Workaround macOS system Ruby issue picking incorrect native gem archs

Library/Homebrew/rubyext/rubygems/defaults/operating_system.rb

@@ -0,0 +1,20 @@
+# typed: strict
+# frozen_string_literal: true
+
+require "etc"
+
+# Fixes universal-ruby getting confused whether to install arm64 or x86_64 macOS versions.
+# https://github.com/rubygems/rubygems/issues/4234
+# This can be removed when either:
+# - We stop using system Ruby
+# - System Ruby is updated with this patch (shipped with Ruby 3.1 or later):
+#   https://github.com/ruby/ruby/commit/96ce1d9a0ff64494753ad4730f36a0cd7e7a89e7
+# - The Rubygems PR https://github.com/rubygems/rubygems/pull/4238 is merged
+#   AND we install a new enough Rubygems which includes the said patch, instead of relying the system's version.
+platform = Gem::Platform.local.dup
+platform.cpu = Etc.uname[:machine] if platform.os == "darwin" && platform.cpu == "universal"
+Gem.platforms[Gem.platforms.index(Gem::Platform.local)] = platform
+
+# This doesn't currently exist in system Ruby but it's safer to check.
+orig_file = File.join(RbConfig::CONFIG["rubylibdir"], "rubygems", "defaults", "operating_system")
+require orig_file if File.exist?(orig_file)

Library/Homebrew/shims/ruby/bundle

@@ -0,0 +1,15 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+# Insert our system Ruby patch script, if neeeded.
+# Fixes universal-ruby getting confused whether to install arm64 or x86_64 macOS versions.
+# https://github.com/rubygems/rubygems/issues/4234
+if RUBY_PLATFORM.match?(/universal\..*-darwin/)
+  rubylib = File.expand_path("../../rubyext", File.dirname(__FILE__))
+  ENV["RUBYLIB"] = rubylib
+  $LOAD_PATH.unshift(rubylib) unless $LOAD_PATH.include?(rubylib)
+  require "rubygems/defaults/operating_system" if defined?(Gem) # Reload if already loaded.
+end
+
+require "rubygems"
+load Gem.activate_bin_path("bundler", "bundle", ">= 0.a")

Library/Homebrew/style.rb

@@ -263,7 +263,11 @@ module Homebrew
         HOMEBREW_REPOSITORY/"Dockerfile",
         *HOMEBREW_LIBRARY.glob("Homebrew/*.sh"),
         *HOMEBREW_LIBRARY.glob("Homebrew/shims/**/*").map(&:realpath).uniq
-                         .reject { |path| path.directory? || path.basename.to_s == "cc" },
+                         .reject(&:directory?)
+                         .reject { |path| path.basename.to_s == "cc" }
+                         .select do |path|
+                           %r{^#! ?/bin/(?:ba)?sh( |$)}.match?(path.read(13)) || path.extname == ".sh"
+                         end,
         *HOMEBREW_LIBRARY.glob("Homebrew/{dev-,}cmd/*.sh"),
         *HOMEBREW_LIBRARY.glob("Homebrew/{cask/,}utils/*.sh"),
       ]

Library/Homebrew/utils/gems.rb

@@ -60,6 +60,7 @@ module Homebrew
     paths = ENV.fetch("PATH").split(":")
     paths.unshift(ruby_bindir) unless paths.include?(ruby_bindir)
     paths.unshift(Gem.bindir) unless paths.include?(Gem.bindir)
+    paths.unshift(HOMEBREW_SHIMS_PATH/"ruby") unless paths.include?(HOMEBREW_SHIMS_PATH/"ruby")
     ENV["PATH"] = paths.compact.join(":")
 
     # Set envs so the above binaries can be invoked.