Lint for methods with many arguments

lib/pelusa/lint.rb

@@ -8,6 +8,7 @@
 require 'pelusa/lint/collection_wrappers'
 require 'pelusa/lint/short_identifiers'
 require 'pelusa/lint/case_statements'
+require 'pelusa/lint/many_arguments'
 
 module Pelusa
   # Public: A Lint is a quality standard, applicable on a given piece of code to
@@ -24,6 +25,7 @@ def self.all
         Properties,
         CollectionWrappers,
         ShortIdentifiers,
+        ManyArguments
       ]
     end
   end

lib/pelusa/lint/many_arguments.rb

@@ -0,0 +1,42 @@
+module Pelusa
+  module Lint
+    class ManyArguments
+      def initialize
+        @violations = Set.new
+      end
+
+      def check(klass)
+        initialize
+        iterate_lines!(klass)
+        return SuccessfulAnalysis.new(name) if @violations.empty?
+
+        FailedAnalysis.new(name, formatted_violations) do |violations|
+          "Methods with more than #{limit} arguments: #{violations.join(', ')}"
+        end
+      end
+
+      private
+
+      def name
+        "Methods have short argument lists"
+      end
+
+      def limit
+        Pelusa.configuration['ManyArguments'].fetch('limit', 3)
+      end
+
+      def iterate_lines!(klass)
+        iterator = Iterator.new do |node|
+          if node.is_a?(Rubinius::AST::Define) && node.arguments.total_args > limit
+            @violations << node.name
+          end
+        end
+        Array(klass).each(&iterator)
+      end
+
+      def formatted_violations
+        @violations.to_a
+      end
+    end
+  end
+end

test/pelusa/lint/many_arguments_test.rb

@@ -0,0 +1,47 @@
+require 'test_helper'
+
+module Pelusa
+  module Lint
+    describe ManyArguments do
+      before do
+        @lint = ManyArguments.new
+      end
+
+      describe '#check' do
+        describe 'when the class contains only method definitions with a small number of arguments' do
+          it 'returns a SuccessAnalysis' do
+            klass = """
+            class Foo
+              def bar(dog)
+                return dog
+              end
+              def baz(dog, cat)
+                return dog + cat
+              end
+              def bam(dog, cat, fish)
+                return dog + cat + fish
+              end
+            end""".to_ast
+
+            analysis = @lint.check(klass)
+            analysis.successful?.must_equal true
+          end
+        end
+
+        describe 'when the class contains a method definition with many arguments' do
+          it 'returns a FailureAnalysis' do
+            klass = """
+            class Foo
+              def bar(dog, cat, fish, lobster)
+                x = 2
+              end
+            end""".to_ast
+
+            analysis = @lint.check(klass)
+            analysis.failed?.must_equal true
+          end
+        end
+      end
+    end
+  end
+end