Support signature generation for ActionMailer

ActionMailer automatically generates class methods from the instance methods
user defined via method_missing.  For example, `AccountMailer.welcome_mail`
will be generated from `AccountMail#welcome_mail` that is defined by users.

This starts to support signature generation for auto-generated class methods
for mailer classes dynamically.

Author: tk0miya

README.md

@@ -28,6 +28,7 @@ $ bin/rails g rbs_rails:install
 
 Then, the following three tasks are available.
 
+* `rbs_rails:generate_rbs_for_mailers`: Generate RBS files for Action Mailer classes
 * `rbs_rails:generate_rbs_for_models`: Generate RBS files for Active Record models
 * `rbs_rails:generate_rbs_for_path_helpers`: Generate RBS files for path helpers
 * `rbs_rails:all`: Execute all tasks of RBS Rails
@@ -38,6 +39,9 @@ You can also run rbs_rails from command line:
 # Generate all RBS files
 $ bundle exec rbs_rails all
 
+# Generate RBS files for mailers
+$ bundle exec rbs_rails mailers
+
 # Generate RBS files for models
 $ bundle exec rbs_rails models
 

lib/rbs_rails.rb

@@ -4,6 +4,7 @@
 
 require_relative "rbs_rails/version"
 require_relative "rbs_rails/util"
+require_relative 'rbs_rails/action_mailer'
 require_relative 'rbs_rails/active_record'
 require_relative 'rbs_rails/active_record/enum'
 require_relative 'rbs_rails/path_helpers'

lib/rbs_rails/action_mailer.rb

@@ -0,0 +1,70 @@
+module RbsRails
+  module ActionMailer
+    # @rbs klass: singleton(ActionMailer::Base)
+    def self.class_to_rbs(klass) #: String
+      Generator.new(klass).generate
+    end
+
+    class Generator
+      # @rbs @klass_name: String
+
+      # @rbs klass: singleton(ActionMailer::Base)
+      def initialize(klass) #: void
+        @klass = klass
+        @klass_name = Util.module_name(klass, abs: false)
+      end
+
+      def generate #: String
+        Util.format_rbs klass_decl
+      end
+
+      private def klass_decl #: String
+        <<~RBS
+          # resolve-type-names: false
+
+          #{header}
+          #{methods}
+          #{footer}
+        RBS
+      end
+
+      private def header #: String
+        namespace = +''
+        klass_name(abs: false).split('::').map do |mod_name|
+          namespace += "::#{mod_name}"
+          mod_object = Object.const_get(namespace)
+          case mod_object
+          when Class
+            # @type var superclass: Class
+            superclass = _ = mod_object.superclass
+            superclass_name = Util.module_name(superclass, abs: false)
+
+            "class #{namespace} < ::#{superclass_name}"
+          when Module
+            "module #{namespace}"
+          else
+            raise 'unreachable'
+          end
+        end.join("\n")
+      end
+
+      private def methods #: String
+        klass.action_methods.map do |method_name|
+          "def self.#{method_name}: (*untyped) -> ::ActionMailer::MessageDelivery"
+        end.join("\n")
+      end
+
+      private def footer #: String
+        "end\n" * klass_name(abs: false).split('::').size
+      end
+
+      # @rbs abs: bool
+      private def klass_name(abs: true) #: String
+        abs ? "::#{@klass_name}" : @klass_name
+      end
+
+      private
+      attr_reader :klass #: singleton(ActionMailer::Base)
+    end
+  end
+end

lib/rbs_rails/cli.rb

@@ -28,9 +28,15 @@ def run(argv) #: Integer
         when "all"
           load_application
           load_config
+          generate_mailers
           generate_models
           generate_path_helpers
           0
+        when "mailers"
+          load_application
+          load_config
+          generate_mailers
+          0
         when "models"
           load_application
           load_config
@@ -89,6 +95,18 @@ def install_hooks #: void
       require 'rbs_rails/active_record/enum'
     end
 
+    def generate_mailers #: void
+      Rails.application.eager_load!
+
+      ::ActionMailer::Base.descendants.each do |klass|
+        path = config.signature_root_dir / rbs_path_for(klass)
+        path.dirname.mkpath
+
+        sig = RbsRails::ActionMailer.class_to_rbs(klass)
+        path.write sig
+      end
+    end
+
     def generate_models #: void
       Rails.application.eager_load!
 
