Fix LambdaNode ("modern" only)

lib/rubocop/ast/node/lambda_node.rb

@@ -21,7 +21,7 @@ module AST
     # The main RuboCop runs in legacy mode; this node is only used
     # if user `AST::Builder.modernize` or `AST::Builder.emit_lambda=true`
     class LambdaNode < Node
-      include ParameterizedNode
+      include ParameterizedNode::RestArguments
       include MethodDispatchNode
 
       # For similarity with legacy mode
@@ -44,14 +44,19 @@ def assignment_method?
         false
       end
 
+      # For similarity with legacy mode
+      def receiver
+        nil
+      end
+
       # For similarity with legacy mode
       def method_name
         :lambda
       end
 
       # For similarity with legacy mode
-      def arguments
-        []
+      def first_argument_index
+        2
       end
     end
   end

spec/rubocop/ast/lambda_node_spec.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+# Note: specs for `lambda?` and `lambda_literal?` in `send_node_spec`
+RSpec.describe RuboCop::AST::LambdaNode do
+  subject(:lambda_node) { parse_source(source).ast }
+
+  let(:source) { '->(a, b) { a + b }' }
+
+  describe '#receiver' do
+    it { expect(lambda_node.receiver).to eq nil }
+  end
+
+  describe '#method_name' do
+    it { expect(lambda_node.method_name).to eq :lambda }
+  end
+
+  describe '#arguments' do
+    it { expect(lambda_node.arguments.size).to eq 2 }
+  end
+end