Update Style/NilLambda to handle procs as well

changelog/change_update_stylenillambda_to_handle_procs_as.md

@@ -0,0 +1 @@
+* [#9776](https://github.com/rubocop/rubocop/pull/9776): Update `Style/NilLambda` to handle procs as well. ([@dvandersluis][])

lib/rubocop/cop/style/nil_lambda.rb

@@ -3,8 +3,8 @@
 module RuboCop
   module Cop
     module Style
-      # This cop checks for lambdas that always return nil, which can be replaced
-      # with an empty lambda instead.
+      # This cop checks for lambdas and procs that always return nil,
+      # which can be replaced with an empty lambda or proc instead.
       #
       # @example
       #   # bad
@@ -14,6 +14,12 @@ module Style
       #     next nil
       #   end
       #
+      #   proc { nil }
+      #
+      #   Proc.new do
+      #     break nil
+      #   end
+      #
       #   # good
       #   -> {}
       #
@@ -22,31 +28,42 @@ module Style
       #
       #   -> (x) { nil if x }
       #
+      #   proc {}
+      #
+      #   Proc.new { nil if x }
+      #
       class NilLambda < Base
         extend AutoCorrector
         include RangeHelp
 
-        MSG = 'Use an empty lambda instead of always returning nil.'
+        MSG = 'Use an empty %<type>s instead of always returning nil.'
 
         # @!method nil_return?(node)
         def_node_matcher :nil_return?, <<~PATTERN
           { ({return next break} nil) (nil) }
         PATTERN
 
         def on_block(node)
-          return unless node.lambda?
+          return unless node.lambda? || node.proc?
           return unless nil_return?(node.body)
 
-          add_offense(node) do |corrector|
-            range = if node.single_line?
-                      range_with_surrounding_space(range: node.body.loc.expression)
-                    else
-                      range_by_whole_lines(node.body.loc.expression, include_final_newline: true)
-                    end
-
-            corrector.remove(range)
+          message = format(MSG, type: node.lambda? ? 'lambda' : 'proc')
+          add_offense(node, message: message) do |corrector|
+            autocorrect(corrector, node)
           end
         end
+
+        private
+
+        def autocorrect(corrector, node)
+          range = if node.single_line?
+                    range_with_surrounding_space(range: node.body.loc.expression)
+                  else
+                    range_by_whole_lines(node.body.loc.expression, include_final_newline: true)
+                  end
+
+          corrector.remove(range)
+        end
       end
     end
   end

spec/rubocop/cop/style/nil_lambda_spec.rb

@@ -171,4 +171,202 @@
       RUBY
     end
   end
+
+  context 'proc' do
+    it 'registers an offense when returning nil implicitly' do
+      expect_offense(<<~RUBY)
+        proc do
+        ^^^^^^^ Use an empty proc instead of always returning nil.
+          nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        proc do
+        end
+      RUBY
+    end
+
+    it 'registers an offense when returning nil with `return`' do
+      expect_offense(<<~RUBY)
+        proc do
+        ^^^^^^^ Use an empty proc instead of always returning nil.
+          return nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        proc do
+        end
+      RUBY
+    end
+
+    it 'registers an offense when returning nil with `break`' do
+      expect_offense(<<~RUBY)
+        proc do
+        ^^^^^^^ Use an empty proc instead of always returning nil.
+          break nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        proc do
+        end
+      RUBY
+    end
+
+    it 'registers an offense when returning nil with `next`' do
+      expect_offense(<<~RUBY)
+        proc do
+        ^^^^^^^ Use an empty proc instead of always returning nil.
+          next nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        proc do
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when not returning nil' do
+      expect_no_offenses(<<~RUBY)
+        proc do
+          6
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when doing more than returning nil' do
+      expect_no_offenses(<<~RUBY)
+        proc do |x|
+          x ? x.method : nil
+        end
+      RUBY
+    end
+
+    it 'does not remove block params or change spacing' do
+      expect_offense(<<~RUBY)
+        fn = proc do |x|
+             ^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+               nil
+             end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        fn = proc do |x|
+             end
+      RUBY
+    end
+
+    it 'properly corrects single line' do
+      expect_offense(<<~RUBY)
+        proc { nil }
+        ^^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        proc {}
+      RUBY
+    end
+  end
+
+  context 'Proc.new' do
+    it 'registers an offense when returning nil implicitly' do
+      expect_offense(<<~RUBY)
+        Proc.new do
+        ^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+          nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Proc.new do
+        end
+      RUBY
+    end
+
+    it 'registers an offense when returning nil with `return`' do
+      expect_offense(<<~RUBY)
+        Proc.new do
+        ^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+          return nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Proc.new do
+        end
+      RUBY
+    end
+
+    it 'registers an offense when returning nil with `break`' do
+      expect_offense(<<~RUBY)
+        Proc.new do
+        ^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+          break nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Proc.new do
+        end
+      RUBY
+    end
+
+    it 'registers an offense when returning nil with `next`' do
+      expect_offense(<<~RUBY)
+        Proc.new do
+        ^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+          next nil
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Proc.new do
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when not returning nil' do
+      expect_no_offenses(<<~RUBY)
+        Proc.new do
+          6
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when doing more than returning nil' do
+      expect_no_offenses(<<~RUBY)
+        Proc.new do |x|
+          x ? x.method : nil
+        end
+      RUBY
+    end
+
+    it 'does not remove block params or change spacing' do
+      expect_offense(<<~RUBY)
+        fn = Proc.new do |x|
+             ^^^^^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+               nil
+             end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        fn = Proc.new do |x|
+             end
+      RUBY
+    end
+
+    it 'properly corrects single line' do
+      expect_offense(<<~RUBY)
+        Proc.new { nil }
+        ^^^^^^^^^^^^^^^^ Use an empty proc instead of always returning nil.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Proc.new {}
+      RUBY
+    end
+  end
 end