[Fix #12988] Add new Style/AmbiguousEndlessMethodDefinition cop.

Author: dvandersluis

changelog/new_add_new_style_endless_method_operator_precedence.md

@@ -0,0 +1 @@
+* [#12988](https://github.com/rubocop/rubocop/issues/12988): Add new `Style/AmbiguousEndlessMethodDefinition` cop. ([@dvandersluis][])

config/default.yml

@@ -3143,6 +3143,11 @@ Style/Alias:
     - prefer_alias
     - prefer_alias_method
 
+Style/AmbiguousEndlessMethodDefinition:
+  Description: 'Checks for endless methods inside operators of lower precedence.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Style/AndOr:
   Description: 'Use &&/|| instead of and/or.'
   StyleGuide: '#no-and-or-or'

lib/rubocop.rb

@@ -90,6 +90,7 @@
 require_relative 'rubocop/cop/mixin/empty_lines_around_body' # relies on range
 require_relative 'rubocop/cop/mixin/empty_parameter'
 require_relative 'rubocop/cop/mixin/end_keyword_alignment'
+require_relative 'rubocop/cop/mixin/endless_method_rewriter'
 require_relative 'rubocop/cop/mixin/enforce_superclass'
 require_relative 'rubocop/cop/mixin/first_element_line_break'
 require_relative 'rubocop/cop/mixin/frozen_string_literal'
@@ -460,6 +461,7 @@
 require_relative 'rubocop/cop/style/access_modifier_declarations'
 require_relative 'rubocop/cop/style/accessor_grouping'
 require_relative 'rubocop/cop/style/alias'
+require_relative 'rubocop/cop/style/ambiguous_endless_method_definition'
 require_relative 'rubocop/cop/style/and_or'
 require_relative 'rubocop/cop/style/arguments_forwarding'
 require_relative 'rubocop/cop/style/array_coercion'

lib/rubocop/cop/mixin/endless_method_rewriter.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # Common functionality for rewriting endless methods to normal method definitions
+    module EndlessMethodRewriter
+      def correct_to_multiline(corrector, node)
+        replacement = <<~RUBY.strip
+          def #{node.method_name}#{arguments(node)}
+            #{node.body.source}
+          end
+        RUBY
+
+        corrector.replace(node, replacement)
+      end
+
+      private
+
+      def arguments(node, missing = '')
+        node.arguments.any? ? node.arguments.source : missing
+      end
+    end
+  end
+end

lib/rubocop/cop/style/ambiguous_endless_method_definition.rb

@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # Looks for endless methods inside operations of lower precedence (`and`, `or`, and
+      # modifier forms of `if`, `unless`, `while`, `until`) that are ambiguous due to
+      # lack of parentheses. This may lead to unexpected behavior as the code may appear
+      # to use these keywords as part of the method but in fact they modify
+      # the method definition itself.
+      #
+      # In these cases, using a normal method definition is more clear.
+      #
+      # @example
+      #
+      #   # bad
+      #   def foo = true if bar
+      #
+      #   # good - using a non-endless method is more explicit
+      #   def foo
+      #     true
+      #   end if bar
+      #
+      #   # ok - method body is explicit
+      #   def foo = (true if bar)
+      #
+      #   # ok - method definition is explicit
+      #   (def foo = true) if bar
+      class AmbiguousEndlessMethodDefinition < Base
+        extend TargetRubyVersion
+        extend AutoCorrector
+        include EndlessMethodRewriter
+        include RangeHelp
+
+        minimum_target_ruby_version 3.0
+
+        MSG = 'Avoid using `%<keyword>s` statements with endless methods.'
+
+        # @!method ambiguous_endless_method_body(node)
+        def_node_matcher :ambiguous_endless_method_body, <<~PATTERN
+          ^${
+            (if _ <def _>)
+            ({and or} def _)
+            ({while until} _ def)
+          }
+        PATTERN
+
+        def on_def(node)
+          return unless node.endless?
+
+          operation = ambiguous_endless_method_body(node)
+          return unless operation
+
+          return unless modifier_form?(operation)
+
+          add_offense(operation, message: format(MSG, keyword: keyword(operation))) do |corrector|
+            correct_to_multiline(corrector, node)
+          end
+        end
+
+        private
+
+        def modifier_form?(operation)
+          return true if operation.and_type? || operation.or_type?
+
+          operation.modifier_form?
+        end
+
+        def keyword(operation)
+          if operation.respond_to?(:keyword)
+            operation.keyword
+          else
+            operation.operator
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/style/endless_method.rb

@@ -48,6 +48,7 @@ module Style
       #
       class EndlessMethod < Base
         include ConfigurableEnforcedStyle
+        include EndlessMethodRewriter
         extend TargetRubyVersion
         extend AutoCorrector
 
@@ -81,20 +82,6 @@ def handle_disallow_style(node)
 
           add_offense(node) { |corrector| correct_to_multiline(corrector, node) }
         end
-
-        def correct_to_multiline(corrector, node)
-          replacement = <<~RUBY.strip
-            def #{node.method_name}#{arguments(node)}
-              #{node.body.source}
-            end
-          RUBY
-
-          corrector.replace(node, replacement)
-        end
-
-        def arguments(node, missing = '')
-          node.arguments.any? ? node.arguments.source : missing
-        end
       end
     end
   end

spec/rubocop/cop/style/ambiguous_endless_method_definition_spec.rb

@@ -0,0 +1,70 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Style::AmbiguousEndlessMethodDefinition, :config do
+  context 'Ruby >= 3.0', :ruby30 do
+    it 'does not register an offense for a non endless method' do
+      expect_no_offenses(<<~RUBY)
+        def foo
+        end
+      RUBY
+    end
+
+    %i[and or if unless while until].each do |operator|
+      context "with #{operator}" do
+        it "does not register an offense for a non endless method followed by `#{operator}`" do
+          expect_no_offenses(<<~RUBY)
+            def foo
+            end #{operator} bar
+          RUBY
+        end
+
+        it 'does not register an offense when the operator is already wrapped in parens' do
+          expect_no_offenses(<<~RUBY)
+            def foo = (true #{operator} bar)
+          RUBY
+        end
+
+        it 'does not register an offense when the method definition is already wrapped in parens' do
+          expect_no_offenses(<<~RUBY)
+            (def foo = true) #{operator} bar
+          RUBY
+        end
+
+        unless %i[and or].include?(operator)
+          it "does not register an offense for non-modifier `#{operator}`" do
+            expect_no_offenses(<<~RUBY)
+              #{operator} bar
+                def foo = true
+              end
+            RUBY
+          end
+        end
+
+        it "registers and offense and corrects an endless method followed by `#{operator}`" do
+          expect_offense(<<~RUBY, operator: operator)
+            def foo = true #{operator} bar
+            ^^^^^^^^^^^^^^^^{operator}^^^^ Avoid using `#{operator}` statements with endless methods.
+          RUBY
+
+          expect_correction(<<~RUBY)
+            def foo
+              true
+            end #{operator} bar
+          RUBY
+        end
+      end
+    end
+
+    it 'does not register an offense for `&&`' do
+      expect_no_offenses(<<~RUBY)
+        def foo = true && bar
+      RUBY
+    end
+
+    it 'does not register an offense for `||`' do
+      expect_no_offenses(<<~RUBY)
+        def foo = true || bar
+      RUBY
+    end
+  end
+end