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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:generate go run gen.go -output tables.go
package language
// TODO: Remove above NOTE after:
// - verifying that tables are dropped correctly (most notably matcher tables).
import (
// Tag represents a BCP 47 language tag. It is used to specify an instance of a
// specific language or locale. All language tag values are guaranteed to be
// well-formed.
type Tag compact.Tag
func makeTag(t language.Tag) (tag Tag) {
return Tag(compact.Make(t))
func (t *Tag) tag() language.Tag {
return (*compact.Tag)(t).Tag()
func (t *Tag) isCompact() bool {
return (*compact.Tag)(t).IsCompact()
// TODO: improve performance.
func (t *Tag) lang() language.Language { return t.tag().LangID }
func (t *Tag) region() language.Region { return t.tag().RegionID }
func (t *Tag) script() language.Script { return t.tag().ScriptID }
// Make is a convenience wrapper for Parse that omits the error.
// In case of an error, a sensible default is returned.
func Make(s string) Tag {
return Default.Make(s)
// Make is a convenience wrapper for c.Parse that omits the error.
// In case of an error, a sensible default is returned.
func (c CanonType) Make(s string) Tag {
t, _ := c.Parse(s)
return t
// Raw returns the raw base language, script and region, without making an
// attempt to infer their values.
func (t Tag) Raw() (b Base, s Script, r Region) {
tt := t.tag()
return Base{tt.LangID}, Script{tt.ScriptID}, Region{tt.RegionID}
// IsRoot returns true if t is equal to language "und".
func (t Tag) IsRoot() bool {
return compact.Tag(t).IsRoot()
// CanonType can be used to enable or disable various types of canonicalization.
type CanonType int
const (
// Replace deprecated base languages with their preferred replacements.
DeprecatedBase CanonType = 1 << iota
// Replace deprecated scripts with their preferred replacements.
// Replace deprecated regions with their preferred replacements.
// Remove redundant scripts.
// Normalize legacy encodings. This includes legacy languages defined in
// CLDR as well as bibliographic codes defined in ISO-639.
// Map the dominant language of a macro language group to the macro language
// subtag. For example cmn -> zh.
// The CLDR flag should be used if full compatibility with CLDR is required.
// There are a few cases where language.Tag may differ from CLDR. To follow all
// of CLDR's suggestions, use All|CLDR.
// Raw can be used to Compose or Parse without Canonicalization.
Raw CanonType = 0
// Replace all deprecated tags with their preferred replacements.
Deprecated = DeprecatedBase | DeprecatedScript | DeprecatedRegion
// All canonicalizations recommended by BCP 47.
BCP47 = Deprecated | SuppressScript
// All canonicalizations.
All = BCP47 | Legacy | Macro
// Default is the canonicalization used by Parse, Make and Compose. To
// preserve as much information as possible, canonicalizations that remove
// potentially valuable information are not included. The Matcher is
// designed to recognize similar tags that would be the same if
// they were canonicalized using All.
Default = Deprecated | Legacy
canonLang = DeprecatedBase | Legacy | Macro
// TODO: LikelyScript, LikelyRegion: suppress similar to ICU.
// canonicalize returns the canonicalized equivalent of the tag and
// whether there was any change.
func canonicalize(c CanonType, t language.Tag) (language.Tag, bool) {
if c == Raw {
return t, false
changed := false
if c&SuppressScript != 0 {
if t.LangID.SuppressScript() == t.ScriptID {
t.ScriptID = 0
changed = true
if c&canonLang != 0 {
for {
if l, aliasType := t.LangID.Canonicalize(); l != t.LangID {
switch aliasType {
case language.Legacy:
if c&Legacy != 0 {
if t.LangID == _sh && t.ScriptID == 0 {
t.ScriptID = _Latn
t.LangID = l
changed = true
case language.Macro:
if c&Macro != 0 {
// We deviate here from CLDR. The mapping "nb" -> "no"
// qualifies as a typical Macro language mapping. However,
// for legacy reasons, CLDR maps "no", the macro language
// code for Norwegian, to the dominant variant "nb". This
// change is currently under consideration for CLDR as well.
// See and also
// for some of the
// practical implications. TODO: this check could be removed
// if CLDR adopts this change.
if c&CLDR == 0 || t.LangID != _nb {
changed = true
t.LangID = l
case language.Deprecated:
if c&DeprecatedBase != 0 {
if t.LangID == _mo && t.RegionID == 0 {
t.RegionID = _MD
t.LangID = l
changed = true
// Other canonicalization types may still apply.
