Re-Add Solidus/TaxCategoryDeprecated cop

This cop was removed earlier as it was giving a lot of false positives.

We have re-added this cop again but now with a warning offense so that it doesn't raise any errors for this cop
but warns the user to have a look at certain places in the code where something might be wrong.

config/default.yml

@@ -67,3 +67,9 @@ Solidus/SpreeTDeprecated:
   Enabled: true
   VersionAdded: '0.1.0'
   Reference: 'https://github.com/solidusio/rubocop-solidus/issues/22'
+
+Solidus/TaxCategoryDeprecated:
+  Description: 'Checks if .tax_category=Instance is being used and suggest to replace it with .tax_categories=<Array of Instances>'
+  Enabled: true
+  VersionAdded: '0.1.4'
+  Reference: 'https://github.com/solidusio/solidus/issues/1836'

lib/rubocop/cop/solidus/tax_category_deprecated.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Solidus
+      # This cop finds tax_category= usages and suggests the usage of tax_categories= instead.
+      # This cop is needed as tax_category= has been deprecated in future version.
+      #
+      # @example EnforcedStyle:
+      #   # bad
+      #   model.tax_category = data
+      #
+      #   # good
+      #   model.tax_categories = [data]
+      #
+      class TaxCategoryDeprecated < Base
+        MSG = 'tax_category= is deprecated and will be removed from Solidus 3.0. Please use tax_categories= instead. If this call is not from a Spree::TaxRate object then it is false positive.'
+
+        # @!method bad_method?(node)
+        def_node_matcher :tax_category?, <<~PATTERN
+          (send (...) :tax_category= (...))
+        PATTERN
+
+        def on_send(node)
+          return unless tax_category?(node)
+
+          add_offense(node, severity: :warning)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/solidus_cops.rb

@@ -12,3 +12,4 @@
 require_relative 'solidus/spree_icon_deprecated'
 require_relative 'solidus/spree_refund_call_perform'
 require_relative 'solidus/spree_t_deprecated'
+require_relative 'solidus/tax_category_deprecated'

spec/rubocop/cop/solidus/tax_category_deprecated_spec.rb

@@ -0,0 +1,33 @@
+
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Solidus::TaxCategoryDeprecated, :config do
+  let(:config) { RuboCop::Config.new('Solidus/TaxCategoryDeprecated' => { 'Enabled' => true }) }
+
+  it 'registers a warning when using `#.tax_category = `' do
+    expect_offense(<<~RUBY, severity: :warning)
+      model.tax_category = data
+      ^^^^^^^^^^^^^^^^^^^^^^^^^ tax_category= is deprecated and will be removed from Solidus 3.0. Please use tax_categories= instead. If this call is not from a Spree::TaxRate object then it is false positive.
+    RUBY
+  end
+
+  it 'registers a warning when using `#.tax_category =`' do
+    expect_offense(<<~RUBY, severity: :warning)
+      model.tax_category =data
+      ^^^^^^^^^^^^^^^^^^^^^^^^ tax_category= is deprecated and will be removed from Solidus 3.0. Please use tax_categories= instead. If this call is not from a Spree::TaxRate object then it is false positive.
+    RUBY
+  end
+
+  it 'registers a warning when using `#.tax_category= `' do
+    expect_offense(<<~RUBY, severity: :warning)
+      model.tax_category= data
+      ^^^^^^^^^^^^^^^^^^^^^^^^ tax_category= is deprecated and will be removed from Solidus 3.0. Please use tax_categories= instead. If this call is not from a Spree::TaxRate object then it is false positive.
+    RUBY
+  end
+
+  it 'does not register any offense when using `#.tax_categories=`' do
+    expect_no_offenses(<<~RUBY)
+      model.tax_categories = [data]
+    RUBY
+  end
+end