bottle: reproducibility fixes.

I noticed from
https://github.com/Homebrew/homebrew-core/actions/runs/5751070010 that
we're no longer creating reproducible bottles between macOS and Linux.

All macOS checksums have changed but Linux ones have not. The main
difference between the two platforms is the `gtar` version used so let's
always just use the formula on both platforms.

While we're here, clear up the ordering and comments a little on the
reproducible `tar` arguments so that it's easier to compare with the
reproducible builds archives documentation.

.github/workflows/tests.yml

@@ -428,4 +428,6 @@ jobs:
 
       - run: brew test-bot --only-setup
 
+      - run: brew install gnu-tar
+
       - run: brew test-bot --only-formulae --only-json-tab --test-default-formula

Library/Homebrew/dev-cmd/bottle.rb

@@ -234,14 +234,26 @@ module Homebrew
     [].freeze
   end
 
+  sig { params(gnu_tar_formula: Formula).returns(String) }
+  def self.gnu_tar(gnu_tar_formula)
+    "#{gnu_tar_formula.opt_bin}/tar"
+  end
+
   sig { params(mtime: String).returns(T::Array[String]) }
   def self.reproducible_gnutar_args(mtime)
     # Ensure gnu tar is set up for reproducibility.
     # https://reproducible-builds.org/docs/archives/
     [
-      "--format", "pax", "--owner", "0", "--group", "0", "--sort", "name", "--mtime=#{mtime}",
+      # File modification times
+      "--mtime=#{mtime}",
+      # File ordering
+      "--sort=name",
+      # Users, groups and numeric ids
+      "--owner=0", "--group=0", "--numeric-owner",
+      # PAX headers
+      "--format=pax",
       # Set exthdr names to exclude PID (for GNU tar <1.33). Also don't store atime and ctime.
-      "--pax-option", "globexthdr.name=/GlobalHead.%n,exthdr.name=%d/PaxHeaders/%f,delete=atime,delete=ctime"
+      "--pax-option=globexthdr.name=/GlobalHead.%n,exthdr.name=%d/PaxHeaders/%f,delete=atime,delete=ctime"
     ].freeze
   end
 
@@ -253,14 +265,14 @@ module Homebrew
 
     # Use gnu-tar as it can be set up for reproducibility better than libarchive.
     begin
-      gnu_tar = Formula["gnu-tar"]
+      gnu_tar_formula = Formula["gnu-tar"]
     rescue FormulaUnavailableError
       return default_tar_args
     end
 
-    ensure_formula_installed!(gnu_tar, reason: "bottling")
+    ensure_formula_installed!(gnu_tar_formula, reason: "bottling")
 
-    ["#{gnu_tar.opt_bin}/gtar", reproducible_gnutar_args(mtime)].freeze
+    [gnu_tar(gnu_tar_formula), reproducible_gnutar_args(mtime)].freeze
   end
 
   def self.formula_ignores(formula)

Library/Homebrew/extend/os/dev-cmd/bottle.rb

@@ -1,8 +1,4 @@
 # typed: strict
 # frozen_string_literal: true
 
-if OS.mac?
-  require "extend/os/mac/dev-cmd/bottle"
-elsif OS.linux?
-  require "extend/os/linux/dev-cmd/bottle"
-end
+require "extend/os/mac/dev-cmd/bottle" if OS.mac?

Library/Homebrew/extend/os/linux/dev-cmd/bottle.rb

@@ -1,12 +0,0 @@
-# typed: true
-# frozen_string_literal: true
-
-module Homebrew
-  sig { params(args: T.untyped, mtime: String).returns([String, T::Array[String]]) }
-  def self.setup_tar_and_args!(args, mtime)
-    # Without --only-json-tab bottles are never reproducible
-    return ["tar", tar_args].freeze unless args.only_json_tab?
-
-    ["tar", reproducible_gnutar_args(mtime)].freeze
-  end
-end

Library/Homebrew/extend/os/mac/dev-cmd/bottle.rb

@@ -10,4 +10,9 @@ module Homebrew
       [].freeze
     end
   end
+
+  sig { params(gnu_tar_formula: Formula).returns(String) }
+  def self.gnu_tar(gnu_tar_formula)
+    "#{gnu_tar_formula.opt_bin}/gtar"
+  end
 end