Add Tapioca Addon gem RBI generation support

To support gem RBI generation, we needed a way to detect changes in
Gemfile.lock. Currently, changes to this file cause the Ruby LSP to
restart, resulting in loss of access to any previous state information.

By creating a snapshot of Gemfile.lock, we can persist data across
server restarts. Upon restart, we parse both the snapshot and current
Gemfile.lock using Bundler::LockfileParser. If differences are found,
we extract the relevant gem names and specifications, allowing us to
trigger the gem RBI generation.

lib/ruby_lsp/tapioca/addon.rb

@@ -19,6 +19,8 @@ module Tapioca
     class Addon < ::RubyLsp::Addon
       extend T::Sig
 
+      GEMFILE_LOCK_SNAPSHOT = "tmp/tapioca/.gemfile_lock_snapshot"
+
       sig { void }
       def initialize
         super
@@ -44,6 +46,8 @@ def activate(global_state, outgoing_queue)
           @rails_runner_client = addon.rails_runner_client
           outgoing_queue << Notification.window_log_message("Activating Tapioca add-on v#{version}")
           @rails_runner_client.register_server_addon(File.expand_path("server_addon.rb", __dir__))
+
+          check_gemfile_changes
         rescue IncompatibleApiError
           # The requested version for the Rails add-on no longer matches. We need to upgrade and fix the breaking
           # changes
@@ -106,6 +110,32 @@ def workspace_did_change_watched_files(changes)
           constants: constants,
         )
       end
+
+      private
+
+      sig { void }
+      def check_gemfile_changes
+        current_lockfile = File.read("Gemfile.lock")
+        snapshot_lockfile = File.read(GEMFILE_LOCK_SNAPSHOT) if File.exist?(GEMFILE_LOCK_SNAPSHOT)
+
+        unless snapshot_lockfile
+          $stdout.puts("Creating initial Gemfile.lock snapshot at #{GEMFILE_LOCK_SNAPSHOT}")
+          FileUtils.mkdir_p(File.dirname(GEMFILE_LOCK_SNAPSHOT))
+          File.write(GEMFILE_LOCK_SNAPSHOT, current_lockfile)
+          return
+        end
+
+        return if current_lockfile == snapshot_lockfile
+
+        T.must(@rails_runner_client).delegate_notification(
+          server_addon_name: "Tapioca",
+          request_name: "gem",
+          snapshot_lockfile: snapshot_lockfile,
+          current_lockfile: current_lockfile,
+        )
+
+        File.write(GEMFILE_LOCK_SNAPSHOT, current_lockfile)
+      end
     end
   end
 end

lib/ruby_lsp/tapioca/server_addon.rb

@@ -14,6 +14,8 @@ def execute(request, params)
         case request
         when "dsl"
           dsl(params)
+        when "gem"
+          gem(params)
         end
       end
 
@@ -23,6 +25,34 @@ def dsl(params)
         load("tapioca/cli.rb") # Reload the CLI to reset thor defaults between requests
         ::Tapioca::Cli.start(["dsl", "--lsp_addon", "--workers=1"] + params[:constants])
       end
+
+      def gem(params)
+        snapshot_specs = parse_lockfile(params[:snapshot_lockfile])
+        current_specs = parse_lockfile(params[:current_lockfile])
+
+        removed_gems = snapshot_specs.keys - current_specs.keys
+        changed_gems = current_specs.select { |name, version| snapshot_specs[name] != version }.keys
+
+        return $stdout.puts("No gem changes detected") if removed_gems.empty? && changed_gems.empty?
+
+        if removed_gems.any?
+          $stdout.puts("Removing RBIs for deleted gems: #{removed_gems.join(", ")}")
+          FileUtils.rm_f(Dir.glob("sorbet/rbi/gems/{#{removed_gems.join(",")}}@*.rbi"))
+        end
+
+        if changed_gems.any?
+          $stdout.puts("Generating RBIs for changed gems: #{changed_gems.join(", ")}")
+
+          load("tapioca/cli.rb") # Reload the CLI to reset thor defaults between requests
+          ::Tapioca::Cli.start(["gem"] + changed_gems)
+        end
+      end
+
+      def parse_lockfile(content)
+        return {} if content.to_s.empty?
+
+        Bundler::LockfileParser.new(content).specs.to_h { |spec| [spec.name, spec.version.to_s] }
+      end
     end
   end
 end