Scan assert_equal methods and rectify any offenses with a custom Ru…

…bocop cop (#7130)

Merge pull request 7130

rubocop/jekyll/assert_equal_literal_actual.rb

@@ -0,0 +1,149 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Jekyll
+      # Checks for `assert_equal(exp, act, msg = nil)` calls containing literal values as
+      # second argument. The second argument should ideally be a method called on the tested
+      # instance.
+      #
+      # @example
+      #   # bad
+      #   assert_equal @foo.bar, "foobar"
+      #   assert_equal @alpha.beta, { "foo" => "bar", "lorem" => "ipsum" }
+      #   assert_equal @alpha.omega, ["foobar", "lipsum"]
+      #
+      #   # good
+      #   assert_equal "foobar", @foo.bar
+      #
+      #   assert_equal(
+      #     { "foo" => "bar", "lorem" => "ipsum" },
+      #     @alpha.beta
+      #   )
+      #
+      #   assert_equal(
+      #     ["foobar", "lipsum"],
+      #     @alpha.omega
+      #   )
+      #
+      class AssertEqualLiteralActual < Cop
+        MSG = "Provide the 'expected value' as the first argument to `assert_equal`.".freeze
+
+        SIMPLE_LITERALS = %i(
+          true
+          false
+          nil
+          int
+          float
+          str
+          sym
+          complex
+          rational
+          regopt
+        ).freeze
+
+        COMPLEX_LITERALS = %i(
+          array
+          hash
+          pair
+          irange
+          erange
+          regexp
+        ).freeze
+
+        def_node_matcher :literal_actual?, <<-PATTERN
+          (send nil? :assert_equal $(send ...) $#literal?)
+        PATTERN
+
+        def_node_matcher :literal_actual_with_msg?, <<-PATTERN
+          (send nil? :assert_equal $(send ...) $#literal? $#opt_msg?)
+        PATTERN
+
+        def on_send(node)
+          return unless literal_actual?(node) || literal_actual_with_msg?(node)
+          add_offense(node, location: :expression)
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            corrector.replace(node.loc.expression, replacement(node))
+          end
+        end
+
+        private
+
+        def opt_msg?(node)
+          node&.source
+        end
+
+        # This is not implement using a NodePattern because it seems
+        # to not be able to match against an explicit (nil) sexp
+        def literal?(node)
+          node && (simple_literal?(node) || complex_literal?(node))
+        end
+
+        def simple_literal?(node)
+          SIMPLE_LITERALS.include?(node.type)
+        end
+
+        def complex_literal?(node)
+          COMPLEX_LITERALS.include?(node.type) &&
+            node.each_child_node.all?(&method(:literal?))
+        end
+
+        def replacement(node)
+          _, _, first_param, second_param, optional_param = *node
+
+          replaced_text = \
+            if second_param.type == :hash
+              replace_hash_with_variable(first_param.source, second_param.source)
+            elsif second_param.type == :array && second_param.source != "[]"
+              replace_array_with_variable(first_param.source, second_param.source)
+            else
+              replace_based_on_line_length(first_param.source, second_param.source)
+            end
+
+          return "#{replaced_text}, #{optional_param.source}" if optional_param
+          replaced_text
+        end
+
+        def replace_based_on_line_length(first_expression, second_expression)
+          result = "assert_equal #{second_expression}, #{first_expression}"
+          return result if result.length < 80
+
+          # fold long lines independent of Rubocop configuration for better readability
+          <<~TEXT
+            assert_equal(
+              #{second_expression},
+              #{first_expression}
+            )
+          TEXT
+        end
+
+        def replace_hash_with_variable(first_expression, second_expression)
+          expect_expression = if second_expression.start_with?("{")
+                                second_expression
+                              else
+                                "{#{second_expression}}"
+                              end
+          <<~TEXT
+            expected = #{expect_expression}
+            assert_equal expected, #{first_expression}
+          TEXT
+        end
+
+        def replace_array_with_variable(first_expression, second_expression)
+          expect_expression = if second_expression.start_with?("%")
+                                second_expression
+                              else
+                                Array(second_expression)
+                              end
+          <<~TEXT
+            expected = #{expect_expression}
+            assert_equal expected, #{first_expression}
+          TEXT
+        end
+      end
+    end
+  end
+end