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Diffstat (limited to 'vendor/golang.org/x/text/language/match.go')
| -rw-r--r-- | vendor/golang.org/x/text/language/match.go | 735 |
1 files changed, 735 insertions, 0 deletions
diff --git a/vendor/golang.org/x/text/language/match.go b/vendor/golang.org/x/text/language/match.go new file mode 100644 index 00000000..f7349213 --- /dev/null +++ b/vendor/golang.org/x/text/language/match.go @@ -0,0 +1,735 @@ +// 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. + +package language + +import ( + "errors" + "strings" + + "golang.org/x/text/internal/language" +) + +// A MatchOption configures a Matcher. +type MatchOption func(*matcher) + +// PreferSameScript will, in the absence of a match, result in the first +// preferred tag with the same script as a supported tag to match this supported +// tag. The default is currently true, but this may change in the future. +func PreferSameScript(preferSame bool) MatchOption { + return func(m *matcher) { m.preferSameScript = preferSame } +} + +// TODO(v1.0.0): consider making Matcher a concrete type, instead of interface. +// There doesn't seem to be too much need for multiple types. +// Making it a concrete type allows MatchStrings to be a method, which will +// improve its discoverability. + +// MatchStrings parses and matches the given strings until one of them matches +// the language in the Matcher. A string may be an Accept-Language header as +// handled by ParseAcceptLanguage. The default language is returned if no +// other language matched. +func MatchStrings(m Matcher, lang ...string) (tag Tag, index int) { + for _, accept := range lang { + desired, _, err := ParseAcceptLanguage(accept) + if err != nil { + continue + } + if tag, index, conf := m.Match(desired...); conf != No { + return tag, index + } + } + tag, index, _ = m.Match() + return +} + +// Matcher is the interface that wraps the Match method. +// +// Match returns the best match for any of the given tags, along with +// a unique index associated with the returned tag and a confidence +// score. +type Matcher interface { + Match(t ...Tag) (tag Tag, index int, c Confidence) +} + +// Comprehends reports the confidence score for a speaker of a given language +// to being able to comprehend the written form of an alternative language. +func Comprehends(speaker, alternative Tag) Confidence { + _, _, c := NewMatcher([]Tag{alternative}).Match(speaker) + return c +} + +// NewMatcher returns a Matcher that matches an ordered list of preferred tags +// against a list of supported tags based on written intelligibility, closeness +// of dialect, equivalence of subtags and various other rules. It is initialized +// with the list of supported tags. The first element is used as the default +// value in case no match is found. +// +// Its Match method matches the first of the given Tags to reach a certain +// confidence threshold. The tags passed to Match should therefore be specified +// in order of preference. Extensions are ignored for matching. +// +// The index returned by the Match method corresponds to the index of the +// matched tag in t, but is augmented with the Unicode extension ('u')of the +// corresponding preferred tag. This allows user locale options to be passed +// transparently. +func NewMatcher(t []Tag, options ...MatchOption) Matcher { + return newMatcher(t, options) +} + +func (m *matcher) Match(want ...Tag) (t Tag, index int, c Confidence) { + var tt language.Tag + match, w, c := m.getBest(want...) + if match != nil { + tt, index = match.tag, match.index + } else { + // TODO: this should be an option + tt = m.default_.tag + if m.preferSameScript { + outer: + for _, w := range want { + script, _ := w.Script() + if script.scriptID == 0 { + // Don't do anything if there is no script, such as with + // private subtags. + continue + } + for i, h := range m.supported { + if script.scriptID == h.maxScript { + tt, index = h.tag, i + break outer + } + } + } + } + // TODO: select first language tag based on script. + } + if w.RegionID != tt.RegionID && w.RegionID != 0 { + if w.RegionID != 0 && tt.RegionID != 0 && tt.RegionID.Contains(w.RegionID) { + tt.RegionID = w.RegionID + tt.RemakeString() + } else if r := w.RegionID.String(); len(r) == 2 { + // TODO: also filter macro and deprecated. + tt, _ = tt.SetTypeForKey("rg", strings.ToLower(r)+"zzzz") + } + } + // Copy options from the user-provided tag into the result tag. This is hard + // to do after the fact, so we do it here. + // TODO: add in alternative variants to -u-va-. + // TODO: add preferred region to -u-rg-. + if e := w.Extensions(); len(e) > 0 { + b := language.Builder{} + b.SetTag(tt) + for _, e := range e { + b.AddExt(e) + } + tt = b.Make() + } + return makeTag(tt), index, c +} + +// ErrMissingLikelyTagsData indicates no information was available +// to compute likely values of missing tags. +var ErrMissingLikelyTagsData = errors.New("missing likely tags data") + +// func (t *Tag) setTagsFrom(id Tag) { +// t.LangID = id.LangID +// t.ScriptID = id.ScriptID +// t.RegionID = id.RegionID +// } + +// Tag Matching +// CLDR defines an algorithm for finding the best match between two sets of language +// tags. The basic algorithm defines how to score a possible match and then find +// the match with the best score +// (see https://www.unicode.org/reports/tr35/#LanguageMatching). +// Using scoring has several disadvantages. The scoring obfuscates the importance of +// the various factors considered, making the algorithm harder to understand. Using +// scoring also requires the full score to be computed for each pair of tags. +// +// We will use a different algorithm which aims to have the following properties: +// - clarity on the precedence of the various selection factors, and +// - improved performance by allowing early termination of a comparison. +// +// Matching algorithm (overview) +// Input: +// - supported: a set of supported tags +// - default: the default tag to return in case there is no match +// - desired: list of desired tags, ordered by preference, starting with +// the most-preferred. +// +// Algorithm: +// 1) Set the best match to the lowest confidence level +// 2) For each tag in "desired": +// a) For each tag in "supported": +// 1) compute the match between the two tags. +// 2) if the match is better than the previous best match, replace it +// with the new match. (see next section) +// b) if the current best match is Exact and pin is true the result will be +// frozen to the language found thusfar, although better matches may +// still be found for the same language. +// 3) If the best match so far is below a certain threshold, return "default". +// +// Ranking: +// We use two phases to determine whether one pair of tags are a better match +// than another pair of tags. First, we determine a rough confidence level. If the +// levels are different, the one with the highest confidence wins. +// Second, if the rough confidence levels are identical, we use a set of tie-breaker +// rules. +// +// The confidence level of matching a pair of tags is determined by finding the +// lowest confidence level of any matches of the corresponding subtags (the +// result is deemed as good as its weakest link). +// We define the following levels: +// Exact - An exact match of a subtag, before adding likely subtags. +// MaxExact - An exact match of a subtag, after adding likely subtags. +// [See Note 2]. +// High - High level of mutual intelligibility between different subtag +// variants. +// Low - Low level of mutual intelligibility between different subtag +// variants. +// No - No mutual intelligibility. +// +// The following levels can occur for each type of subtag: +// Base: Exact, MaxExact, High, Low, No +// Script: Exact, MaxExact [see Note 3], Low, No +// Region: Exact, MaxExact, High +// Variant: Exact, High +// Private: Exact, No +// +// Any result with a confidence level of Low or higher is deemed a possible match. +// Once a desired tag matches any of the supported tags with a level of MaxExact +// or higher, the next desired tag is not considered (see Step 2.b). +// Note that CLDR provides languageMatching data that defines close equivalence +// classes for base languages, scripts and regions. +// +// Tie-breaking +// If we get the same confidence level for two matches, we apply a sequence of +// tie-breaking rules. The first that succeeds defines the result. The rules are +// applied in the following order. +// 1) Original language was defined and was identical. +// 2) Original region was defined and was identical. +// 3) Distance between two maximized regions was the smallest. +// 