/"):
+                in_multiline_comment = False
+            continue
+
+        if line.startswith("//"):
+            continue
+
+        if line.startswith("/*"):
+            in_multiline_comment = True
+            continue
+
+        # Try to match the start of a table, e.g. `length{` or `meter{`.
+        match = start_table_re.match(line)
+        if match:
+            parents.append(table)
+            table_name = match.group(1)
+            new_table = {}
+            table[table_name] = new_table
+            table = new_table
+            continue
+
+        # Try to match the end of a table.
+        match = end_table_re.match(line)
+        if match:
+            table = parents.pop()
+            continue
+
+        # Try to match a table entry, e.g. `dnam{"meter"}`.
+        match = table_entry_re.match(line)
+        if match:
+            entry_key = match.group(1)
+            entry_value = match.group(2)
+            table[entry_key] = entry_value
+            continue
+
+        raise Exception("unexpected line: '{}' in {}".format(line, filepath))
+
+    assert len(parents) == 0, "Not all tables closed"
+    assert len(table) == 1, "More than one root table"
+
+    # Remove the top-level language identifier table.
+    (_, unit_table) = table.popitem()
+
+    # Add all units for the three display formats "units", "unitsNarrow", and "unitsShort".
+    # But exclude the pseudo-units "compound" and "ccoordinate".
+    return {
+        (unit_type, unit_name if not unit_name.endswith(":alias") else unit_name[:-6])
+        for unit_display in ("units", "unitsNarrow", "unitsShort")
+        if unit_display in unit_table
+        for (unit_type, unit_names) in unit_table[unit_display].items()
+        if unit_type != "compound" and unit_type != "coordinate"
+        for unit_name in unit_names.keys()
+    }
+
+
+def computeSupportedUnits(all_units, sanctioned_units):
+    """Given the set of all possible ICU unit identifiers and the set of sanctioned unit
+    identifiers, compute the set of effectively supported ICU unit identifiers.
+    """
+
+    def find_match(unit):
+        unit_match = [
+            (unit_type, unit_name)
+            for (unit_type, unit_name) in all_units
+            if unit_name == unit
+        ]
+        if unit_match:
+            assert len(unit_match) == 1
+            return unit_match[0]
+        return None
+
+    def compound_unit_identifiers():
+        for numerator in sanctioned_units:
+            for denominator in sanctioned_units:
+                yield "{}-per-{}".format(numerator, denominator)
+
+    supported_simple_units = {find_match(unit) for unit in sanctioned_units}
+    assert None not in supported_simple_units
+
+    supported_compound_units = {
+        unit_match
+        for unit_match in (find_match(unit) for unit in compound_unit_identifiers())
+        if unit_match
+    }
+
+    return supported_simple_units | supported_compound_units
+
+
+def readICUDataFilterForUnits(data_filter_file):
+    with io.open(data_filter_file, mode="r", encoding="utf-8") as f:
+        data_filter = json.load(f)
+
+    # Find the rule set for the "unit_tree".
+    unit_tree_rules = [
+        entry["rules"]
+        for entry in data_filter["resourceFilters"]
+        if entry["categories"] == ["unit_tree"]
+    ]
+    assert len(unit_tree_rules) == 1
+
+    # Compute the list of included units from that rule set. The regular expression must match
+    # "+/*/length/meter" and mustn't match either "-/*" or "+/*/compound".
