Add a Money/UnsafeToMoney cop

README.md

@@ -156,12 +156,17 @@ require:
 
 Money/MissingCurrency:
   Enabled: true
-```
+  # If your application is currently handling only one currency,
+  # it can autocorrect this by specifying a default currency.
+  ReplacementCurrency: CAD
 
-If your application is currently handling only one currency, it can autocorrect this by specifying a currency under the `Enabled` line:
+Money/ZeroMoney:
+  Enabled: true
+  # Same here:
+  # ReplacementCurrency: CAD
 
-```yaml
-ReplacementCurrency: 'CAD'
+Money/UnsafeToMoney:
+  Enabled: true
 ```
 
 ## Contributing to money

lib/rubocop/cop/money/unsafe_to_money.rb

@@ -0,0 +1,35 @@
+
+module RuboCop
+  module Cop
+    module Money
+      # Prevents the use of `to_money` because it has inconsistent behaviour.
+      # Use `Money.new` instead.
+      #
+      # @example
+      #  # bad
+      #  "2.000".to_money("USD")     #<Money value:2000.00 currency:USD>
+      #
+      #  # good
+      #  Money.new("2.000", "USD")   #<Money value:2.00 currency:USD>
+      class UnsafeToMoney < Cop
+        MSG = '`to_money` has inconsistent behaviour. Use `Money.new` instead.'.freeze
+
+        def on_send(node)
+          return unless node.method?(:to_money)
+          return if node.receiver.is_a?(AST::NumericNode)
+
+          add_offense(node, location: :selector)
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            receiver = node.receiver.source
+            args = node.arguments.map(&:source)
+            args.prepend(receiver)
+            corrector.replace(node.loc.expression, "Money.new(#{args.join(', ')})")
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/money/unsafe_to_money_spec.rb

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+require_relative '../../../rubocop_helper'
+require 'rubocop/cop/money/unsafe_to_money'
+
+RSpec.describe RuboCop::Cop::Money::UnsafeToMoney do
+  subject(:cop) { described_class.new(config) }
+
+  let(:config) { RuboCop::Config.new }
+
+  context 'with default configuration' do
+    it 'does not register an offense for literal integer' do
+      expect_no_offenses(<<~RUBY)
+        1.to_money
+      RUBY
+    end
+
+    it 'does not register an offense for literal float' do
+      expect_no_offenses(<<~RUBY)
+        1.000.to_money
+      RUBY
+    end
+
+    it 'registers an offense and corrects for Money.new without a currency argument' do
+      expect_offense(<<~RUBY)
+        '2.000'.to_money
+                ^^^^^^^^ #{described_class::MSG}
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Money.new('2.000')
+      RUBY
+    end
+
+    it 'registers an offense and corrects for Money.new with a currency argument' do
+      expect_offense(<<~RUBY)
+        '2.000'.to_money('USD')
+                ^^^^^^^^ #{described_class::MSG}
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Money.new('2.000', 'USD')
+      RUBY
+    end
+
+    it 'registers an offense and corrects for Money.new with a complex receiver' do
+      expect_offense(<<~RUBY)
+        obj.money.to_money('USD')
+                  ^^^^^^^^ #{described_class::MSG}
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Money.new(obj.money, 'USD')
+      RUBY
+    end
+  end
+end