Retry composing bundle if it's modified during setup

lib/ruby_lsp/setup_bundler.rb

@@ -45,6 +45,9 @@ def initialize(project_path, **options)
       )
       @lockfile = T.let(@gemfile ? Bundler.default_lockfile : nil, T.nilable(Pathname))
 
+      @gemfile_hash = T.let(@gemfile ? Digest::SHA256.hexdigest(@gemfile.read) : nil, T.nilable(String))
+      @lockfile_hash = T.let(@lockfile&.exist? ? Digest::SHA256.hexdigest(@lockfile.read) : nil, T.nilable(String))
+
       @gemfile_name = T.let(@gemfile&.basename&.to_s || "Gemfile", String)
 
       # Custom bundle paths
@@ -91,10 +94,8 @@ def setup!
         return run_bundle_install(@custom_gemfile)
       end
 
-      lockfile_contents = @lockfile.read
-      current_lockfile_hash = Digest::SHA256.hexdigest(lockfile_contents)
-
-      if @custom_lockfile.exist? && @lockfile_hash_path.exist? && @lockfile_hash_path.read == current_lockfile_hash
+      if @lockfile_hash && @custom_lockfile.exist? && @lockfile_hash_path.exist? &&
+          @lockfile_hash_path.read == @lockfile_hash
         $stderr.puts(
           "Ruby LSP> Skipping composed bundle setup since #{@custom_lockfile} already exists and is up to date",
         )
@@ -103,7 +104,7 @@ def setup!
 
       FileUtils.cp(@lockfile.to_s, @custom_lockfile.to_s)
       correct_relative_remote_paths
-      @lockfile_hash_path.write(current_lockfile_hash)
+      @lockfile_hash_path.write(@lockfile_hash)
       run_bundle_install(@custom_gemfile)
     end
 
@@ -214,6 +215,23 @@ def run_bundle_install(bundle_gemfile = @gemfile)
         @error_path.write(Marshal.dump(e))
       end
 
+      # If either the Gemfile or the lockfile have been modified during the process of setting up the bundle, retry
+      # composing the bundle from scratch
+
+      if @gemfile && @lockfile
+        current_gemfile_hash = Digest::SHA256.hexdigest(@gemfile.read)
+        current_lockfile_hash = Digest::SHA256.hexdigest(@lockfile.read)
+
+        if !@retry && (current_gemfile_hash != @gemfile_hash || current_lockfile_hash != @lockfile_hash)
+          @gemfile_hash = current_gemfile_hash
+          @lockfile_hash = current_lockfile_hash
+          @retry = true
+          @custom_dir.rmtree
+          $stderr.puts("Ruby LSP> Bundle was modified during setup. Retrying from scratch...")
+          return setup!
+        end
+      end
+
       env
     end
 

test/setup_bundler_test.rb

@@ -786,6 +786,43 @@ def test_succeeds_when_using_ssh_git_sources_instead_of_https
     end
   end
 
+  def test_is_resilient_to_gemfile_changes_in_the_middle_of_setup
+    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")
+
+            # This section simulates the bundle being modified during the composed bundle setup. We initialize the
+            # composed bundle first to eagerly calculate the gemfile and lockfile hashes. Then we modify the Gemfile
+            # afterwards and trigger the setup.
+            #
+            # This type of scenario may happen if someone switches branches in the middle of running bundle install. By
+            # the time we finish, the bundle may be in a different state and we need to recover from that
+            composed_bundle = RubyLsp::SetupBundler.new(dir, launcher: true)
+
+            File.write(File.join(dir, "Gemfile"), <<~GEMFILE)
+              source "https://rubygems.org"
+              gem "rdoc"
+              gem "irb"
+            GEMFILE
+            system("bundle install")
+
+            composed_bundle.setup!
+          end
+
+          assert_match("irb", File.read(".ruby-lsp/Gemfile.lock"))
+        end
+      end
+    end
+  end
+
   private
 
   def with_default_external_encoding(encoding, &block)