+    included_unit_re = re.compile(r"^\+/\*/(.+?)/(.+)$")
+    filtered_units = (included_unit_re.match(unit) for unit in unit_tree_rules[0])
+
+    return {(unit.group(1), unit.group(2)) for unit in filtered_units if unit}
+
+
+def writeSanctionedSimpleUnitIdentifiersFiles(all_units, sanctioned_units):
+    js_src_builtin_intl_dir = os.path.dirname(os.path.abspath(__file__))
+
+    def find_unit_type(unit):
+        result = [
+            unit_type for (unit_type, unit_name) in all_units if unit_name == unit
+        ]
+        assert result and len(result) == 1
+        return result[0]
+
+    sanctioned_js_file = os.path.join(
+        js_src_builtin_intl_dir, "SanctionedSimpleUnitIdentifiersGenerated.js"
+    )
+    with io.open(sanctioned_js_file, mode="w", encoding="utf-8", newline="") as f:
+        println = partial(print, file=f)
+
+        sanctioned_units_object = json.dumps(
+            {unit: True for unit in sorted(sanctioned_units)},
+            sort_keys=True,
+            indent=4,
+            separators=(",", ": "),
+        )
+
+        println(generatedFileWarning)
+
+        println(
+            """
+/**
+ * The list of currently supported simple unit identifiers.
+ *
+ * Intl.NumberFormat Unified API Proposal
+ */"""
+        )
+
+        println(
+            "var sanctionedSimpleUnitIdentifiers = {};".format(sanctioned_units_object)
+        )
+
+    sanctioned_cpp_file = os.path.join(
+        js_src_builtin_intl_dir, "MeasureUnitGenerated.h"
+    )
+    with io.open(sanctioned_cpp_file, mode="w", encoding="utf-8", newline="") as f:
+        println = partial(print, file=f)
+
+        println(generatedFileWarning)
+
+        println(
+            """
+struct MeasureUnit {
+  const char* const type;
+  const char* const name;
+};
+
+/**
+ * The list of currently supported simple unit identifiers.
+ *
+ * The list must be kept in alphabetical order of |name|.
+ */
+inline constexpr MeasureUnit simpleMeasureUnits[] = {
+    // clang-format off"""
+        )
+
+        for unit_name in sorted(sanctioned_units):
+            println('  {{"{}", "{}"}},'.format(find_unit_type(unit_name), unit_name))
+
+        println(
+            """
+    // clang-format on
+};""".lstrip(
+                "\n"
+            )
+        )
+
+    writeUnitTestFiles(all_units, sanctioned_units)
+
+
+def writeUnitTestFiles(all_units, sanctioned_units):
+    """ Generate test files for unit number formatters. """
+
+    js_src_builtin_intl_dir = os.path.dirname(os.path.abspath(__file__))
+    test_dir = os.path.join(
+        js_src_builtin_intl_dir, "../../tests/non262/Intl/NumberFormat"
+    )
+
+    def write_test(file_name, test_content, indent=4):
+        file_path = os.path.join(test_dir, file_name)
+        with io.open(file_path, mode="w", encoding="utf-8", newline="") as f:
+            println = partial(print, file=f)
+
+            println('// |reftest| skip-if(!this.hasOwnProperty("Intl"))')
+            println("")
+            println(generatedFileWarning)
+            println("")
+
+            sanctioned_units_array = json.dumps(
+                [unit for unit in sorted(sanctioned_units)],
+                indent=indent,
+                separators=(",", ": "),
+            )
+
+            println(
+                "const sanctionedSimpleUnitIdentifiers = {};".format(
+                    sanctioned_units_array
+                )
+            )
+
+            println(test_content)
+
+            println(
+                """
+if (typeof reportCompare === "function")
+{}reportCompare(true, true);""".format(
+                    " " * indent
+                )
+            )
+
+    write_test(
+        "unit-compound-combinations.js",
+        """
+// Test all simple unit identifier combinations are allowed.
+
+for (const numerator of sanctionedSimpleUnitIdentifiers) {
+    for (const denominator of sanctionedSimpleUnitIdentifiers) {
+        const unit = `${numerator}-per-${denominator}`;
+        const nf = new Intl.NumberFormat("en", {style: "unit", unit});
+
+        assertEq(nf.format(1), nf.formatToParts(1).map(p => p.value).join(""));
+    }
+}""",
+    )
+
+    all_units_array = json.dumps(
+        ["-".join(unit) for unit in sorted(all_units)], indent=4, separators=(",", ": ")
+    )
+
+    write_test(
+        "unit-well-formed.js",
+        """
+const allUnits = {};
+""".format(
+            all_units_array
+        )
+        + """
+// Test only sanctioned unit identifiers are allowed.
