Fix LocaleDisplay crash on odd-length generic BCP 47 extension subtags

Author: kipcole9

CHANGELOG.md

@@ -14,6 +14,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 * `Localize.Locale.Provider.locale_cache_dir/0` validates its configuration at app start (via `Localize.Supervisor`) and raises `Localize.LocaleCacheDirError` instead of silently reading from the wrong directory at runtime.
 
+* `Localize.Locale.LocaleDisplay.display_name/2` no longer raises `FunctionClauseError` on a BCP 47 generic extension carrying an odd number of subtags (e.g. `cr-s-7b`); the trailing singleton chunk now renders as a bare subtag.
+
 ### Enhancements
 
 * New `:otp_app` config key. Three supported forms for the locale cache directory: (1) `:otp_app` only → `Application.app_dir(<otp_app>, "priv/localize/locales")`; (2) `:otp_app` + relative `:locale_cache_dir` → `Application.app_dir(<otp_app>, <relative>)`; (3) absolute `:locale_cache_dir` → used verbatim, `:otp_app` ignored.

lib/localize/locale/locale_display/extension.ex

@@ -30,10 +30,21 @@ defmodule Localize.Locale.LocaleDisplay.Extension do
         Localize.Substitution.substitute(["x", value_names], key_type_pattern)
 
       {extension, key_value_pairs} when is_list(key_value_pairs) ->
+        # Generic BCP 47 extensions (singletons other than `u` and `t`)
+        # carry one or more 2–8 alphanumeric subtags. CLDR's locale
+        # display pattern pairs them as key/type, but an odd-length
+        # subtag list is well-formed BCP 47 — render the trailing
+        # singleton as a bare subtag rather than crashing. (Property
+        # regression: `Cr-S-7B` parses to extension `s` with value
+        # `["7b"]`, which chunked to `[["7b"]]` did not match the
+        # 2-element pattern.)
         value_names =
           key_value_pairs
           |> Enum.chunk_every(2)
-          |> Enum.map(fn [key, value] -> "#{key}-#{value}" end)
+          |> Enum.map(fn
+            [key, value] -> "#{key}-#{value}"
+            [value] -> "#{value}"
+          end)
           |> join_field_values(display_names)
 
         Localize.Substitution.substitute([extension, value_names], key_type_pattern)

test/localize/locale/locale_display_test.exs

@@ -177,6 +177,24 @@ defmodule Localize.Locale.LocaleDisplayTest do
       result = Localize.Locale.LocaleDisplay.display_name("xyz-invalid-totally-bad")
       assert match?({:error, _}, result)
     end
+
+    # Regression: a generic BCP 47 extension with an odd number of
+    # subtags (e.g. `cr-s-7b` — extension singleton `s` carrying a
+    # single subtag `7b`) crashed in
+    # `Localize.Locale.LocaleDisplay.Extension.display_name/3` because
+    # `Enum.chunk_every(2)` produced a singleton chunk that did not
+    # match the `[key, value]` pattern. Caught by the
+    # `LocaleDisplay.display_name/2 adversarial` property — atom input
+    # `:Cr_S_7B` normalised to `cr-s-7b`.
+    test "odd-length generic extension subtag list renders without crashing" do
+      assert {:ok, name} = Localize.Locale.LocaleDisplay.display_name("cr-s-7b")
+      assert String.contains?(name, "Cree")
+      assert String.contains?(name, "7b")
+    end
+
+    test "atom form of the same input does not raise" do
+      assert {:ok, _name} = Localize.Locale.LocaleDisplay.display_name(:Cr_S_7B)
+    end
   end
 
   # Regression: `find_exemplar_city/2` (in `LocaleDisplay.U`) and