[rubygems/rubygems] Fix Ruby DSL no longer working as expected

https://github.com/rubygems/rubygems/commit/f6258e5679

Co-authored-by: AndrewSwerlick <andrew.swerlick@gmail.com>

lib/bundler/dsl.rb

@@ -20,7 +20,7 @@ module Bundler
 
     GITHUB_PULL_REQUEST_URL = %r{\Ahttps://github\.com/([A-Za-z0-9_\-\.]+/[A-Za-z0-9_\-\.]+)/pull/(\d+)\z}
 
-    attr_reader :gemspecs
+    attr_reader :gemspecs, :gemfile
     attr_accessor :dependencies
 
     def initialize

spec/bundler/install/gemfile/ruby_spec.rb

@@ -120,4 +120,38 @@ RSpec.describe "ruby requirement" do
 
     expect(err).to include("There was an error parsing") # i.e. DSL error, not error template
   end
+
+  it "allows picking up ruby version from a file" do
+    create_file ".ruby-version", Gem.ruby_version.to_s
+
+    install_gemfile <<-G
+      source "#{file_uri_for(gem_repo1)}"
+      ruby file: ".ruby-version"
+      gem "rack"
+    G
+
+    expect(lockfile).to include("RUBY VERSION")
+  end
+
+  it "reads the ruby version file from the right folder when nested Gemfiles are involved" do
+    create_file ".ruby-version", Gem.ruby_version.to_s
+
+    gemfile <<-G
+      source "#{file_uri_for(gem_repo1)}"
+      ruby file: ".ruby-version"
+      gem "rack"
+    G
+
+    nested_dir = bundled_app(".ruby-lsp")
+
+    FileUtils.mkdir nested_dir
+
+    create_file ".ruby-lsp/Gemfile", <<-G
+      eval_gemfile(File.expand_path("../Gemfile", __dir__))
+    G
+
+    bundle "install", dir: nested_dir
+
+    expect(bundled_app(".ruby-lsp/Gemfile.lock").read).to include("RUBY VERSION")
+  end
 end