Entity name setter method

Gemfile

@@ -32,4 +32,6 @@ group :test do
   gem "minitest-reporters", "~> 1.4"
 
   gem "simplecov", require: false
+
+  gem "grape-entity", require: false
 end

Gemfile.lock

@@ -53,6 +53,9 @@ GEM
       mustermann-grape (~> 1.1.0)
       rack (>= 2)
       zeitwerk
+    grape-entity (1.0.1)
+      activesupport (>= 3.0.0)
+      multi_json (>= 1.3.2)
     i18n (1.14.5)
       concurrent-ruby (~> 1.0)
     io-console (0.7.2)
@@ -67,6 +70,7 @@ GEM
       builder
       minitest (>= 5.0)
       ruby-progressbar
+    multi_json (1.15.0)
     mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
     mustermann-grape (1.1.0)
@@ -169,6 +173,7 @@ PLATFORMS
 
 DEPENDENCIES
   bundler-audit
+  grape-entity
   grape_sorbet!
   irb
   minitest (~> 5.0)

lib/grape_sorbet.rb

@@ -5,3 +5,4 @@ module GrapeSorbet
 end
 
 require_relative "grape_sorbet/version"
+require_relative "grape_sorbet/grape_entity_name"

lib/grape_sorbet/grape_entity_name.rb

@@ -0,0 +1,89 @@
+# typed: strict
+# frozen_string_literal: true
+
+require "sorbet-runtime"
+
+module GrapeSorbet
+  # This is a patch for Grape::Entity to make it easier to define custom entity names when using Sorbet.
+  #
+  # This patch defines a class setter `entity_name=` that can be used to define a custom entity name in a single line,
+  # while still working as expected with grape-swagger:
+  # ```
+  # class Link < Grape::Entity
+  #   self.entity_name = "LinkedStatus"
+  # end
+  # ```
+  #
+  # Without this patch, you would have to define a custom entity name like this:
+  # ```
+  # class Link < Grape::Entity
+  #   extend T::Sig
+  #
+  #   sig { returns(String) }
+  #   def self.entity_name
+  #     "LinkedStatus"
+  #   end
+  # end
+  # ```
+  #
+  # or even more verbose, if you're using the `Style/ClassMethodsDefinitions` Rubocop rule with
+  # `EnforcedStyle: self_class`:
+  # ```
+  # class Link < Grape::Entity
+  #   class << self
+  #     extend T::Sig
+  #
+  #     sig { returns(String) }
+  #     def entity_name
+  #       "LinkedStatus"
+  #     end
+  #   end
+  # end
+  # ```
+  module GrapeEntityName
+    extend T::Sig
+
+    include Kernel
+
+    # Sets the entity name.
+    #
+    # Used by grape-swagger to define a custom name to use in the OpenAPI schema instead of generating it from the
+    # fully qualified class name.
+    #
+    # @param entity_name [String] The custom entity name.
+    sig { params(entity_name: String).returns(String) }
+    attr_writer :entity_name
+
+    # Returns the custom entity name if one has been set (using `entity_name=`), otherwise raises an error.
+    #
+    # @return [String] The custom entity name.
+    # @raise [StandardError] If no custom entity name has been set.
+    sig { returns(String) }
+    def entity_name
+      @entity_name = T.let(@entity_name, T.nilable(String))
+
+      return @entity_name unless @entity_name.nil?
+
+      raise "entity_name has not been set for #{self}, call `#{self}.entity_name = \"...\"` to set it"
+    end
+
+    sig { params(method_name: T.any(String, Symbol), include_all: T.untyped).returns(T::Boolean) }
+    def respond_to?(method_name, include_all = false)
+      # grape-swagger checks if the model class responds to `:entity_name`, so we need to return false if
+      # `@entity_name` is nil (meaning `entity_name=` was never called).
+      if method_name.to_sym == :entity_name
+        return !!(defined?(@entity_name) && !@entity_name.nil?)
+      end
+
+      super
+    end
+  end
+end
+
+begin
+  require "grape-entity"
+rescue LoadError
+  return
+else
+  Grape::Entity.extend(GrapeSorbet::GrapeEntityName)
+end