Add ChefStyle/UsePlatformHelpers cop

Move people towards our platform? and platform_family? helpers to simplify the platform checks in their recipes / resources.

Signed-off-by: Tim Smith <tsmith@chef.io>

config/cookstyle.yml

@@ -63,6 +63,14 @@ ChefStyle/FileMode:
   Exclude:
     - '**/metadata.rb'
 
+ChefStyle/UsePlatformHelpers:
+  Description: Use platform? and platform_family? helpers for checking node platform in resources and recipes
+  Enabled: true
+  VersionAdded: '5.6.0'
+  Exclude:
+    - '**/metadata.rb'
+    - '**/libraries/*'
+
 ###############################
 # ChefCorrectness: Avoiding potential problems
 ###############################

lib/rubocop/cop/chef/style/use_platform_helpers.rb

@@ -0,0 +1,59 @@
+#
+# Copyright:: 2019, Chef Software, Inc.
+# Author:: Tim Smith (<tsmith@chef.io>)
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+module RuboCop
+  module Cop
+    module Chef
+      module ChefStyle
+        # Use the platform?() and platform_family?() helpers instead of node['platform] == 'foo'
+        # and node['platform_family'] == 'bar'. These helpers are easier to read and can accept multiple
+        # platform arguments, which greatly simplifies complex platform logic.
+        #
+        # @example
+        #
+        #   # bad
+        #   node['platform'] == 'ubuntu'
+        #
+        #   # good
+        #   platform?('ubuntu')
+        #
+        class UsePlatformHelpers < Cop
+          MSG = "Use platform? and platform_family? helpers for checking node platform".freeze
+
+          def_node_matcher :platform_check?, <<-PATTERN
+            ( send (send (send nil? :node) :[] $(str {"platform" "platform_family"}) ) :== $str )
+          PATTERN
+
+          def on_send(node)
+            platform_check?(node) do |type, plat|
+              # set these so we can use them in the auto_correct method
+              @type = type
+              @plat = plat
+
+              add_offense(node, location: :expression, message: MSG, severity: :refactor)
+            end
+          end
+
+          def autocorrect(node)
+            lambda do |corrector|
+              corrector.replace(node.loc.expression, "#{@type.value}?('#{@plat.value}')")
+            end
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/chef/style/use_platform_helpers_spec.rb

@@ -0,0 +1,47 @@
+#
+# Copyright:: 2019, Chef Software, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require 'spec_helper'
+
+describe RuboCop::Cop::Chef::ChefStyle::UsePlatformHelpers do
+  subject(:cop) { described_class.new }
+
+  it "registers an offense when checking platform using node['platform']" do
+    expect_offense(<<~RUBY)
+      if node['platform'] == 'redhat'
+         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use platform? and platform_family? helpers for checking node platform
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      if platform?('redhat')
+      end
+    RUBY
+  end
+
+  it "registers an offense when checking platform family using node['platform_family']" do
+    expect_offense(<<~RUBY)
+      if node['platform_family'] == 'rhel'
+         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use platform? and platform_family? helpers for checking node platform
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      if platform_family?('rhel')
+      end
+    RUBY
+  end
+end