4) Original script was defined and was identical. +// 5) Distance from want tag to have tag using the parent relation [see Note 5.] +// If there is still no winner after these rules are applied, the first match +// found wins. +// +// Notes: +// [2] In practice, as matching of Exact is done in a separate phase from +// matching the other levels, we reuse the Exact level to mean MaxExact in +// the second phase. As a consequence, we only need the levels defined by +// the Confidence type. The MaxExact confidence level is mapped to High in +// the public API. +// [3] We do not differentiate between maximized script values that were derived +// from suppressScript versus most likely tag data. We determined that in +// ranking the two, one ranks just after the other. Moreover, the two cannot +// occur concurrently. As a consequence, they are identical for practical +// purposes. +// [4] In case of deprecated, macro-equivalents and legacy mappings, we assign +// the MaxExact level to allow iw vs he to still be a closer match than +// en-AU vs en-US, for example. +// [5] In CLDR a locale inherits fields that are unspecified for this locale +// from its parent. Therefore, if a locale is a parent of another locale, +// it is a strong measure for closeness, especially when no other tie +// breaker rule applies. One could also argue it is inconsistent, for +// example, when pt-AO matches pt (which CLDR equates with pt-BR), even +// though its parent is pt-PT according to the inheritance rules. +// +// Implementation Details: +// There are several performance considerations worth pointing out. Most notably, +// we preprocess as much as possible (within reason) at the time of creation of a +// matcher. This includes: +// - creating a per-language map, which includes data for the raw base language +// and its canonicalized variant (if applicable), +// - expanding entries for the equivalence classes defined in CLDR's +// languageMatch data. +// The per-language map ensures that typically only a very small number of tags +// need to be considered. The pre-expansion of canonicalized subtags and +// equivalence classes reduces the amount of map lookups that need to be done at +// runtime. + +// matcher keeps a set of supported language tags, indexed by language. +type matcher struct { + default_ *haveTag + supported []*haveTag + index map[language.Language]*matchHeader + passSettings bool + preferSameScript bool +} + +// matchHeader has the lists of tags for exact matches and matches based on +// maximized and canonicalized tags for a given language. +type matchHeader struct { + haveTags []*haveTag + original bool +} + +// haveTag holds a supported Tag and its maximized script and region. The maximized +// or canonicalized language is not stored as it is not needed during matching. +type haveTag struct { + tag language.Tag + + // index of this tag in the original list of supported tags. + index int + + // conf is the maximum confidence that can result from matching this haveTag. + // When conf < Exact this means it was inserted after applying a CLDR equivalence rule. + conf Confidence + + // Maximized region and script. + maxRegion language.Region + maxScript language.Script + + // altScript may be checked as an alternative match to maxScript. If altScript + // matches, the confidence level for this match is Low. Theoretically there + // could be multiple alternative scripts. This does not occur in practice. + altScript language.Script + + // nextMax is the index of the next haveTag with the same maximized tags. + nextMax uint16 +} + +func makeHaveTag(tag language.Tag, index int) (haveTag, language.Language) { + max := tag + if tag.LangID != 0 || tag.RegionID != 0 || tag.ScriptID != 0 { + max, _ = canonicalize(All, max) + max, _ = max.Maximize() + max.RemakeString() + } + return haveTag{tag, index, Exact, max.RegionID, max.ScriptID, altScript(max.LangID, max.ScriptID), 0}, max.LangID +} + +// altScript returns an alternative script that may match the given script with +// a low confidence. At the moment, the langMatch data allows for at most one +// script to map to another and we rely on this to keep the code simple. +func altScript(l language.Language, s language.Script) language.Script { + for _, alt := range matchScript { + // TODO: also match cases where language is