Source: match.go in package golang.org/x/text/internal/language


package language

import "errors"

type scriptRegionFlags uint8

const (
	isList = 1 << iota
	scriptInFrom
	regionInFrom
)

func (t *Tag) setUndefinedLang(id Language) {
	if t.LangID == 0 {
		t.LangID = id
	}
}

func (t *Tag) setUndefinedScript(id Script) {
	if t.ScriptID == 0 {
		t.ScriptID = id
	}
}

func (t *Tag) setUndefinedRegion(id Region) {
	if t.RegionID == 0 || t.RegionID.Contains(id) {
		t.RegionID = id
	}
}

ErrMissingLikelyTagsData indicates no information was available to compute likely values of missing tags.

var ErrMissingLikelyTagsData = errors.New("missing likely tags data")

addLikelySubtags sets subtags to their most likely value, given the locale. In most cases this means setting fields for unknown values, but in some cases it may alter a value. It returns an ErrMissingLikelyTagsData error if the given locale cannot be expanded.

func (t Tag) addLikelySubtags() (Tag, error) {
	id, err := addTags(t)
	if err != nil {
		return t, err
	} else if id.equalTags(t) {
		return t, nil
	}
	id.RemakeString()
	return id, nil
}

specializeRegion attempts to specialize a group region.

func specializeRegion(t *Tag) bool {
	if i := regionInclusion[t.RegionID]; i < nRegionGroups {
		x := likelyRegionGroup[i]
		if Language(x.lang) == t.LangID && Script(x.script) == t.ScriptID {
			t.RegionID = Region(x.region)
		}
		return true
	}
	return false
}

Maximize returns a new tag with missing tags filled in.

func (t Tag) Maximize() (Tag, error) {
	return addTags(t)
}

We leave private use identifiers alone.

	if t.IsPrivateUse() {
		return t, nil
	}
	if t.ScriptID != 0 && t.RegionID != 0 {

already fully specified

			specializeRegion(&t)
			return t, nil

Search matches for und-script-region. Note that for these cases region will never be a group so there is no need to check for this.

		list := likelyRegion[t.RegionID : t.RegionID+1]
		if x := list[0]; x.flags&isList != 0 {
			list = likelyRegionList[x.lang : x.lang+uint16(x.script)]
		}

Deviating from the spec. See match_test.go for details.

			if Script(x.script) == t.ScriptID {
				t.setUndefinedLang(Language(x.lang))
				return t, nil
			}
		}
	}

Search matches for lang-script and lang-region, where lang != und.

		if t.LangID < langNoIndexOffset {
			x := likelyLang[t.LangID]
			if x.flags&isList != 0 {
				list := likelyLangList[x.region : x.region+uint16(x.script)]
				if t.ScriptID != 0 {
					for _, x := range list {
						if Script(x.script) == t.ScriptID && x.flags&scriptInFrom != 0 {
							t.setUndefinedRegion(Region(x.region))
							return t, nil
						}
					}
				} else if t.RegionID != 0 {
					count := 0
					goodScript := true
					tt := t

We visit all entries for which the script was not defined, including the ones where the region was not defined. This allows for proper disambiguation within regions.

						if x.flags&scriptInFrom == 0 && t.RegionID.Contains(Region(x.region)) {
							tt.RegionID = Region(x.region)
							tt.setUndefinedScript(Script(x.script))
							goodScript = goodScript && tt.ScriptID == Script(x.script)
							count++
						}
					}
					if count == 1 {
						return tt, nil

Even if we fail to find a unique Region, we might have an unambiguous script.

					if goodScript {
						t.ScriptID = tt.ScriptID
					}
				}
			}
		}

Search matches for und-script.

		if t.ScriptID != 0 {
			x := likelyScript[t.ScriptID]
			if x.region != 0 {
				t.setUndefinedRegion(Region(x.region))
				t.setUndefinedLang(Language(x.lang))
				return t, nil
			}

Search matches for und-region. If und-script-region exists, it would have been found earlier.

		if t.RegionID != 0 {
			if i := regionInclusion[t.RegionID]; i < nRegionGroups {
				x := likelyRegionGroup[i]
				if x.region != 0 {
					t.setUndefinedLang(Language(x.lang))
					t.setUndefinedScript(Script(x.script))
					t.RegionID = Region(x.region)
				}
			} else {
				x := likelyRegion[t.RegionID]
				if x.flags&isList != 0 {
					x = likelyRegionList[x.lang]
				}
				if x.script != 0 && x.flags != scriptInFrom {
					t.setUndefinedLang(Language(x.lang))
					t.setUndefinedScript(Script(x.script))
					return t, nil
				}
			}
		}
	}

Search matches for lang.

	if t.LangID < langNoIndexOffset {
		x := likelyLang[t.LangID]
		if x.flags&isList != 0 {
			x = likelyLangList[x.region]
		}
		if x.region != 0 {
			t.setUndefinedScript(Script(x.script))
			t.setUndefinedRegion(Region(x.region))
		}
		specializeRegion(&t)
		if t.LangID == 0 {
			t.LangID = _en // default language
		}
		return t, nil
	}
	return t, ErrMissingLikelyTagsData
}

func (t *Tag) setTagsFrom(id Tag) {
	t.LangID = id.LangID
	t.ScriptID = id.ScriptID
	t.RegionID = id.RegionID
}

minimize removes the region or script subtags from t such that t.addLikelySubtags() == t.minimize().addLikelySubtags().

func (t Tag) minimize() (Tag, error) {
	t, err := minimizeTags(t)
	if err != nil {
		return t, err
	}
	t.RemakeString()
	return t, nil
}

minimizeTags mimics the behavior of the ICU 51 C implementation.

func minimizeTags(t Tag) (Tag, error) {
	if t.equalTags(Und) {
		return t, nil
	}
	max, err := addTags(t)
	if err != nil {
		return t, err
	}
	for _, id := range [...]Tag{
		{LangID: t.LangID},
		{LangID: t.LangID, RegionID: t.RegionID},
		{LangID: t.LangID, ScriptID: t.ScriptID},
	} {
		if x, err := addTags(id); err == nil && max.equalTags(x) {
			t.setTagsFrom(id)
			break
		}
	}
	return t, nil