feat: support registering system Ruby

.github/workflows/ci.yml

@@ -34,6 +34,7 @@ jobs:
           - 3.3.0-preview3
           - jruby-9.4.5.0
           - truffleruby-23.1.1
+          - system
         os:
           - ubuntu
           - macos
@@ -49,6 +50,8 @@ jobs:
           - os: windows
             ruby: truffleruby-23.1.1
           # https://github.com/p0deje/rules_ruby/issues/23
+          - mode: bzlmod
+            ruby: system
           - mode: bzlmod
             ruby: 3.0.6
           - mode: bzlmod
@@ -72,6 +75,10 @@ jobs:
             build --announce_rc
             ${{ matrix.mode == 'bzlmod' && 'common --enable_bzlmod' || '' }}
       - run: echo 'RUBY_VERSION = "${{ matrix.ruby }}"' > ruby_version.bzl
+      - if: matrix.ruby == 'system'
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.0.6'
       - run: bazel test ...
       - run: bazel run lib/gem:add-numbers 2
       - run: bazel run lib/gem:print-version

ruby/private/download.bzl

@@ -6,6 +6,8 @@ _RUBY_INSTALLER_URL = "https://github.com/oneclick/rubyinstaller2/releases/downl
 def _rb_download_impl(repository_ctx):
     if repository_ctx.attr.version.startswith("jruby"):
         _install_jruby(repository_ctx)
+    elif repository_ctx.attr.version == "system":
+        _symlink_system_ruby(repository_ctx)
     elif repository_ctx.os.name.startswith("windows"):
         _install_via_rubyinstaller(repository_ctx)
     else:
@@ -94,6 +96,14 @@ def _install_via_ruby_build(repository_ctx):
     if result.return_code != 0:
         fail("%s\n%s" % (result.stdout, result.stderr))
 
+def _symlink_system_ruby(repository_ctx):
+    repository_ctx.symlink(repository_ctx.which("ruby"), "dist/bin/ruby")
+    repository_ctx.symlink(repository_ctx.which("gem"), "dist/bin/gem")
+    if repository_ctx.os.name.startswith("windows"):
+        repository_ctx.symlink(repository_ctx.which("bundle.cmd"), "dist/bin/bundle.cmd")
+    else:
+        repository_ctx.symlink(repository_ctx.which("bundle"), "dist/bin/bundle")
+
 rb_download = repository_rule(
     implementation = _rb_download_impl,
     attrs = {

ruby/private/toolchain.bzl

@@ -13,6 +13,7 @@ def rb_register_toolchains(name = DEFAULT_RUBY_REPOSITORY, version = None, regis
     * _(For MRI on Windows)_ Installed using [RubyInstaller](https://rubyinstaller.org).
     * _(For JRuby on any OS)_ Downloaded and installed directly from [official website](https://www.jruby.org).
     * _(For TruffleRuby on Linux and macOS)_ Installed using [ruby-build](https://github.com/rbenv/ruby-build).
+    * _(For "system") System Ruby is used. Please note that builds are not hermetic in this case.
 
     `WORKSPACE`:
     ```bazel
@@ -25,14 +26,18 @@ def rb_register_toolchains(name = DEFAULT_RUBY_REPOSITORY, version = None, regis
 
     Args:
         name: base name of resulting repositories, by default "rules_ruby"
-        version: a semver version of Matz Ruby Interpreter, or a string like [interpreter type]-[version]
+        version: a semver version of Matz Ruby Interpreter, or a string like [interpreter type]-[version], or "system"
         register: whether to register the resulting toolchains, should be False under bzlmod
         **kwargs: additional parameters to the downloader for this interpreter type
     """
     repo_name = name + "_dist"
     proxy_repo_name = name + "_toolchains"
     if repo_name not in native.existing_rules().values():
-        _rb_download(name = repo_name, version = version, **kwargs)
+        _rb_download(
+            name = repo_name,
+            version = version,
+            **kwargs
+        )
         _rb_toolchain_repository_proxy(
             name = proxy_repo_name,
             toolchain = "@{}//:toolchain".format(repo_name),