Prism: Adds support for mailer subjects (#666)

Author: davidwessman

lib/i18n/tasks/scanners/prism_scanners/nodes.rb

@@ -224,8 +224,14 @@ def add_child(node)
     end
 
     def process # rubocop:disable Metrics/AbcSize,Metrics/CyclomaticComplexity,Metrics/MethodLength,Metrics/PerceivedComplexity
-      return super unless controller?
+      if controller?
+        process_controller
+      else
+        super
+      end
+    end
 
+    def process_controller
       methods_by_name = @methods.group_by(&:name)
       private_methods_by_name = @private_methods.group_by(&:name)
 
@@ -283,15 +289,19 @@ def private_methods!
     end
 
     def support_relative_keys?
-      @rails && controller?
+      controller? || mailer?
     end
 
     def path
       (@parent&.path || []) + [path_name]
     end
 
     def controller?
-      @node.name.to_s.end_with?("Controller")
+      @rails && @node.name.to_s.end_with?("Controller")
+    end
+
+    def mailer?
+      @rails && @node.name.to_s.end_with?("Mailer")
     end
 
     def path_name

lib/i18n/tasks/scanners/prism_scanners/visitor.rb

@@ -163,15 +163,69 @@ def handle_comments(node)
     # ---- Rails specific methods ----
     # Returns true if the node was handled
     def handle_rails_call_node(node, &)
+      # First, handle calls that should be matched everywhere
       case node.name
-      when :before_action
-        rails_handle_before_action(node, &)
       when :human_attribute_name
         rails_handle_human_attribute_name(node)
+        return true
       when :human
-        return if node.receiver.name != :model_name
-
+        return false if node.receiver.nil? || node.receiver.name != :model_name
         rails_handle_model_name(node)
+        return true
+      end
+
+      if @current_class&.controller?
+        rails_handle_controller_call_node(node, &)
+      elsif @current_class&.mailer?
+        rails_handle_mailer_call_node(node, &)
+      else
+        false
+      end
+    end
+
+    def rails_handle_controller_call_node(node, &)
+      case node.name
+      when :before_action
+        rails_handle_before_action(node, &)
+        true
+      else
+        false
+      end
+    end
+
+    def rails_handle_mailer_call_node(node, &)
+      case node.name
+      when :mail
+        _array_args, keywords = process_arguments(node)
+        if keywords.key?("subject")
+          # Let traversal continue so nested calls (e.g., t('.subject') or default_i18n_subject)
+          # get processed by their own handlers.
+          false
+        else
+          parent.add_translation_call(
+            TranslationCall.new(
+              node: node,
+              receiver: nil,
+              key: ".subject",
+              parent: parent,
+              options: {}
+            )
+          )
+          true
+        end
+      when :default_i18n_subject
+        parent.add_translation_call(
+          TranslationCall.new(
+            node: node,
+            receiver: nil,
+            key: ".subject",
+            parent: parent,
+            options: {}
+          )
+        )
+        true
+      else
+        false
       end
     end
 

spec/prism_scanner_spec.rb

@@ -439,6 +439,40 @@ def value
     end
   end
 
+  describe "mailers" do
+    it "detects mailer" do
+      source = <<~RUBY
+        class UserMailer < ApplicationMailer
+          def welcome_email(user)
+            @user = user
+            # Make sure it does not expect `.subject` from this method
+            mail(to: @user.email, subject: t('.subject_with_other_key'))
+          end
+
+          def notification_email(user)
+            @user = user
+            mail(to: @user.email, subject: default_i18n_subject)
+          end
+
+          def other_email(user)
+            mail(to: user.email)
+          end
+        end
+      RUBY
+
+      occurrences =
+        process_string("app/mailers/user_mailer.rb", source)
+
+      expect(occurrences.map(&:first).uniq).to match_array(
+        %w[
+          user_mailer.notification_email.subject
+          user_mailer.other_email.subject
+          user_mailer.welcome_email.subject_with_other_key
+        ]
+      )
+    end
+  end
+
   describe "magic comments" do
     it "i18n-tasks-use" do
       source = <<~'RUBY'