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 running git diff on Gemfile.lock, we can detect changes to the file,
and trigger the gem RBI generation process.

Then we can parse the diff output to determine which gems have been
removed, added or modified, and either remove the corresponding RBI
files or trigger the RBI generation process for the gems.

lib/ruby_lsp/tapioca/addon.rb

@@ -27,6 +27,7 @@ def initialize
         @rails_runner_client = T.let(nil, T.nilable(RubyLsp::Rails::RunnerClient))
         @index = T.let(nil, T.nilable(RubyIndexer::Index))
         @file_checksums = T.let({}, T::Hash[String, String])
+        @lockfile_diff = T.let(nil, T.nilable(String))
         @outgoing_queue = T.let(nil, T.nilable(Thread::Queue))
       end
 
@@ -45,6 +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__))
+
+          generate_gem_rbis if git_repo? && lockfile_changed?
         rescue IncompatibleApiError
           # The requested version for the Rails add-on no longer matches. We need to upgrade and fix the breaking
           # changes
@@ -127,6 +130,30 @@ def file_updated?(change, path)
 
         false
       end
+
+      sig { returns(T::Boolean) }
+      def git_repo?
+        Dir.exist?(".git")
+      end
+
+      sig { returns(T::Boolean) }
+      def lockfile_changed?
+        !fetch_lockfile_diff.empty?
+      end
+
+      sig { returns(String) }
+      def fetch_lockfile_diff
+        @lockfile_diff = %x(git diff HEAD Gemfile.lock).strip
+      end
+
+      sig { void }
+      def generate_gem_rbis
+        T.must(@rails_runner_client).delegate_notification(
+          server_addon_name: "Tapioca",
+          request_name: "gem",
+          diff: T.must(@lockfile_diff),
+        )
+      end
     end
   end
 end

lib/ruby_lsp/tapioca/server_addon.rb

@@ -2,6 +2,7 @@
 # frozen_string_literal: true
 
 require "tapioca/internal"
+require_relative "lockfile_diff_parser"
 
 module RubyLsp
   module Tapioca
@@ -16,6 +17,8 @@ def execute(request, params)
           fork do
             dsl(params)
           end
+        when "gem"
+          gem(params)
         end
       end
 
@@ -25,6 +28,20 @@ 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)
+        gem_changes = LockfileDiffParser.new(params[:diff])
+
+        removed_gems = gem_changes.removed_gems
+        added_or_modified_gems = gem_changes.added_or_modified_gems
+
+        if added_or_modified_gems.any?
+          load("tapioca/cli.rb") # Reload the CLI to reset thor defaults between requests
+          ::Tapioca::Cli.start(["gem"] + added_or_modified_gems)
+        elsif removed_gems.any?
+          FileUtils.rm_f(Dir.glob("sorbet/rbi/gems/{#{removed_gems.join(",")}}@*.rbi"))
+        end
+      end
     end
   end
 end