Install gems automatically on newer Ruby

Library/Homebrew/brew.rb

@@ -15,14 +15,6 @@
 
 std_trap = trap("INT") { exit! 130 } # no backtrace thanks
 
-# check ruby version before requiring any modules.
-REQUIRED_RUBY_X, REQUIRED_RUBY_Y, = ENV.fetch("HOMEBREW_REQUIRED_RUBY_VERSION").split(".").map(&:to_i)
-RUBY_X, RUBY_Y, = RUBY_VERSION.split(".").map(&:to_i)
-if RUBY_X < REQUIRED_RUBY_X || (RUBY_X == REQUIRED_RUBY_X && RUBY_Y < REQUIRED_RUBY_Y)
-  raise "Homebrew must be run under Ruby #{REQUIRED_RUBY_X}.#{REQUIRED_RUBY_Y}! " \
-        "You're running #{RUBY_VERSION}."
-end
-
 require_relative "global"
 
 begin

Library/Homebrew/standalone/load_path.rb

@@ -1,6 +1,14 @@
 # typed: true
 # frozen_string_literal: true
 
+# check ruby version before requiring any modules.
+required_ruby_major, required_ruby_minor, = ENV.fetch("HOMEBREW_REQUIRED_RUBY_VERSION").split(".").map(&:to_i)
+ruby_major, ruby_minor, = RUBY_VERSION.split(".").map(&:to_i)
+if ruby_major < required_ruby_major || (ruby_major == required_ruby_major && ruby_minor < required_ruby_minor)
+  raise "Homebrew must be run under Ruby #{required_ruby_major}.#{required_ruby_minor}! " \
+        "You're running #{RUBY_VERSION}."
+end
+
 # We trust base Ruby to provide what we need.
 # Don't look into the user-installed sitedir, which may contain older versions of RubyGems.
 require "rbconfig"
@@ -12,6 +20,9 @@
 require_relative "../utils/gems"
 Homebrew.setup_gem_environment!(setup_path: false)
 
+# Install gems for Rubies we don't vendor for
+Homebrew.install_bundler_gems! if ruby_major != required_ruby_major || ruby_minor != required_ruby_minor
+
 $LOAD_PATH.push HOMEBREW_LIBRARY_PATH.to_s unless $LOAD_PATH.include?(HOMEBREW_LIBRARY_PATH.to_s)
 require_relative "../vendor/bundle/bundler/setup"
 $LOAD_PATH.uniq!