(GH-118) Fail gracefully when critical gems cannot load

lib/puppet-languageserver/json_rpc_handler.rb

@@ -278,7 +278,7 @@ def reply_result(result)
       end
 
       def reply_internal_error(message = nil)
-        return nil if @json_rpc_handler.error?
+        return nil if @json_rpc_handler.connection_error?
         @json_rpc_handler.reply_error(@id, CODE_INTERNAL_ERROR, message || MSG_INTERNAL_ERROR)
       end
 

lib/puppet-languageserver/message_router.rb

@@ -247,4 +247,68 @@ def receive_notification(method, params)
       raise
     end
   end
+
+  class DisabledMessageRouter
+    attr_accessor :json_rpc_handler
+
+    def initialize(_options)
+    end
+
+    def receive_request(request)
+      case request.rpc_method
+      when 'initialize'
+        PuppetLanguageServer.log_message(:debug, 'Received initialize method')
+        # If the Language Server is not active then we can not respond to any capability. We also
+        # send a warning to the user telling them this
+        request.reply_result('capabilities' => PuppetLanguageServer::ServerCapabilites.no_capabilities)
+        # Add a minor delay before sending the notification to give the client some processing time
+        sleep(0.5)
+        @json_rpc_handler.send_show_message_notification(
+          LSP::MessageType::WARNING,
+          'An error occured while the Language Server was starting. The server has been disabled.'
+        )
+
+      when 'shutdown'
+        PuppetLanguageServer.log_message(:debug, 'Received shutdown method')
+        request.reply_result(nil)
+
+      when 'puppet/getVersion'
+        # Clients may use the getVersion request to figure out when the server has "finished" loading. In this
+        # case just fake the response that we are fully loaded with unknown gem versions
+        request.reply_result(LSP::PuppetVersion.new(
+                               'puppetVersion'   => 'Unknown',
+                               'facterVersion'   => 'Unknown',
+                               'factsLoaded'     => true,
+                               'functionsLoaded' => true,
+                               'typesLoaded'     => true,
+                               'classesLoaded'   => true
+                             ))
+
+      else
+        # For any request return an internal error.
+        request.reply_internal_error('Puppet Language Server is not active')
+        PuppetLanguageServer.log_message(:error, "Unknown RPC method #{request.rpc_method}")
+      end
+    rescue StandardError => e
+      PuppetLanguageServer::CrashDump.write_crash_file(e, nil, 'request' => request.rpc_method, 'params' => request.params)
+      raise
+    end
+
+    def receive_notification(method, params)
+      case method
+      when 'initialized'
+        PuppetLanguageServer.log_message(:info, 'Client has received initialization')
+
+      when 'exit'
+        PuppetLanguageServer.log_message(:info, 'Received exit notification.  Closing connection to client...')
+        @json_rpc_handler.close_connection
+
+      else
+        PuppetLanguageServer.log_message(:error, "Unknown RPC notification #{method}")
+      end
+    rescue StandardError => e
+      PuppetLanguageServer::CrashDump.write_crash_file(e, nil, 'notification' => method, 'params' => params)
+      raise
+    end
+  end
 end

lib/puppet-languageserver/server_capabilities.rb

@@ -17,5 +17,11 @@ def self.capabilities
         'workspaceSymbolProvider' => true
       }
     end
+
+    def self.no_capabilities
+      # Any empty hash denotes no capabilities at all
+      {
+      }
+    end
   end
 end

lib/puppet_languageserver.rb

@@ -16,9 +16,18 @@ def self.version
     PuppetEditorServices.version
   end
 
+  # Whether the language server is actually in a state that can be used.
+  # Typically this is false when a catastrophic error occurs during startup e.g. Puppet is missing.
+  #
+  # @return [Bool] Whether the language server is actually in a state that can be used
+  def self.active?
+    @server_is_active
+  end
+
   def self.require_gems(options)
     original_verbose = $VERBOSE
     $VERBOSE = nil
+    @server_is_active = false
 
     # Use specific Puppet Gem version if possible
     unless options[:puppet_version].nil?
@@ -32,16 +41,33 @@ def self.require_gems(options)
       end
     end
 
-    require 'lsp/lsp'
-    require 'puppet'
-
+    # These libraries do not require the puppet gem and required for the
+    # server to respond to clients.
     %w[
       json_rpc_handler
       document_store
       crash_dump
       message_router
-      validation_queue
       server_capabilities
+    ].each do |lib|
+      begin
+        require "puppet-languageserver/#{lib}"
+      rescue LoadError
+        require File.expand_path(File.join(File.dirname(__FILE__), 'puppet-languageserver', lib))
+      end
+    end
+
+    begin
+      require 'lsp/lsp'
+      require 'puppet'
+    rescue LoadError => e
+      log_message(:error, "Error while loading a critical gem: #{e} #{e.backtrace}")
+      return
+    end
+
+    # These libraries require the puppet and LSP gems.
+    %w[
+      validation_queue
       sidecar_protocol
       sidecar_queue
       puppet_parser_helper
@@ -57,6 +83,7 @@ def self.require_gems(options)
         require File.expand_path(File.join(File.dirname(__FILE__), 'puppet-languageserver', lib))
       end
     end
+    @server_is_active = true
   ensure
     $VERBOSE = original_verbose
   end
@@ -165,6 +192,7 @@ def self.init_puppet(options)
     log_message(:info, "Language Server is v#{PuppetEditorServices.version}")
     log_message(:debug, 'Loading gems...')
     require_gems(options)
+    return unless active?
     log_message(:info, "Using Puppet v#{Puppet.version}")
 
     log_message(:debug, "Detected additional puppet settings #{options[:puppet_settings]}")
@@ -220,6 +248,11 @@ def self.rpc_server(options)
     log_message(:info, 'Starting RPC Server...')
     options[:servicename] = 'LANGUAGE SERVER'
 
+    unless active?
+      options[:message_router] = @message_router = PuppetLanguageServer::DisabledMessageRouter.new(options)
+      log_message(:info, 'Configured the Language Server to use the Disabled Message Router')
+    end
+
     if options[:stdio]
       log_message(:debug, 'Using STDIO')
       server = PuppetEditorServices::SimpleSTDIOServer.new