+
+for (const typeAndUnit of allUnits) {
+    const [_, type, unit] = typeAndUnit.match(/(\w+)-(.+)/);
+
+    let allowed;
+    if (unit.includes("-per-")) {
+        const [numerator, denominator] = unit.split("-per-");
+        allowed = sanctionedSimpleUnitIdentifiers.includes(numerator) &&
+                  sanctionedSimpleUnitIdentifiers.includes(denominator);
+    } else {
+        allowed = sanctionedSimpleUnitIdentifiers.includes(unit);
+    }
+
+    if (allowed) {
+        const nf = new Intl.NumberFormat("en", {style: "unit", unit});
+        assertEq(nf.format(1), nf.formatToParts(1).map(p => p.value).join(""));
+    } else {
+        assertThrowsInstanceOf(() => new Intl.NumberFormat("en", {style: "unit", unit}),
+                               RangeError, `Missing error for "${typeAndUnit}"`);
+    }
+}""",
+    )
+
+    write_test(
+        "unit-formatToParts-has-unit-field.js",
+        """
+// Test only English and Chinese to keep the overall runtime reasonable.
+//
+// Chinese is included because it contains more than one "unit" element for
+// certain unit combinations.
+const locales = ["en", "zh"];
+
+// Plural rules for English only differentiate between "one" and "other". Plural
+// rules for Chinese only use "other". That means we only need to test two values
+// per unit.
+const values = [0, 1];
+
+// Ensure unit formatters contain at least one "unit" element.
+
+for (const locale of locales) {
+  for (const unit of sanctionedSimpleUnitIdentifiers) {
+    const nf = new Intl.NumberFormat(locale, {style: "unit", unit});
+
+    for (const value of values) {
+      assertEq(nf.formatToParts(value).some(e => e.type === "unit"), true,
+               `locale=${locale}, unit=${unit}`);
+    }
+  }
+
+  for (const numerator of sanctionedSimpleUnitIdentifiers) {
+    for (const denominator of sanctionedSimpleUnitIdentifiers) {
+      const unit = `${numerator}-per-${denominator}`;
+      const nf = new Intl.NumberFormat(locale, {style: "unit", unit});
+
+      for (const value of values) {
+        assertEq(nf.formatToParts(value).some(e => e.type === "unit"), true,
+                 `locale=${locale}, unit=${unit}`);
+      }
+    }
+  }
+}""",
+        indent=2,
+    )
+
+
+def updateUnits(topsrcdir, args):
+    icu_path = os.path.join(topsrcdir, "intl", "icu")
+    icu_unit_path = os.path.join(icu_path, "source", "data", "unit")
+
+    with io.open(
+        "SanctionedSimpleUnitIdentifiers.yaml", mode="r", encoding="utf-8"
+    ) as f:
+        sanctioned_units = yaml.safe_load(f)
+
+    # Read all possible ICU unit identifiers from the "unit/root.txt" resource.
+    unit_root_file = os.path.join(icu_unit_path, "root.txt")
+    all_units = readICUUnitResourceFile(unit_root_file)
+
+    # Compute the set of effectively supported ICU unit identifiers.
+    supported_units = computeSupportedUnits(all_units, sanctioned_units)
+
+    # Read the list of units we're including into the ICU data file.
+    data_filter_file = os.path.join(icu_path, "data_filter.json")
+    filtered_units = readICUDataFilterForUnits(data_filter_file)
+
+    # Both sets must match to avoid resource loading errors at runtime.