} else if c&Legacy != 0 && t.LangID == _no && c&CLDR != 0 {
t.LangID = _nb
changed = true
if c&DeprecatedScript != 0 {
if t.ScriptID == _Qaai {
changed = true
t.ScriptID = _Zinh
if c&DeprecatedRegion != 0 {
if r := t.RegionID.Canonicalize(); r != t.RegionID {
changed = true
t.RegionID = r
return t, changed
// Canonicalize returns the canonicalized equivalent of the tag.
func (c CanonType) Canonicalize(t Tag) (Tag, error) {
// First try fast path.
if t.isCompact() {
if _, changed := canonicalize(c, compact.Tag(t).Tag()); !changed {
return t, nil
// It is unlikely that one will canonicalize a tag after matching. So do
// a slow but simple approach here.
if tag, changed := canonicalize(c, t.tag()); changed {
return makeTag(tag), nil
return t, nil
// Confidence indicates the level of certainty for a given return value.
// For example, Serbian may be written in Cyrillic or Latin script.
// The confidence level indicates whether a value was explicitly specified,
// whether it is typically the only possible value, or whether there is
// an ambiguity.
type Confidence int
const (
No Confidence = iota // full confidence that there was no match
Low // most likely value picked out of a set of alternatives
High // value is generally assumed to be the correct match
Exact // exact match or explicitly specified value
var confName = []string{"No", "Low", "High", "Exact"}
func (c Confidence) String() string {
return confName[c]
// String returns the canonical string representation of the language tag.
func (t Tag) String() string {
return t.tag().String()
// MarshalText implements encoding.TextMarshaler.
func (t Tag) MarshalText() (text []byte, err error) {
return t.tag().MarshalText()
// UnmarshalText implements encoding.TextUnmarshaler.
func (t *Tag) UnmarshalText(text []byte) error {
var tag language.Tag
err := tag.UnmarshalText(text)
*t = makeTag(tag)
return err
// Base returns the base language of the language tag. If the base language is
// unspecified, an attempt will be made to infer it from the context.
// It uses a variant of CLDR's Add Likely Subtags algorithm. This is subject to change.
func (t Tag) Base() (Base, Confidence) {
if b := t.lang(); b != 0 {
return Base{b}, Exact
tt := t.tag()
c := High
if tt.ScriptID == 0 && !tt.RegionID.IsCountry() {
c = Low
if tag, err := tt.Maximize(); err == nil && tag.LangID != 0 {
return Base{tag.LangID}, c
return Base{0}, No
// Script infers the script for the language tag. If it was not explicitly given, it will infer
// a most likely candidate.
// If more than one script is commonly used for a language, the most likely one
// is returned with a low confidence indication. For example, it returns (Cyrl, Low)
// for Serbian.
// If a script cannot be inferred (Zzzz, No) is returned. We do not use Zyyy (undetermined)
// as one would suspect from the IANA registry for BCP 47. In a Unicode context Zyyy marks
// common characters (like 1, 2, 3, '.', etc.) and is therefore more like multiple scripts.
// See for more details. Zzzz is also used for
// unknown value in CLDR. (Zzzz, Exact) is returned if Zzzz was explicitly specified.
// Note that an inferred script is never guaranteed to be the correct one. Latin is
// almost exclusively used for Afrikaans, but Arabic has been used for some texts
// in the past. Also, the script that is commonly used may change over time.
// It uses a variant of CLDR's Add Likely Subtags algorithm. This is subject to change.
func (t Tag) Script() (Script, Confidence) {
if scr := t.script(); scr != 0 {
return Script{scr}, Exact
tt := t.tag()
sc, c := language.Script(_Zzzz), No
if scr := tt.LangID.SuppressScript(); scr != 0 {
// Note: it is not always the case that a language with a suppress
// script value is only written in one script (e.g. kk, ms, pa).
if tt.RegionID == 0 {
return Script{scr}, High
sc, c = scr, High
if tag, err := tt.Maximize(); err == nil {
if tag.ScriptID != sc {
sc, c = tag.ScriptID, Low
} else {
tt, _ = canonicalize(Deprecated|Macro, tt)
if tag, err := tt.Maximize(); err == nil && tag.ScriptID != sc {
sc, c = tag.ScriptID, Low
return Script{sc}, c
// Region returns the region for the language tag. If it was not explicitly given, it will
// infer a most likely candidate from the context.
