1 files changed, 86 insertions, 0 deletions
diff --git a/lib/gitlab/i18n/pluralization.rb b/lib/gitlab/i18n/pluralization.rb
new file mode 100644
index 00000000000..5d4a05f1fd1
--- /dev/null
+++ b/lib/gitlab/i18n/pluralization.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module I18n
+    # Pluralization formulas per locale used by FastGettext via:
+    # `FastGettext.pluralisation_rule.call(count)`.
+    module Pluralization
+      # rubocop:disable all
+      MAP = {
+        "bg" => ->(n) { (n != 1) },
+        "cs_CZ" => ->(n) { (n==1) ? 0 : (n>=2 && n<=4) ? 1 : 3 },
+        "da_DK" => ->(n) { (n != 1) },
+        "de" => ->(n) { (n != 1) },
+        "en" => ->(n) { (n != 1) },
+        "eo" => ->(n) { (n != 1) },
+        "es" => ->(n) { (n != 1) },
+        "fil_PH" => ->(n) { (n > 1) },
+        "fr" => ->(n) { (n > 1) },
+        "gl_ES" => ->(n) { (n != 1) },
+        "id_ID" => ->(n) { 0 },
+        "it" => ->(n) { (n != 1) },
+        "ja" => ->(n) { 0 },
+        "ko" => ->(n) { 0 },
+        "nb_NO" => ->(n) { (n != 1) },
+        "nl_NL" => ->(n) { (n != 1) },
+        "pl_PL" => ->(n) { (n==1 ? 0 : (n%10>=2 && n%10<=4) && (n%100<12 || n%100>14) ? 1 : n!=1 && (n%10>=0 && n%10<=1) || (n%10>=5 && n%10<=9) || (n%100>=12 && n%100<=14) ? 2 : 3) },
+        "pt_BR" => ->(n) { (n != 1) },
+        "ro_RO" => ->(n) { (n==1 ? 0 : (n==0 || (n%100>0 && n%100<20)) ? 1 : 2) },
+        "ru" => ->(n) { ((n%10==1 && n%100!=11) ? 0 : ((n%10 >= 2 && n%10 <=4 && (n%100 < 12 || n%100 > 14)) ? 1 : ((n%10 == 0 || (n%10 >= 5 && n%10 <=9)) || (n%100 >= 11 && n%100 <= 14)) ? 2 : 3)) },
+        "si_LK" => ->(n) { (n != 1) },
+        "tr_TR" => ->(n) { (n != 1) },
+        "uk" => ->(n) { ((n%10==1 && n%100!=11) ? 0 : ((n%10 >= 2 && n%10 <=4 && (n%100 < 12 || n%100 > 14)) ? 1 : ((n%10 == 0 || (n%10 >= 5 && n%10 <=9)) || (n%100 >= 11 && n%100 <= 14)) ? 2 : 3)) },
+        "zh_CN" => ->(n) { 0 },
+        "zh_HK" => ->(n) { 0 },
+        "zh_TW" => ->(n) { 0 }
+      }.freeze
+      # rubocop:enable
+
+      NOT_FOUND_ERROR = lambda do |locale|
+        po = File.expand_path("../../../locale/#{locale}/gitlab.po", __dir__)
+
+        forms = File.read(po)[/Plural-Forms:.*; plural=(.*?);\\n/, 1] if File.exist?(po)
+        suggestion = <<~TEXT if forms
+          Add the following line to #{__FILE__}:
+
+            MAP = {
+              ...
+              "#{locale}" => ->(n) { #{forms} },
+              ...
+            }.freeze
+
+          This rule was extracted from #{po}.
+        TEXT
+
+        raise ArgumentError, <<~MESSAGE
+          Missing pluralization rule for locale #{locale.inspect}.
+
+          #{suggestion}
+        MESSAGE
+      end
+
+      def self.call(count)
+        locale = FastGettext.locale
+
+        MAP.fetch(locale, &NOT_FOUND_ERROR).call(count)
+      end
+
+      def self.install_on(klass)
+        klass.extend(FastGettextClassMethods)
+      end
+
+      module FastGettextClassMethods
+        # FastGettext allows to set the rule via
+        # `FastGettext.pluralisation_rule=` which is on thread-level.
+        #
+        # Because we are patching FastGettext at boot time per thread values
+        # won't work so we have to override the method implementation.
+        #
+        # `FastGettext.pluralisation_rule=` has now no effect.
+        def pluralisation_rule
+          Gitlab::I18n::Pluralization
+        end
+      end
+    end
+  end
+end