+    if supported_units != filtered_units:
+
+        def units_to_string(units):
+            return ", ".join("/".join(u) for u in units)
+
+        missing = supported_units - filtered_units
+        if missing:
+            raise RuntimeError("Missing units: {}".format(units_to_string(missing)))
+
+        # Not exactly an error, but we currently don't have a use case where we need to support
+        # more units than required by ECMA-402.
+        extra = filtered_units - supported_units
+        if extra:
+            raise RuntimeError("Unnecessary units: {}".format(units_to_string(extra)))
+
+    writeSanctionedSimpleUnitIdentifiersFiles(all_units, sanctioned_units)
+
+
+def readICUNumberingSystemsResourceFile(filepath):
+    """Returns a dictionary of numbering systems where the key denotes the numbering system name
+    and the value a dictionary with additional numbering system data.
+
+    Example:
+
+    numberingSystems:table(nofallback){
+        numberingSystems{
+            latn{
+                algorithmic:int{0}
+                desc{"0123456789"}
+                radix:int{10}
+            }
+            roman{
+                algorithmic:int{1}
+                desc{"%roman-upper"}
+                radix:int{10}
+            }
+        }
+    }
+
+    Returns {"latn": {"digits": "0123456789", "algorithmic": False},
+             "roman": {"algorithmic": True}}
+    """
+
+    start_table_re = re.compile(r"^(\w+)(?:\:[\w\(\)]+)?\{$")
+    end_table_re = re.compile(r"^\}$")
+    table_entry_re = re.compile(r"^(\w+)(?:\:[\w\(\)]+)?\{(?:(?:\"(.*?)\")|(\d+))\}$")
+
+    # The current resource table.
+    table = {}
+
+    # List of parent tables when parsing.
+    parents = []
+
+    # Track multi-line comments state.
+    in_multiline_comment = False
+
+    for line in flines(filepath, "utf-8-sig"):
+        # Remove leading and trailing whitespace.
+        line = line.strip()
+
+        # Skip over comments.
+        if in_multiline_comment:
+            if line.endswith("*/"):
+                in_multiline_comment = False
+            continue
+
+        if line.startswith("//"):
+            continue
+
+        if line.startswith("/*"):
+            in_multiline_comment = True
+            continue
+
+        # Try to match the start of a table, e.g. `latn{`.
+        match = start_table_re.match(line)
+        if match:
+            parents.append(table)
+            table_name = match.group(1)
+            new_table = {}
+            table[table_name] = new_table
+            table = new_table
+            continue
+
+        # Try to match the end of a table.
+        match = end_table_re.match(line)
+        if match:
+            table = parents.pop()
+            continue
+
+        # Try to match a table entry, e.g. `desc{"0123456789"}`.
+        match = table_entry_re.match(line)
+        if match:
+            entry_key = match.group(1)
+            entry_value = (
+                match.group(2) if match.group(2) is not None else int(match.group(3))
+            )
+            table[entry_key] = entry_value
+            continue
+
+        raise Exception("unexpected line: '{}' in {}".format(line, filepath))
+
+    assert len(parents) == 0, "Not all tables closed"
+    assert len(table) == 1, "More than one root table"
+
+    # Remove the two top-level "numberingSystems" tables.
+    (_, numbering_systems) = table.popitem()
+    (_, numbering_systems) = numbering_systems.popitem()
+
+    # Assert all numbering systems use base 10.
+    assert all(ns["radix"] == 10 for ns in numbering_systems.values())
+
+    # Return the numbering systems.
+    return {
+        key: {"digits": value["desc"], "algorithmic": False}
+        if not bool(value["algorithmic"])
+        else {"algorithmic": True}
+        for (key, value) in numbering_systems.items()
+    }
+
+
+def writeNumberingSystemFiles(numbering_systems):
+    js_src_builtin_intl_dir = os.path.dirname(os.path.abspath(__file__))
+
+    numbering_systems_js_file = os.path.join(
+        js_src_builtin_intl_dir, "NumberingSystemsGenerated.h"
+    )
+    with io.open(
+        numbering_systems_js_file, mode="w", encoding="utf-8", newline=""
+    ) as f:
+        println = partial(print, file=f)
+
+        println(generatedFileWarning)
+
+        println(
+            """
+/**
+ * The list of numbering systems with simple digit mappings.