@@ -112,17 +130,7 @@ def generate_single_model(klass, dep_builder) #: bool
       return false if config.ignored_model?(klass)
       return false unless RbsRails::ActiveRecord.generatable?(klass)
 
-      original_path, _line = Object.const_source_location(klass.name) rescue nil
-
-      rbs_relative_path = if original_path && Pathname.new(original_path).fnmatch?("#{Rails.root}/**")
-                            Pathname.new(original_path)
-                                    .relative_path_from(Rails.root)
-                                    .sub_ext('.rbs')
-                          else
-                            "app/models/#{klass.name.underscore}.rbs"
-                          end
-
-      path = config.signature_root_dir / rbs_relative_path
+      path = config.signature_root_dir / rbs_path_for(klass)
       path.dirname.mkpath
 
       sig = RbsRails::ActiveRecord.class_to_rbs(klass, dependencies: dep_builder.deps)
@@ -140,6 +148,20 @@ def generate_path_helpers #: void
       path.write sig
     end
 
+    # @rbs klass: singleton(Object)
+    def rbs_path_for(klass) #: String
+      original_path, _line = Object.const_source_location(klass.name) rescue nil
+
+      if original_path && Pathname.new(original_path).fnmatch?("#{Rails.root}/**")
+        Pathname.new(original_path)
+                .relative_path_from(Rails.root)
+                .sub_ext('.rbs')
+                .to_s
+      else
+        "app/models/#{klass.name.underscore}.rbs"
+      end
+    end
+
     def create_option_parser #: OptionParser
       OptionParser.new do |opts|
         opts.banner = <<~BANNER

lib/rbs_rails/rake_task.rb

@@ -23,6 +23,7 @@ def initialize(name = :rbs_rails, &block) #: void
       block.call(self) if block
 
       def_generate_rbs_for_models
+      def_generate_rbs_for_mailers
       def_generate_rbs_for_path_helpers
       def_all
     end
@@ -51,6 +52,17 @@ def def_generate_rbs_for_models #: void
       end
     end
 
+    def def_generate_rbs_for_mailers #: void
+      desc 'Generate RBS files for Action Mailer mailers'
+      task :"#{name}:generate_rbs_for_mailers" do
+        if signature_root_dir
+          sh "rbs_rails", "mailers", "--signature-root-dir=#{signature_root_dir}"
+        else
+          sh "rbs_rails", "mailers"
+        end
+      end
+    end
+
     def def_generate_rbs_for_path_helpers #: void
       desc 'Generate RBS files for path helpers'
       task :"#{name}:generate_rbs_for_path_helpers" do

sig/rbs_rails/action_mailer.rbs

@@ -0,0 +1,32 @@
+# Generated from lib/rbs_rails/action_mailer.rb with RBS::Inline
+
+module RbsRails
+  module ActionMailer
+    # @rbs klass: singleton(ActionMailer::Base)
+    def self.class_to_rbs: (singleton(ActionMailer::Base) klass) -> String
+
+    class Generator
+      @klass_name: String
+
+      # @rbs klass: singleton(ActionMailer::Base)
+      def initialize: (singleton(ActionMailer::Base) klass) -> void
+
+      def generate: () -> String
+
+      private def klass_decl: () -> String
+
+      private def header: () -> String
+
+      private def methods: () -> String
+
+      private def footer: () -> String
+
+      # @rbs abs: bool
+      private def klass_name: (?abs: bool) -> String
+
+      private
+
+      attr_reader klass: singleton(ActionMailer::Base)
+    end
+  end
+end

sig/rbs_rails/cli.rbs

@@ -20,6 +20,8 @@ module RbsRails
 
     def install_hooks: () -> void
 
+    def generate_mailers: () -> void
+
     def generate_models: () -> void
 
     # @rbs klass: singleton(ActiveRecord::Base)
@@ -28,6 +30,9 @@ module RbsRails
 
     def generate_path_helpers: () -> void
 
+    # @rbs klass: singleton(Object)
+    def rbs_path_for: (singleton(Object) klass) -> String
+
     def create_option_parser: () -> OptionParser
   end
 end

sig/rbs_rails/rake_task.rbs

@@ -20,6 +20,8 @@ module RbsRails
 
     def def_generate_rbs_for_models: () -> void
 
+    def def_generate_rbs_for_mailers: () -> void
+
     def def_generate_rbs_for_path_helpers: () -> void
 
     private def signature_root_dir: () -> Pathname?

test/app/app/mailers/application_mailer.rb

@@ -0,0 +1,4 @@
+class ApplicationMailer < ActionMailer::Base
+  default from: '[email protected]'
+  layout 'mailer'
+end

test/app/app/mailers/user_mailer.rb

@@ -0,0 +1,9 @@
+class UserMailer < ApplicationMailer
+  default from: '[email protected]'
+
+  def welcome_email
+    @user = params[:user]
+    @url  = 'http://example.com/login'
+    mail(to: @user.email, subject: 'Welcome to My Awesome Site')
+  end
+end