Print Bundler progress to stderr when invoking CLI directly

lib/ruby_lsp/setup_bundler.rb

@@ -32,6 +32,7 @@ def initialize(project_path, **options)
       @project_path = project_path
       @branch = T.let(options[:branch], T.nilable(String))
       @launcher = T.let(options[:launcher], T.nilable(T::Boolean))
+      patch_thor_to_print_progress_to_stderr! if @launcher
 
       # Regular bundle paths
       @gemfile = T.let(
@@ -400,5 +401,21 @@ def base_bundle_command(env)
 
       "bundle"
     end
+
+    sig { void }
+    def patch_thor_to_print_progress_to_stderr!
+      return unless defined?(Bundler::Thor::Shell::Basic)
+
+      Bundler::Thor::Shell::Basic.prepend(Module.new do
+        extend T::Sig
+
+        sig { returns(IO) }
+        def stdout
+          $stderr
+        end
+      end)
+
+      Bundler.ui.level = :info
+    end
   end
 end

project-words

@@ -27,6 +27,7 @@ FIXEDENCODING
 Floo
 fnmatch
 fooo
+gemname
 hostedtoolcache
 importmap
 indexables

sorbet/rbi/shims/bundler.rbi

@@ -23,4 +23,10 @@ module Bundler
       def run; end
     end
   end
+
+  module Thor # rubocop:disable Style/ClassAndModuleChildren
+    module Shell
+      class Basic; end
+    end
+  end
 end

test/setup_bundler_test.rb

@@ -714,6 +714,31 @@ def test_invoke_cli_calls_bundler_directly_for_update
     end
   end
 
+  def test_progress_is_printed_to_stderr
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        File.write(File.join(dir, "Gemfile"), <<~GEMFILE)
+          source "https://rubygems.org"
+          gem "rdoc"
+        GEMFILE
+
+        Bundler.with_unbundled_env do
+          capture_subprocess_io do
+            # Run bundle install to generate the lockfile
+            system("bundle install")
+          end
+
+          stdout, stderr = capture_subprocess_io do
+            RubyLsp::SetupBundler.new(dir, launcher: true).setup!
+          end
+
+          assert_match(/Bundle complete! [\d]+ Gemfile dependencies, [\d]+ gems now installed/, stderr)
+          assert_empty(stdout)
+        end
+      end
+    end
+  end
+
   private
 
   def with_default_external_encoding(encoding, &block)