+ */
+
+#ifndef builtin_intl_NumberingSystemsGenerated_h
+#define builtin_intl_NumberingSystemsGenerated_h
+"""
+        )
+
+        simple_numbering_systems = sorted(
+            name
+            for (name, value) in numbering_systems.items()
+            if not value["algorithmic"]
+        )
+
+        println("// clang-format off")
+        println("#define NUMBERING_SYSTEMS_WITH_SIMPLE_DIGIT_MAPPINGS \\")
+        println(
+            "{}".format(
+                ", \\\n".join(
+                    '  "{}"'.format(name) for name in simple_numbering_systems
+                )
+            )
+        )
+        println("// clang-format on")
+        println("")
+
+        println("#endif  // builtin_intl_NumberingSystemsGenerated_h")
+
+    js_src_builtin_intl_dir = os.path.dirname(os.path.abspath(__file__))
+    test_dir = os.path.join(js_src_builtin_intl_dir, "../../tests/non262/Intl")
+
+    intl_shell_js_file = os.path.join(test_dir, "shell.js")
+
+    with io.open(intl_shell_js_file, mode="w", encoding="utf-8", newline="") as f:
+        println = partial(print, file=f)
+
+        println(generatedFileWarning)
+
+        println(
+            """
+// source: CLDR file common/bcp47/number.xml; version CLDR {}.
+// https://github.com/unicode-org/cldr/blob/master/common/bcp47/number.xml
+// https://github.com/unicode-org/cldr/blob/master/common/supplemental/numberingSystems.xml
+""".format(
+                readCLDRVersionFromICU()
+            ).rstrip()
+        )
+
+        numbering_systems_object = json.dumps(
+            numbering_systems,
+            indent=2,
+            separators=(",", ": "),
+            sort_keys=True,
+            ensure_ascii=False,
+        )
+        println("const numberingSystems = {};".format(numbering_systems_object))
+
+
+def updateNumberingSystems(topsrcdir, args):
+    icu_path = os.path.join(topsrcdir, "intl", "icu")
+    icu_misc_path = os.path.join(icu_path, "source", "data", "misc")
+
+    with io.open("NumberingSystems.yaml", mode="r", encoding="utf-8") as f:
+        numbering_systems = yaml.safe_load(f)
+
+    # Read all possible ICU unit identifiers from the "misc/numberingSystems.txt" resource.
+    misc_ns_file = os.path.join(icu_misc_path, "numberingSystems.txt")
+    all_numbering_systems = readICUNumberingSystemsResourceFile(misc_ns_file)
+
+    all_numbering_systems_simple_digits = {
+        name
+        for (name, value) in all_numbering_systems.items()
+        if not value["algorithmic"]
+    }
+
+    # Assert ICU includes support for all required numbering systems. If this assertion fails,
+    # something is broken in ICU.
+    assert all_numbering_systems_simple_digits.issuperset(
+        numbering_systems
+    ), "{}".format(numbering_systems.difference(all_numbering_systems_simple_digits))
+
+    # Assert the spec requires support for all numbering systems with simple digit mappings. If
+    # this assertion fails, file a PR at <https://github.com/tc39/ecma402> to include any new
+    # numbering systems.
+    assert all_numbering_systems_simple_digits.issubset(numbering_systems), "{}".format(
+        all_numbering_systems_simple_digits.difference(numbering_systems)
+    )
+
+    writeNumberingSystemFiles(all_numbering_systems)
+
+
+if __name__ == "__main__":
+    import argparse
+
+    # This script must reside in js/src/builtin/intl to work correctly.
