feat: allow easier selection of the ruby run in the container

README.md

@@ -352,6 +352,42 @@ Other environment variables can be set or passed through to the container like t
 RakeCompilerDock.sh "rake cross native gem OPENSSL_VERSION=#{ENV['OPENSSL_VERSION']}"
 ```
 
+### Choosing the version of ruby to run in the build container
+
+There are [multiple versions of Ruby installed in the build container](https://github.com/rake-compiler/rake-compiler-dock/blob/d3e6b44916d9d63d4c431b8c749a2c58bf1fe8e8/Dockerfile.mri.erb#L77). The latest version will be the default, but you may need to choose a different version to run during your build process.
+
+You can do this by passing a `ruby:` keyword argument to `RakeCompilerDock.sh`:
+
+```ruby
+RakeCompilerDock.sh "ruby -v"
+# => ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
+
+RakeCompilerDock.sh "ruby -v", ruby: "3.1.6"
+# => ruby 3.1.6p260 (2024-05-29 revision a777087be6) [x86_64-linux]48d4efcb85) +PRISM [x86_64-linux]
+```
+
+Or by setting the environment variable `RCD_RUBY_VERSION`:
+
+``` sh
+$ rake-compiler-dock bash -c "ruby -v"
+ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
+
+$ RCD_RUBY_VERSION=3.1.6 rake-compiler-dock bash -c "ruby -v"
+ruby 3.1.6p260 (2024-05-29 revision a777087be6) [x86_64-linux]
+```
+
+Or by running `rbenv shell` in the command:
+
+``` ruby
+RakeCompilerDock.sh "rbenv shell 3.1.6 && ruby -v", platform: "x86_64-linux-gnu"
+# => ruby 3.1.6p260 (2024-05-29 revision a777087be6) [x86_64-linux]
+```
+
+``` sh
+$ rake-compiler-dock bash -c "rbenv shell 3.1.6 && ruby -v"
+ruby 3.1.6p260 (2024-05-29 revision a777087be6) [x86_64-linux]
+```
+
 ### Choosing specific Ruby versions to support
 
 If you only want to precompile for certain Ruby versions, you can specify those versions by overwriting the `RUBY_CC_VERSION` environment variable.

build/sudoers

@@ -1 +1 @@
-Defaults        env_keep += "http_proxy https_proxy ftp_proxy GEM_PRIVATE_KEY_PASSPHRASE RCD_HOST_RUBY_PLATFORM RCD_HOST_RUBY_VERSION RCD_IMAGE RUBY_CC_VERSION LD_LIBRARY_PATH DEVTOOLSET_ROOTPATH SOURCE_DATE_EPOCH"
+Defaults        env_keep += "http_proxy https_proxy ftp_proxy GEM_PRIVATE_KEY_PASSPHRASE RCD_HOST_RUBY_PLATFORM RCD_HOST_RUBY_VERSION RCD_IMAGE RUBY_CC_VERSION LD_LIBRARY_PATH DEVTOOLSET_ROOTPATH SOURCE_DATE_EPOCH RBENV_VERSION"

lib/rake_compiler_dock/starter.rb

@@ -41,6 +41,11 @@ def exec(*args)
         user = options.fetch(:username){ current_user }
         group = options.fetch(:groupname){ current_group }
 
+        ruby_version = options[:ruby] || ENV['RCD_RUBY_VERSION']
+        rbenv_opts = if ruby_version
+          ["-e", "RBENV_VERSION=#{ruby_version}"]
+        end
+
         platforms(options).split(" ").each do |platform|
           image_name = container_image_name(options.merge(platform: platform))
 
@@ -73,6 +78,7 @@ def exec(*args)
               "-e", "RCD_HOST_RUBY_PLATFORM=#{RUBY_PLATFORM}",
               "-e", "RCD_HOST_RUBY_VERSION=#{RUBY_VERSION}",
               "-e", "RCD_IMAGE=#{image_name}",
+              *rbenv_opts,
               "-w", make_valid_path(workdir),
               *docker_opts,
               image_name,

test/test_environment_variables.rb

@@ -85,6 +85,19 @@ def test_SOURCE_DATE_EPOCH
     end
   end
 
+  class UsingWrapperSpecifyingRuby < UsingWrapper
+    include Common
+
+    def invocation(command)
+      idir = File.join(File.dirname(__FILE__), '../lib')
+      "RCD_RUBY_VERSION=3.1.6 RCD_PLATFORM=#{TEST_PLATFORM} RCD_RUBYVM=#{IS_JRUBY ? 'jruby' : 'mri'} #{RbConfig::CONFIG['RUBY_INSTALL_NAME']} -I#{idir.inspect} bin/rake-compiler-dock bash -c '#{command}'"
+    end
+
+    def test_RUBY_VERSION
+      assert_equal "3.1.6", rcd_env['RBENV_VERSION']
+    end
+  end
+
   class AsIfContinuousIntegration < Test::Unit::TestCase
     include Common