rails new: add x86_64-linux and aarch64-linux platforms by default

Ref: rails#47479

The vast majority of apps will be deployed on Linux, so might as
well initialize the Gemfile.lock with these platforms. This will
save users from having to do it themselves when they push to
GitHub Actions or similar platforms.

Author: byroot

railties/lib/rails/generators/app_base.rb

@@ -644,7 +644,17 @@ def target_rails_prerelease(self_command = "new")
       end
 
       def run_bundle
-        bundle_command("install", "BUNDLE_IGNORE_MESSAGES" => "1") if bundle_install?
+        if bundle_install?
+          bundle_command("install", "BUNDLE_IGNORE_MESSAGES" => "1")
+
+          # The vast majority of Rails apps will be deployed on `x86_64-linux`.
+          platform = ["--add-platform=x86_64-linux"]
+
+          # Users that develop on M1 mac may use docker and would need `aarch64-linux` as well.
+          platform << "--add-platform=aarch64-linux" if RUBY_PLATFORM.start_with?("arm64")
+
+          bundle_command("lock #{platform.join(" ")}", "BUNDLE_IGNORE_MESSAGES" => "1")
+        end
       end
 
       def run_javascript

railties/test/generators/shared_generator_tests.rb

@@ -366,9 +366,11 @@ def run_generator_using_prerelease(args)
 
       assert_file File.expand_path("Gemfile", project_path) do |gemfile|
         assert_equal "install", @bundle_commands[0]
+        assert_match "lock --add-platform", @bundle_commands[1]
+
         assert_equal gemfile[rails_gem_pattern], bundle_command_rails_gems[0]
 
-        assert_match %r"^exec rails (?:plugin )?new #{Regexp.escape Shellwords.join(expected_args)}", @bundle_commands[1]
+        assert_match %r"^exec rails (?:plugin )?new #{Regexp.escape Shellwords.join(expected_args)}", @bundle_commands[2]
         assert_equal gemfile[rails_gem_pattern], bundle_command_rails_gems[1]
       end
     end