not the same. + if (language.Language(alt.wantLang) == l || language.Language(alt.haveLang) == l) && + language.Script(alt.haveScript) == s { + return language.Script(alt.wantScript) + } + } + return 0 +} + +// addIfNew adds a haveTag to the list of tags only if it is a unique tag. +// Tags that have the same maximized values are linked by index. +func (h *matchHeader) addIfNew(n haveTag, exact bool) { + h.original = h.original || exact + // Don't add new exact matches. + for _, v := range h.haveTags { + if equalsRest(v.tag, n.tag) { + return + } + } + // Allow duplicate maximized tags, but create a linked list to allow quickly + // comparing the equivalents and bail out. + for i, v := range h.haveTags { + if v.maxScript == n.maxScript && + v.maxRegion == n.maxRegion && + v.tag.VariantOrPrivateUseTags() == n.tag.VariantOrPrivateUseTags() { + for h.haveTags[i].nextMax != 0 { + i = int(h.haveTags[i].nextMax) + } + h.haveTags[i].nextMax = uint16(len(h.haveTags)) + break + } + } + h.haveTags = append(h.haveTags, &n) +} + +// header returns the matchHeader for the given language. It creates one if +// it doesn't already exist. +func (m *matcher) header(l language.Language) *matchHeader { + if h := m.index[l]; h != nil { + return h + } + h := &matchHeader{} + m.index[l] = h + return h +} + +func toConf(d uint8) Confidence { + if d <= 10 { + return High + } + if d < 30 { + return Low + } + return No +} + +// newMatcher builds an index for the given supported tags and returns it as +// a matcher. It also expands the index by considering various equivalence classes +// for a given tag. +func newMatcher(supported []Tag, options []MatchOption) *matcher { + m := &matcher{ + index: make(map[language.Language]*matchHeader), + preferSameScript: true, + } + for _, o := range options { + o(m) + } + if len(supported) == 0 { + m.default_ = &haveTag{} + return m + } + // Add supported languages to the index. Add exact matches first to give + // them precedence. + for i, tag := range supported { + tt := tag.tag() + pair, _ := makeHaveTag(tt, i) + m.header(tt.LangID).addIfNew(pair, true) + m.supported = append(m.supported, &pair) + } + m.default_ = m.header(supported[0].lang()).haveTags[0] + // Keep these in two different loops to support the case that two equivalent + // languages are distinguished, such as iw and he. + for i, tag := range supported { + tt := tag.tag() + pair, max := makeHaveTag(tt, i) + if max != tt.LangID { + m.header(max).addIfNew(pair, true) + } + } + + // update is used to add indexes in the map for equivalent languages. + // update will only add entries to original indexes, thus not computing any + // transitive relations. + update := func(want, have uint16, conf Confidence) { + if hh := m.index[language.Language(have)]; hh != nil { + if !hh.original { + return + } + hw := m.header(language.Language(want)) + for _, ht := range hh.haveTags { + v := *ht + if conf < v.conf { + v.conf = conf + } + v.nextMax = 0 // this value needs to be recomputed + if v.altScript != 0 { + v.altScript = altScript(language.Language(want), v.maxScript) + } + hw.addIfNew(v, conf == Exact && hh.original) + } + } + } + + // Add entries for languages with mutual intelligibility as defined by CLDR's + // languageMatch data. + for _, ml := range matchLang { + update(ml.want, ml.have, toConf(ml.distance)) + if !ml.oneway { + update(ml.have, ml.want, toConf(ml.distance)) + } + } + + // Add entries for possible canonicalizations. This is an optimization to + // ensure that only one map lookup needs to be done at runtime per desired tag. + // First we match deprecated equivalents. If they are perfect equivalents + // (their canonicalization simply substitutes a different language code, but + // nothing else), the match confidence is Exact, otherwise it is High. + for i, lm := range language.AliasMap { + // If deprecated codes match and there is no fiddling with the script or + // or region, we consider it an exact match. + conf := Exact + if language.AliasTypes[i] != language.Macro { + if !isExactEquivalent(language.Language(lm.From)) { + conf = High + } + update(lm.To, lm.From, conf) + } + update(lm.From, lm.To, conf) + } + return m +} + +// getBest gets the best matching tag in m for any of the given tags, taking into +// account the order of preference of the given tags. +func (m *matcher) getBest(want ...Tag) (got *haveTag, orig language.Tag, c Confidence) { + best := bestMatch{} + for i, ww := range want { + w := ww.tag() + var max language.Tag + // Check for exact match first. + h := m.index[w.LangID] + if w.LangID != 0 { + if h == nil { + continue + } + // Base language is defined. + max, _ = canonicalize(Legacy|Deprecated|Macro, w) + // A region that is added through canonicalization is stronger than + // a maximized region: set it in the original (e.g. mo -> ro-MD). + if w.RegionID != max.RegionID { + w.RegionID = max.RegionID + } + // TODO: should we do the same for scripts? + // See test case: en, sr, nl ; sh ; sr + max, _ = max.Maximize() + } else { + // Base language is not defined. + if h != nil { + for i := range h.haveTags { + have := h.haveTags[i] + if equalsRest(have.tag, w) { + return have, w, Exact + } + } + } + if w.ScriptID == 0 && w.RegionID == 0 { + // We skip all tags matching und for approximate matching, including + // private tags. + continue + } + max, _ = w.Maximize() + if h = m.index[max.LangID]; h == nil { + continue + } + } + pin := true + for _, t := range want[i+1:] { + if w.LangID == t.lang() { + pin = false + break + } + } + // Check for match based on maximized tag. + for i := range h.haveTags { + have := h.haveTags[i] + best.update(have, w, max.ScriptID, max.RegionID, pin) + if best.conf == Exact { + for have.nextMax != 0 { + have = h.haveTags[have.nextMax] + best.update(have, w, max.ScriptID, max.RegionID, pin) + } + return best.have, best.want, best.conf + } + } + } + if best.conf <= No { + if len(want) != 0 { + return nil, want[0].tag(), No + } + return nil, language.Tag{}, No + } + return best.have, best.want, best.conf +} + +// bestMatch accumulates the best match so far. +type bestMatch struct { + have *haveTag + want language.Tag + conf Confidence + pinnedRegion language.Region + pinLanguage bool + sameRegionGroup bool + // Cached results from applying tie-breaking rules. + origLang bool + origReg bool + paradigmReg bool + regGroupDist uint8 + origScript bool +} + +// update updates the existing best match if the new pair is considered to be a +// better match. To determine if the given pair is a better match, it first +// computes the rough confidence level. If this surpasses the current match, it +// will replace it and update the tie-breaker rule cache. If there is a tie, it +// proceeds with applying a series of tie-breaker rules. If there is no +// conclusive winner after applying the tie-breaker rules, it leaves the current +// match as the preferred match. +// +// If pin is true and have and tag are a strong match, it will henceforth only +// consider matches for this language. This corresponds to the nothing that most +// users have a strong preference for the first defined language. A user can +// still prefer a second language over a dialect of the preferred language by +// explicitly specifying dialects, e.g. "en, nl, en-GB". In this case pin should +// be false. +func (m *bestMatch) update(have *haveTag, tag language.Tag, maxScript language.Script, maxRegion language.Region, pin bool) { + // Bail if the maximum attainable confidence is below that of the current best match. + c := have.conf + if c < m.conf { + return + } + // Don't change the language once we already have found an exact match. + if m.pinLanguage && tag.LangID != m.want.LangID { + return + } + // Pin the region group if we are comparing tags for the same language. + if tag.LangID == m.want.LangID && m.sameRegionGroup { + _, sameGroup := regionGroupDist(m.pinnedRegion, have.maxRegion, have.maxScript, m.want.LangID) + if !sameGroup { + return + } + } + if c == Exact && have.maxScript == maxScript { + // If there is another language and then another entry of this language, + // don't pin anything, otherwise pin the language. + m.pinLanguage = pin + } + if equalsRest(have.tag, tag) { + } else if have.maxScript != maxScript { + // There is usually very little comprehension between different scripts. + // In a few cases there may still be Low comprehension. This possibility + // is pre-computed and stored in have.altScript. + if Low < m.conf || have.altScript != maxScript { + return + } + c = Low + } else if have.maxRegion != maxRegion { + if High < c { + // There is usually a small difference between languages across