Remove redundant work from extraction, backend compilation and runtime interpolation

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+  * Call `c:Gettext.Plural.init/1` once per PO file at compile time instead of twice.
   * Add experimental `mix gettext.generate` task: messages are persisted as module attributes during normal compilation (for backends with `automatic_extraction: true` in the application environment, for example `config :gettext, MyApp.Gettext, automatic_extraction: true` in `config/dev.exs`) and read back from the compiled BEAM files, so extraction no longer needs to force-recompile the project.
 
 ## v1.1.0

lib/gettext/compiler.ex

@@ -498,8 +498,9 @@ defmodule Gettext.Compiler do
 
     plural_forms_fun = :"#{locale}_#{domain}_plural"
 
-    plural_forms = compile_plural_forms(locale, messages_struct, plural_mod, plural_forms_fun)
-    nplurals = nplurals(locale, messages_struct, plural_mod)
+    plural_info = Plural.plural_info(locale, messages_struct, plural_mod)
+    plural_forms = compile_plural_forms(plural_info, plural_mod, plural_forms_fun)
+    nplurals = nplurals(plural_info, plural_mod)
 
     singular_fun = :"#{locale}_#{domain}_lgettext"
     plural_fun = :"#{locale}_#{domain}_lngettext"
@@ -552,17 +553,14 @@ defmodule Gettext.Compiler do
     {locale, domain, singular_fun, plural_fun, quoted}
   end
 
-  defp nplurals(locale, messages_struct, plural_mod) do
-    plural_mod.nplurals(Plural.plural_info(locale, messages_struct, plural_mod))
+  defp nplurals(plural_info, plural_mod) do
+    plural_mod.nplurals(plural_info)
   end
 
-  defp compile_plural_forms(locale, messages_struct, plural_mod, plural_fun) do
+  defp compile_plural_forms(plural_info, plural_mod, plural_fun) do
     quote do
       defp unquote(plural_fun)(n) do
-        unquote(plural_mod).plural(
-          unquote(Macro.escape(Plural.plural_info(locale, messages_struct, plural_mod))),
-          n
-        )
+        unquote(plural_mod).plural(unquote(Macro.escape(plural_info)), n)
       end
     end
   end

lib/gettext/extractor.ex

@@ -462,7 +462,7 @@ defmodule Gettext.Extractor do
 
   defp read_contents_and_parse(path) do
     contents = File.read!(path)
-    {contents, PO.parse_file!(path, file: path)}
+    {contents, PO.parse_string!(contents, file: path)}
   end
 
   # This function "tags" a {path, _} tuple in order to distinguish POT files

lib/gettext/interpolation/default.ex

@@ -22,14 +22,30 @@ defmodule Gettext.Interpolation.Default do
   @doc false
   @spec to_interpolatable(String.t()) :: interpolatable()
   def to_interpolatable(string) when is_binary(string) do
-    start_pattern = :binary.compile_pattern("%{")
-    end_pattern = :binary.compile_pattern("}")
+    {start_pattern, end_pattern} = patterns()
 
     string
     |> to_interpolatable(_current = "", _acc = [], start_pattern, end_pattern)
     |> Enum.reverse()
   end
 
+  # The patterns are constant, but a compiled pattern is a reference, so it
+  # cannot be a module attribute. Compiling them on every call costs more than
+  # the split itself for short strings, so they are compiled once per VM.
+  @patterns_key {__MODULE__, :patterns}
+
+  defp patterns do
+    case :persistent_term.get(@patterns_key, nil) do
+      nil ->
+        patterns = {:binary.compile_pattern("%{"), :binary.compile_pattern("}")}
+        :persistent_term.put(@patterns_key, patterns)
+        patterns
+
+      patterns ->
+        patterns
+    end
+  end
+
   defp to_interpolatable(string, current, acc, start_pattern, end_pattern) do
     case :binary.split(string, start_pattern) do
       # If we have one element, no %{ was found so this is the final part of the