Add super_diff extension for improved diff output in specs

Gemfile

@@ -21,4 +21,5 @@ end
 group :test do
   gem "debug_inspector"
   gem "dry-types"
+  gem "super_diff"
 end

lib/dry/monads/extensions.rb

@@ -5,3 +5,7 @@
 Dry::Monads.register_extension(:rspec) do
   require "dry/monads/extensions/rspec"
 end
+
+Dry::Monads.register_extension(:super_diff) do
+  require "dry/monads/extensions/super_diff"
+end

lib/dry/monads/extensions/rspec.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "rspec/matchers"
+
 debug_inspector_available =
   begin
     require "debug_inspector"

lib/dry/monads/extensions/super_diff.rb

@@ -0,0 +1,139 @@
+# frozen_string_literal: true
+
+require "super_diff"
+require "super_diff/rspec"
+
+module Dry
+  module Monads
+    module SuperDiff
+      VALUES = [
+        Result::Success,
+        Result::Failure,
+        Maybe::Some,
+        Maybe::None,
+        Try::Value
+      ].freeze
+
+      EXTRACT_VALUE = {
+        Result::Success => lambda(&:value!),
+        Result::Failure => lambda(&:failure),
+        Maybe::Some => lambda(&:value!),
+        Maybe::None => lambda { |_| Unit },
+        Try::Value => lambda(&:value!)
+      }.freeze
+
+      TOKEN_MAP = {
+        Result::Success => "Success(",
+        Result::Failure => "Failure(",
+        Maybe::Some => "Some(",
+        Maybe::None => "None(",
+        Try::Value => "Value("
+      }.freeze
+
+      module OperationTreeFlatteners
+        class MonadicValues < ::SuperDiff::Basic::OperationTreeFlatteners::CustomObject
+          def open_token
+            TOKEN_MAP[operation_tree.underlying_object.class]
+          end
+
+          def close_token = ")"
+
+          def item_prefix_for(_) = ""
+        end
+      end
+
+      module OperationTrees
+        class MonadicValues < ::SuperDiff::Basic::OperationTrees::CustomObject
+          def operation_tree_flattener_class
+            OperationTreeFlatteners::MonadicValues
+          end
+        end
+      end
+
+      module OperationTreeBuilders
+        class MonadicValues < ::SuperDiff::Basic::OperationTreeBuilders::CustomObject
+          def self.applies_to?(expected, actual)
+            VALUES.include?(expected.class) &&
+              actual.instance_of?(expected.class)
+          end
+
+          protected
+
+          def build_operation_tree
+            OperationTrees::MonadicValues.new([], underlying_object: actual)
+          end
+
+          def attribute_names
+            [:value]
+          end
+
+          private
+
+          attr_reader :expected_attributes, :actual_attributes
+
+          def establish_expected_and_actual_attributes
+            @expected_attributes = get_value(expected)
+            @actual_attributes = get_value(actual)
+          end
+
+          def get_value(object)
+            v = EXTRACT_VALUE[object.class].(object)
+
+            if Unit.equal?(v)
+              EMPTY_HASH
+            else
+              {value: v}
+            end
+          end
+        end
+      end
+
+      module Differs
+        class MonadicValues < ::SuperDiff::Basic::Differs::CustomObject
+          def self.applies_to?(expected, actual)
+            VALUES.include?(expected.class) &&
+              expected.instance_of?(actual.class)
+          end
+
+          def operation_tree_builder_class
+            OperationTreeBuilders::MonadicValues
+          end
+        end
+      end
+
+      module InspectionTreeBuilders
+        class MonadicValues < ::SuperDiff::Basic::InspectionTreeBuilders::CustomObject
+          def self.applies_to?(object)
+            VALUES.include?(object.class)
+          end
+
+          def call
+            ::SuperDiff::Core::InspectionTree.new do |t1|
+              t1.as_lines_when_rendering_to_lines(
+                collection_bookend: :open
+              ) do |t2|
+                t2.add_text(TOKEN_MAP[object.class])
+
+                v = EXTRACT_VALUE[object.class].(object)
+
+                unless Unit.equal?(v)
+                  t2.nested do |t3|
+                    t3.add_inspection_of v
+                  end
+                end
+                t2.add_text(")")
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end
+
+SuperDiff.configuration.tap do |config|
+  config.prepend_extra_differ_classes(Dry::Monads::SuperDiff::Differs::MonadicValues)
+  config.prepend_extra_inspection_tree_builder_classes(
+    Dry::Monads::SuperDiff::InspectionTreeBuilders::MonadicValues
+  )
+end