+    (thisDir, thisFile) = os.path.split(os.path.abspath(sys.argv[0]))
+    dirPaths = os.path.normpath(thisDir).split(os.sep)
+    if "/".join(dirPaths[-4:]) != "js/src/builtin/intl":
+        raise RuntimeError("%s must reside in js/src/builtin/intl" % sys.argv[0])
+    topsrcdir = "/".join(dirPaths[:-4])
+
+    def EnsureHttps(v):
+        if not v.startswith("https:"):
+            raise argparse.ArgumentTypeError("URL protocol must be https: " % v)
+        return v
+
+    parser = argparse.ArgumentParser(description="Update intl data.")
+    subparsers = parser.add_subparsers(help="Select update mode")
+
+    parser_cldr_tags = subparsers.add_parser(
+        "langtags", help="Update CLDR language tags data"
+    )
+    parser_cldr_tags.add_argument(
+        "--version", metavar="VERSION", help="CLDR version number"
+    )
+    parser_cldr_tags.add_argument(
+        "--url",
+        metavar="URL",
+        default="https://unicode.org/Public/cldr/<VERSION>/core.zip",
+        type=EnsureHttps,
+        help="Download url CLDR data (default: %(default)s)",
+    )
+    parser_cldr_tags.add_argument(
+        "--out",
+        default="LanguageTagGenerated.cpp",
+        help="Output file (default: %(default)s)",
+    )
+    parser_cldr_tags.add_argument(
+        "file", nargs="?", help="Local cldr-core.zip file, if omitted uses <URL>"
+    )
+    parser_cldr_tags.set_defaults(func=updateCLDRLangTags)
+
+    parser_tz = subparsers.add_parser("tzdata", help="Update tzdata")
+    parser_tz.add_argument(
+        "--tz",
+        help="Local tzdata directory or file, if omitted downloads tzdata "
+        "distribution from https://www.iana.org/time-zones/",
+    )
+    # ICU doesn't include the backzone file by default, but we still like to
+    # use the backzone time zone names to avoid user confusion. This does lead
+    # to formatting "historic" dates (pre-1970 era) with the wrong time zone,
+    # but that's probably acceptable for now.
+    parser_tz.add_argument(
+        "--ignore-backzone",
+        action="store_true",
+        help="Ignore tzdata's 'backzone' file. Can be enabled to generate more "
+        "accurate time zone canonicalization reflecting the actual time "
+        "zones as used by ICU.",
+    )
+    parser_tz.add_argument(
+        "--out",
+        default="TimeZoneDataGenerated.h",
+        help="Output file (default: %(default)s)",
+    )
+    parser_tz.set_defaults(func=partial(updateTzdata, topsrcdir))
+
+    parser_currency = subparsers.add_parser(
+        "currency", help="Update currency digits mapping"
+    )
+    parser_currency.add_argument(
+        "--url",
+        metavar="URL",
+        default="https://www.currency-iso.org/dam/downloads/lists/list_one.xml",  # NOQA: E501
+        type=EnsureHttps,
+        help="Download url for the currency & funds code list (default: "
+        "%(default)s)",
+    )
+    parser_currency.add_argument(
+        "--out",
+        default="CurrencyDataGenerated.js",
+        help="Output file (default: %(default)s)",
+    )
+    parser_currency.add_argument(
+        "file", nargs="?", help="Local currency code list file, if omitted uses <URL>"
+    )
+    parser_currency.set_defaults(func=partial(updateCurrency, topsrcdir))
+
+    parser_units = subparsers.add_parser(
+        "units", help="Update sanctioned unit identifiers mapping"
+    )
+    parser_units.set_defaults(func=partial(updateUnits, topsrcdir))
+
+    parser_numbering_systems = subparsers.add_parser(
+        "numbering", help="Update numbering systems with simple " "digit mappings"
+    )
+    parser_numbering_systems.set_defaults(
+        func=partial(updateNumberingSystems, topsrcdir)
+    )
+
+    args = parser.parse_args()
+    args.func(args)