Changelog

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All notable changes to this project are documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

v0.3.0 - 2026-08-17

A feature release. Everything is additive; no existing behaviour changed, and the bundled registry is unchanged from v0.2.1.

Added

  • LangTags.Match implements RFC 4647 matching of language tags against language ranges, such as the ranges a client sends in an Accept-Language header. lookup/2 returns the single best tag, shortening a range one subtag at a time until something matches, and dropping a singleton along with the subtag that introduced it, so "zh-Hant-CN-x-private1-private2" falls back to "zh-Hant-CN" without ever trying "zh-Hant-CN-x". filter/2 implements basic filtering and returns every tag a range covers, requiring the prefix to be followed by -, so "de-DE" covers "de-DE-1996" but not "de-Deva". Both compare case-insensitively and return tags in the casing they were given. Neither consults the registry, so the module adds nothing to compile time. lookup/2 returns nil for the RFC's notion of a default value, which the RFC leaves to each application to define.
  • LangTags.Tag.extensions/1 returns a tag's extension sequences as a map keyed by singleton, and LangTags.Tag.private_use/1 returns the subtags following x. subtags/1 stops at the first singleton, so these sequences were parsed and then discarded with no way to reach them. The map is lossless because RFC 5646 forbids a singleton from appearing twice in a tag. Grandfathered tags are registered whole, so both return empty for them, as subtags/1 already does.
  • LangTags.all/1 returns every registered subtag of a given type as {code, type} pairs, for listing the regions or scripts behind a form or a picker. Previously every lookup needed a code you already had. It returns pairs rather than records, so listing 9203 subtags does not build 9203 maps; pass a code to type/2 for the full record. Deprecated subtags are included, since they are still registered. Grandfathered and redundant records are tags rather than subtags and are excluded, matching type/2.

v0.2.1 - 2026-08-11

A performance release. No behaviour changes.

Changed

  • The registry now compiles into lookup tables rather than one function clause per record. Generating 9203 subtag/2 clauses and 8919 types/1 clauses, each carrying its own map literal, accounted for about 16.6 of the module's 16.7 seconds. Compiling the project now takes about 1.5 seconds instead of about 16.6. Lookups remain constant time on a term embedded in the compiled module, so nothing is parsed, copied or supervised at runtime.

Fixed

  • LangTags.Tag.new/1 and LangTags.SubTag.find/2 used exceptions for control flow on their most common paths. new/1 raised and rescued for every tag that is neither grandfathered nor redundant, which is almost every tag, and find/2 raised whenever a code was not of the type being probed, which happens several times per tag. Raising cost about 44us against roughly 1us for the lookup itself. Both now use new non-raising lookups on the internal registry module, which return a tagged tuple rather than raising when a record is absent. Tag.valid?/1 went from about 174us to about 2.5us. The public behaviour of both functions is unchanged.

v0.2.0 - 2026-08-11

Published to Hex on 2026-08-11.

The first release since v0.1.0 on 2016-12-19. It refreshes a decade of registry data, repairs tag validation, and brings the project back onto a supported toolchain.

Registry data

The bundled IANA language subtag registry moved from 2016-10-12 to 2026-08-08, growing from 9001 to 9296 records.

This is the change most likely to affect you. Anyone on v0.1.0 has been resolving language tags against data from 2016, so subtags added since then were reported as unregistered and subtags deprecated since then were reported as current.

Two consequences worth calling out, both upstream corrections rather than changes in this library:

  • Descriptions have changed. For example Klingon's second description lost its hyphen, "tlhIngan-Hol" becoming "tlhIngan Hol".
  • Tags that were valid in 2016 may no longer be. For example hy-Latn-IT-arevela, an example tag from RFC 5646 itself, is now invalid because the arevela variant was deprecated in 2018 in favour of hy.

Added

  • mix lang_tags.update fetches the current registry from IANA and writes it to priv/. It validates the download before replacing the bundled copy, so an error page or a truncated body cannot clobber it. Pass --check to report whether an update is available without writing; it exits non-zero when one is, so it can drive a scheduled job. It uses OTP's own HTTP client and adds no dependency.
  • LangTags.search/2 searches tag and subtag descriptions. It accepts a string, matched case-insensitively against any part of a description, or a Regex. Exact description matches are returned first and the rest follow in registry order. Grandfathered and redundant tags are excluded unless the all argument is true. The function had been present but commented out since 2016.
  • LangTags.Tag.errors/1 is now documented public API with a @spec and a @type. It reports every reason a tag is invalid rather than stopping at the first.
  • Continuous integration on GitHub Actions, covering Elixir 1.15 through 1.20 and OTP 26 through 29, with formatting, unused-dependency and Credo checks.
  • A .formatter.exs, and a .git-blame-ignore-revs so the commit that first applied it does not obscure git blame.

Changed

  • Requires Elixir ~> 1.15.
  • LangTags.Tag.errors/1 returns a list of maps shaped %{code: atom, subtag: String.t(), message: String.t()} instead of a list of strings such as "ERR_DEPRECATED". Callers learn which subtag failed rather than only that something did. See the documentation for the full list of codes.
  • The application spec no longer lists :logger. The library uses it nowhere and starts no processes, so consumers building for production get an empty spec.
  • The package now declares its license using the SPDX identifier Apache-2.0.

Fixed

  • LangTags.Tag.valid?/1 returned the wrong answer and crashed on invalid input. The condition that added the "no language" error fired when the first subtag was a language, so valid?("en") returned false, and a tag whose subtags could not be resolved raised FunctionClauseError instead of returning false. Both were reachable through LangTags.check/1. Validation is now implemented against RFC 5646 section 2.2.9 and additionally checks for duplicate subtag types, canonical subtag order, and deprecated subtags, none of which were checked before.
  • Formatting a script or four-letter subtag raised UndefinedFunctionError on any recent Elixir. The library called String.Casing.titlecase_once/1, a private Elixir internal that has since been removed. It now uses String.capitalize/1, which also handles mixed-case input correctly: "az-LATN" now formats as "az-Latn" rather than "az-LATN".

Removed

  • The config/ directory. It configured nothing, and configuration in a dependency is not loaded by the parent project anyway.
  • .travis.yml, replaced by GitHub Actions.
  • The earmark dependency, which is retired on Hex. ExDoc bundles its own markdown parser.

v0.1.0 - 2016-12-19

Initial release.