regions. + c = High + } + } + + // We store the results of the computations of the tie-breaker rules along + // with the best match. There is no need to do the checks once we determine + // we have a winner, but we do still need to do the tie-breaker computations. + // We use "beaten" to keep track if we still need to do the checks. + beaten := false // true if the new pair defeats the current one. + if c != m.conf { + if c < m.conf { + return + } + beaten = true + } + + // Tie-breaker rules: + // We prefer if the pre-maximized language was specified and identical. + origLang := have.tag.LangID == tag.LangID && tag.LangID != 0 + if !beaten && m.origLang != origLang { + if m.origLang { + return + } + beaten = true + } + + // We prefer if the pre-maximized region was specified and identical. + origReg := have.tag.RegionID == tag.RegionID && tag.RegionID != 0 + if !beaten && m.origReg != origReg { + if m.origReg { + return + } + beaten = true + } + + regGroupDist, sameGroup := regionGroupDist(have.maxRegion, maxRegion, maxScript, tag.LangID) + if !beaten && m.regGroupDist != regGroupDist { + if regGroupDist > m.regGroupDist { + return + } + beaten = true + } + + paradigmReg := isParadigmLocale(tag.LangID, have.maxRegion) + if !beaten && m.paradigmReg != paradigmReg { + if !paradigmReg { + return + } + beaten = true + } + + // Next we prefer if the pre-maximized script was specified and identical. + origScript := have.tag.ScriptID == tag.ScriptID && tag.ScriptID != 0 + if !beaten && m.origScript != origScript { + if m.origScript { + return + } + beaten = true + } + + // Update m to the newly found best match. + if beaten { + m.have = have + m.want = tag + m.conf = c + m.pinnedRegion = maxRegion + m.sameRegionGroup = sameGroup + m.origLang = origLang + m.origReg = origReg + m.paradigmReg = paradigmReg + m.origScript = origScript + m.regGroupDist = regGroupDist + } +} + +func isParadigmLocale(lang language.Language, r language.Region) bool { + for _, e := range paradigmLocales { + if language.Language(e[0]) == lang && (r == language.Region(e[1]) || r == language.Region(e[2])) { + return true + } + } + return false +} + +// regionGroupDist computes the distance between two regions based on their +// CLDR grouping. +func regionGroupDist(a, b language.Region, script language.Script, lang language.Language) (dist uint8, same bool) { + const defaultDistance = 4 + + aGroup := uint(regionToGroups[a]) << 1 + bGroup := uint(regionToGroups[b]) << 1 + for _, ri := range matchRegion { + if language.Language(ri.lang) == lang && (ri.script == 0 || language.Script(ri.script) == script) { + group := uint(1 << (ri.group &^ 0x80)) + if 0x80&ri.group == 0 { + if aGroup&bGroup&group != 0 { // Both regions are in the group. + return ri.distance, ri.distance == defaultDistance + } + } else { + if (aGroup|bGroup)&group == 0 { // Both regions are not in the group. + return ri.distance, ri.distance == defaultDistance + } + } + } + } + return defaultDistance, true +} + +// equalsRest compares everything except the language. +func equalsRest(a, b language.Tag) bool { + // TODO: don't include extensions in this comparison. To do this efficiently, + // though, we should handle private tags separately. + return a.ScriptID == b.ScriptID && a.RegionID == b.RegionID && a.VariantOrPrivateUseTags() == b.VariantOrPrivateUseTags() +} + +// isExactEquivalent returns true if canonicalizing the language will not alter +// the script or region of a tag. +func isExactEquivalent(l language.Language) bool { + for _, o := range notEquivalent { + if o == l { + return false + } + } + return true +} + +var notEquivalent []language.Language + +func init() { + // Create a list of all languages for which canonicalization may alter the + // script or region. + for _, lm := range language.AliasMap { + tag := language.Tag{LangID: language.Language(lm.From)} + if tag, _ = canonicalize(All, tag); tag.ScriptID != 0 || tag.RegionID != 0 { + notEquivalent = append(notEquivalent, language.Language(lm.From)) + } + } + // Maximize undefined regions of paradigm locales. + for i, v := range paradigmLocales { + t := language.Tag{LangID: language.Language(v[0])} + max, _ := t.Maximize() + if v[1] == 0 { + paradigmLocales[i][1] = uint16(max.RegionID) + } + if v[2] == 0 { + paradigmLocales[i][2] = uint16(max.RegionID) + } + } +} |