// It uses a variant of CLDR's Add Likely Subtags algorithm. This is subject to change.
func (t Tag) Region() (Region, Confidence) {
if r := t.region(); r != 0 {
return Region{r}, Exact
tt := t.tag()
if tt, err := tt.Maximize(); err == nil {
return Region{tt.RegionID}, Low // TODO: differentiate between high and low.
tt, _ = canonicalize(Deprecated|Macro, tt)
if tag, err := tt.Maximize(); err == nil {
return Region{tag.RegionID}, Low
return Region{_ZZ}, No // TODO: return world instead of undetermined?
// Variants returns the variants specified explicitly for this language tag.
// or nil if no variant was specified.
func (t Tag) Variants() []Variant {
if !compact.Tag(t).MayHaveVariants() {
return nil
v := []Variant{}
x, str := "", t.tag().Variants()
for str != "" {
x, str = nextToken(str)
v = append(v, Variant{x})
return v
// Parent returns the CLDR parent of t. In CLDR, missing fields in data for a
// specific language are substituted with fields from the parent language.
// The parent for a language may change for newer versions of CLDR.
func (t Tag) Parent() Tag {
return Tag(compact.Tag(t).Parent())
// returns token t and the rest of the string.
func nextToken(s string) (t, tail string) {
p := strings.Index(s[1:], "-")
if p == -1 {
return s[1:], ""
return s[1:p], s[p:]
// Extension is a single BCP 47 extension.
type Extension struct {
s string
// String returns the string representation of the extension, including the
// type tag.
func (e Extension) String() string {
return e.s
// ParseExtension parses s as an extension and returns it on success.
func ParseExtension(s string) (e Extension, err error) {
ext, err := language.ParseExtension(s)
return Extension{ext}, err
// Type returns the one-byte extension type of e. It returns 0 for the zero
// exception.
func (e Extension) Type() byte {
if e.s == "" {
return 0
return e.s[0]
// Tokens returns the list of tokens of e.
func (e Extension) Tokens() []string {
return strings.Split(e.s, "-")
// Extension returns the extension of type x for tag t. It will return
// false for ok if t does not have the requested extension. The returned
// extension will be invalid in this case.
func (t Tag) Extension(x byte) (ext Extension, ok bool) {
if !compact.Tag(t).MayHaveExtensions() {
return Extension{}, false
e, ok := t.tag().Extension(x)
return Extension{e}, ok
// Extensions returns all extensions of t.
func (t Tag) Extensions() []Extension {
if !compact.Tag(t).MayHaveExtensions() {
return nil
e := []Extension{}
for _, ext := range t.tag().Extensions() {
e = append(e, Extension{ext})
return e
// TypeForKey returns the type associated with the given key, where key and type
// are of the allowed values defined for the Unicode locale extension ('u') in
// TypeForKey will traverse the inheritance chain to get the correct value.
func (t Tag) TypeForKey(key string) string {
if !compact.Tag(t).MayHaveExtensions() {
if key != "rg" && key != "va" {
return ""
return t.tag().TypeForKey(key)
// SetTypeForKey returns a new Tag with the key set to type, where key and type
// are of the allowed values defined for the Unicode locale extension ('u') in
// An empty value removes an existing pair with the same key.
func (t Tag) SetTypeForKey(key, value string) (Tag, error) {
tt, err := t.tag().SetTypeForKey(key, value)
return makeTag(tt), err
// NumCompactTags is the number of compact tags. The maximum tag is
// NumCompactTags-1.
const NumCompactTags = compact.NumCompactTags
// CompactIndex returns an index, where 0 <= index < NumCompactTags, for tags
// for which data exists in the text repository.The index will change over time
// and should not be stored in persistent storage. If t does not match a compact
// index, exact will be false and the compact index will be returned for the
// first match after repeatedly taking the Parent of t.
func CompactIndex(t Tag) (index int, exact bool) {
id, exact := compact.LanguageID(compact.Tag(t))
return int(id), exact
var root = language.Tag{}
// Base is an ISO 639 language code, used for encoding the base language
// of a language tag.
type Base struct {
langID language.Language
// ParseBase parses a 2- or 3-letter ISO 639 code.
