Prevent rake compiler from defining application defined task:

lib/cibuildgem/cli.rb

@@ -137,8 +137,13 @@ def run_rake_tasks!(*tasks)
       rake_path = rake_specs.full_require_paths
       prism_path = Gem.loaded_specs["prism"].full_require_paths
       load_paths = (rake_compiler_path + rake_path + prism_path).join(File::PATH_SEPARATOR)
+      patch = File.expand_path("../extension_patch.rb", __FILE__)
 
-      system({ "RUBYLIB" => load_paths }, "bundle exec #{RbConfig.ruby} #{rake_executable} #{all_tasks} -R#{rakelibdir}", exception: true)
+      system(
+        { "RUBYLIB" => load_paths },
+        "bundle exec #{RbConfig.ruby} #{rake_executable} #{all_tasks} -R#{rakelibdir} -r #{patch}",
+        exception: true,
+      )
     end
 
     def compilation_task

lib/cibuildgem/compilation_tasks.rb

@@ -17,6 +17,8 @@ def initialize(create_packaging_task = false, gemspec = nil)
     end
 
     def setup
+      Rake::ExtensionTask.enable!
+
       gemspec.extensions.each do |path|
         binary_name = parse_extconf(path)
         define_task(path, binary_name)

lib/cibuildgem/extension_patch.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require "rake/extensiontask"
+
+module Cibuildgem
+  module ExtensionPatch
+    class << self
+      def prepended(mod)
+        class << mod
+          attr_accessor :enabled
+
+          def enable!
+            @enabled = true
+          end
+        end
+      end
+    end
+
+    def define
+      super if self.class.enabled
+    end
+  end
+end
+
+Rake::ExtensionTask.prepend(Cibuildgem::ExtensionPatch)

test/cli_test.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "test_helper"
+require "English"
 
 module Cibuildgem
   class CLITest < Minitest::Test
@@ -214,6 +215,14 @@ def test_cli_test_command_when_no_test_or_spec_rake_task_is_defined
       end
     end
 
+    def test_package_when_a_rakefile_defines_an_extension_task
+      Dir.chdir("test/fixtures/with_ext") do
+        CLI.start(["package"])
+      end
+
+      assert_predicate($CHILD_STATUS, :success?)
+    end
+
     private
 
     def raise_instead_of_exit(&block)

test/fixtures/with_ext/Rakefile

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+require "rake/extensiontask"
+
+gemspec = Gem::Specification.load("foo.gemspec")
+Rake::ExtensionTask.new("foo", gemspec)
+
+raise "No rake task should have been defined" if Rake::Task.task_defined?(:native)
+
+exit(0)

test/fixtures/with_ext/foo.gemspec

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+Gem::Specification.new do |spec|
+  spec.name = "edouard-dummy_gem"
+  spec.version = "0.0.1"
+  spec.authors = ["Edouard CHIN"]
+  spec.email = ["user@example.org"]
+  spec.summary = "A gem that do nothing"
+  spec.description = "Don't use it, really."
+  spec.license = "MIT"
+  spec.files = []
+  spec.require_paths = ["lib"]
+  spec.extensions = ["ext/hello_world/extconf.rb"]
+end