Add #to_d support to BigDecimalWithNumericArgument

The [`bigdecimal/util`](https://github.com/ruby/bigdecimal/blob/v3.0.2/lib/bigdecimal/util.rb)
library adds `#to_d` to several numeric types, where

```ruby
numeric.to_d(*args)
```

is equivalent to

```ruby
BigDecimal(numeric, *args)
```

and the performance improvement of `BigDecimalWithNumericArgument`
therefore equally applies here.

CHANGELOG.md

@@ -312,3 +312,4 @@
 [@ghiculescu]: https://github.com/ghiculescu
 [@mfbmina]: https://github.com/mfbmina
 [@mvz]: https://github.com/mvz
+[@leoarnold]: https://github.com/leoarnold

changelog/new_add_to_d_to_BigDecimalWithNumericArgument.md

@@ -0,0 +1 @@
+* [#269](https://github.com/rubocop/rubocop-performance/pull/269): Add `#to_d` support to `BigDecimalWithNumericArgument`. ([@leoarnold][])

config/default.yml

@@ -17,7 +17,7 @@ Performance/ArraySemiInfiniteRangeSlice:
   VersionAdded: '1.9'
 
 Performance/BigDecimalWithNumericArgument:
-  Description: 'Convert numeric argument to string before passing to BigDecimal.'
+  Description: 'Convert numeric literal to string and pass it to `BigDecimal`.'
   Enabled: 'pending'
   VersionAdded: '1.7'
 

lib/rubocop/cop/performance/big_decimal_with_numeric_argument.rb

@@ -10,35 +10,62 @@ module Performance
       # @example
       #   # bad
       #   BigDecimal(1, 2)
-      #   BigDecimal(1.2, 3, exception: true)
+      #   1.to_d(2)
+      #   BigDecimal(1.2, exception: true)
+      #   1.2.to_d(exception: true)
       #
       #   # good
       #   BigDecimal('1', 2)
-      #   BigDecimal('1.2', 3, exception: true)
+      #   BigDecimal('1.2', exception: true)
       #
       class BigDecimalWithNumericArgument < Base
         extend AutoCorrector
 
-        MSG = 'Convert numeric argument to string before passing to `BigDecimal`.'
-        RESTRICT_ON_SEND = %i[BigDecimal].freeze
+        MSG = 'Convert numeric literal to string and pass it to `BigDecimal`.'
+        RESTRICT_ON_SEND = %i[BigDecimal to_d].freeze
 
         def_node_matcher :big_decimal_with_numeric_argument?, <<~PATTERN
           (send nil? :BigDecimal $numeric_type? ...)
         PATTERN
 
+        def_node_matcher :to_d?, <<~PATTERN
+          (send [!nil? $numeric_type?] :to_d ...)
+        PATTERN
+
         def on_send(node)
-          return unless (numeric = big_decimal_with_numeric_argument?(node))
-          return if numeric.float_type? && specifies_precision?(node)
+          if (numeric = big_decimal_with_numeric_argument?(node))
+            on_send_big_decimal(node, numeric)
+          elsif (numeric_to_d = to_d?(node))
+            on_send_to_d(node, numeric_to_d)
+          end
+        end
+
+        private
+
+        def on_send_big_decimal(node, numeric)
+          return if numeric.float_type? && specifies_precision?(node, position: 1)
 
           add_offense(numeric.source_range) do |corrector|
             corrector.wrap(numeric, "'", "'")
           end
         end
 
-        private
+        def on_send_to_d(node, numeric_to_d)
+          return if numeric_to_d.float_type? && specifies_precision?(node, position: 0)
+
+          add_offense(numeric_to_d.source_range) do |corrector|
+            big_decimal_args = node
+                               .arguments
+                               .map(&:source)
+                               .unshift("'#{numeric_to_d.source}'")
+                               .join(', ')
+
+            corrector.replace(node, "BigDecimal(#{big_decimal_args})")
+          end
+        end
 
-        def specifies_precision?(node)
-          node.arguments.size > 1 && !node.arguments[1].hash_type?
+        def specifies_precision?(node, position:)
+          node.arguments.size > position && !node.arguments[position].hash_type?
         end
       end
     end

spec/rubocop/cop/performance/big_decimal_with_numeric_argument_spec.rb

@@ -4,7 +4,18 @@
   it 'registers an offense and corrects when using `BigDecimal` with integer' do
     expect_offense(<<~RUBY)
       BigDecimal(1)
-                 ^ Convert numeric argument to string before passing to `BigDecimal`.
+                 ^ Convert numeric literal to string and pass it to `BigDecimal`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      BigDecimal('1')
+    RUBY
+  end
+
+  it 'registers an offense and corrects when using `Integer#to_d`' do
+    expect_offense(<<~RUBY)
+      1.to_d
+      ^ Convert numeric literal to string and pass it to `BigDecimal`.
     RUBY
 
     expect_correction(<<~RUBY)
@@ -15,7 +26,18 @@
   it 'registers an offense and corrects when using `BigDecimal` with float' do
     expect_offense(<<~RUBY)
       BigDecimal(1.5, exception: true)
-                 ^^^ Convert numeric argument to string before passing to `BigDecimal`.
+                 ^^^ Convert numeric literal to string and pass it to `BigDecimal`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      BigDecimal('1.5', exception: true)
+    RUBY
+  end
+
+  it 'registers an offense and corrects when using `Float#to_d`' do
+    expect_offense(<<~RUBY)
+      1.5.to_d(exception: true)
+      ^^^ Convert numeric literal to string and pass it to `BigDecimal`.
     RUBY
 
     expect_correction(<<~RUBY)
@@ -29,22 +51,47 @@
     RUBY
   end
 
+  it 'does not register an offense when using `Float#to_d` with precision' do
+    expect_no_offenses(<<~RUBY)
+      3.14.to_d(1)
+    RUBY
+  end
+
   it 'does not register an offense when using `BigDecimal` with float and non-literal precision' do
     expect_no_offenses(<<~RUBY)
       precision = 1
       BigDecimal(3.14, precision)
     RUBY
   end
 
+  it 'does not register an offense when using `Float#to_d` with non-literal precision' do
+    expect_no_offenses(<<~RUBY)
+      precision = 1
+      3.14.to_d(precision)
+    RUBY
+  end
+
   it 'does not register an offense when using `BigDecimal` with float, precision, and a keyword argument' do
     expect_no_offenses(<<~RUBY)
       BigDecimal(3.14, 1, exception: true)
     RUBY
   end
 
+  it 'does not register an offense when using `Float#to_d` with precision and a keyword argument' do
+    expect_no_offenses(<<~RUBY)
+      3.14.to_d(1, exception: true)
+    RUBY
+  end
+
   it 'does not register an offense when using `BigDecimal` with string' do
     expect_no_offenses(<<~RUBY)
       BigDecimal('1')
     RUBY
   end
+
+  it 'does not register an offense when using `String#to_d`' do
+    expect_no_offenses(<<~RUBY)
+      '1'.to_d
+    RUBY
+  end
 end