// It returns a ValueError if s is a well-formed but unknown language identifier
// or another error if another error occurred.
func ParseBase(s string) (Base, error) {
l, err := language.ParseBase(s)
return Base{l}, err
// String returns the BCP 47 representation of the base language.
func (b Base) String() string {
return b.langID.String()
// ISO3 returns the ISO 639-3 language code.
func (b Base) ISO3() string {
return b.langID.ISO3()
// IsPrivateUse reports whether this language code is reserved for private use.
func (b Base) IsPrivateUse() bool {
return b.langID.IsPrivateUse()
// Script is a 4-letter ISO 15924 code for representing scripts.
// It is idiomatically represented in title case.
type Script struct {
scriptID language.Script
// ParseScript parses a 4-letter ISO 15924 code.
// It returns a ValueError if s is a well-formed but unknown script identifier
// or another error if another error occurred.
func ParseScript(s string) (Script, error) {
sc, err := language.ParseScript(s)
return Script{sc}, err
// String returns the script code in title case.
// It returns "Zzzz" for an unspecified script.
func (s Script) String() string {
return s.scriptID.String()
// IsPrivateUse reports whether this script code is reserved for private use.
func (s Script) IsPrivateUse() bool {
return s.scriptID.IsPrivateUse()
// Region is an ISO 3166-1 or UN M.49 code for representing countries and regions.
type Region struct {
regionID language.Region
// EncodeM49 returns the Region for the given UN M.49 code.
// It returns an error if r is not a valid code.
func EncodeM49(r int) (Region, error) {
rid, err := language.EncodeM49(r)
return Region{rid}, err
// ParseRegion parses a 2- or 3-letter ISO 3166-1 or a UN M.49 code.
// It returns a ValueError if s is a well-formed but unknown region identifier
// or another error if another error occurred.
func ParseRegion(s string) (Region, error) {
r, err := language.ParseRegion(s)
return Region{r}, err
// String returns the BCP 47 representation for the region.
// It returns "ZZ" for an unspecified region.
func (r Region) String() string {
return r.regionID.String()
// ISO3 returns the 3-letter ISO code of r.
// Note that not all regions have a 3-letter ISO code.
// In such cases this method returns "ZZZ".
func (r Region) ISO3() string {
return r.regionID.String()
// M49 returns the UN M.49 encoding of r, or 0 if this encoding
// is not defined for r.
func (r Region) M49() int {
return r.regionID.M49()
// IsPrivateUse reports whether r has the ISO 3166 User-assigned status. This
// may include private-use tags that are assigned by CLDR and used in this
// implementation. So IsPrivateUse and IsCountry can be simultaneously true.
func (r Region) IsPrivateUse() bool {
return r.regionID.IsPrivateUse()
// IsCountry returns whether this region is a country or autonomous area. This
// includes non-standard definitions from CLDR.
func (r Region) IsCountry() bool {
return r.regionID.IsCountry()
// IsGroup returns whether this region defines a collection of regions. This
// includes non-standard definitions from CLDR.
func (r Region) IsGroup() bool {
return r.regionID.IsGroup()
// Contains returns whether Region c is contained by Region r. It returns true
// if c == r.
func (r Region) Contains(c Region) bool {
return r.regionID.Contains(c.regionID)
// TLD returns the country code top-level domain (ccTLD). UK is returned for GB.
// In all other cases it returns either the region itself or an error.
// This method may return an error for a region for which there exists a
// canonical form with a ccTLD. To get that ccTLD canonicalize r first. The
// region will already be canonicalized it was obtained from a Tag that was
// obtained using any of the default methods.
func (r Region) TLD() (Region, error) {
tld, err := r.regionID.TLD()
return Region{tld}, err
// Canonicalize returns the region or a possible replacement if the region is
// deprecated. It will not return a replacement for deprecated regions that
// are split into multiple regions.
func (r Region) Canonicalize() Region {
return Region{r.regionID.Canonicalize()}
// Variant represents a registered variant of a language as defined by BCP 47.
type Variant struct {
variant string
// ParseVariant parses and returns a Variant. An error is returned if s is not
// a valid variant.
func ParseVariant(s string) (Variant, error) {
v, err := language.ParseVariant(s)
return Variant{v.String()}, err
// String returns the string representation of the variant.
func (v Variant) String() string {
return v.variant