Retry composing bundle if it's modified during setup (#2890)

### Motivation

If someone switches branches while we're setting up the composed bundle and the switch results in gemfile/lockfile changes, we often fail to boot because the resulting bundle is invalid.

### Implementation

I think we can reduce the number of failures by checking if the contents of the gemfile or lockfile have been changed after we finished running bundle install. If that's the case, we can re-build the composed bundle from scratch and retry a single time, which should be able to fix common issues.

### Automated Tests

Added a test that verifies the new behaviour.

Author: vinistock

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)