Simplify #file_method? implementation

It turns out that some methods are available in more than one Gem, so I
tried to group things to make it simpler and easier to maintain.
I also removed the support for multiple file uploads, because those are
very application-specific, it didn't seem worth the cost of the
complexity/maintainence.

lib/simple_form/form_builder.rb

@@ -572,34 +572,28 @@ def find_custom_type(attribute_name)
       }.try(:last) if SimpleForm.input_mappings
     end
 
+    # Internal: Try to discover whether an attribute corresponds to a file.
+    #
+    # Most upload Gems add some kind of attributes to the ActiveRecord's model they are included in.
+    # This method tries to guess if an attribute belongs to some of these Gems by checking the presence
+    # of their methods using `#respond_to?`.
+    #
+    # Note: this does not support multiple file upload inputs, as this is very application-specific.
+    #
+    # The order here was choosen based on the popularity of the Gems and for commodity - e.g. the method
+    # with the suffix `_url` is present in three Gems, so it's checked with priority:
+    #
+    # - `#{attribute_name}_attachment` - ActiveStorage >= `5.2` and Refile >= `0.2.0` <= `0.4.0`
+    # - `#{attribute_name}_url` - Shrine >= `0.9.0`, Refile >= `0.6.0` and CarrierWave >= `0.2.1`
+    # - `#{attribute_name}_attacher` - Refile >= `0.4.0` and Shrine >= `0.9.0`
+    # - `#{attribute_name}_file_name` - Paperclip ~> `2.0` (added for backwards compatibility)
+    #
+    # Returns a Boolean.
     def file_method?(attribute_name)
-      activestorage?(attribute_name) || shrine?(attribute_name) ||
-        carrierwave?(attribute_name) || paperclip?(attribute_name) ||
-        refile?(attribute_name)
-    end
-
-    def activestorage?(attribute_name)
-      @object.class.try(:reflect_on_attachment, attribute_name).present? ||
-        @object.class.try(:reflect_on_association, "#{attribute_name}_attachment").present? ||
-        @object.class.try(:reflect_on_association, "#{attribute_name}_attachments").present?
-    end
-
-    def shrine?(attribute_name)
-      @object.respond_to?("#{attribute_name}_attacher")
-    end
-
-    def carrierwave?(attribute_name)
-      @object.respond_to?("#{attribute_name}_url") ||
-        @object.respond_to?("#{attribute_name}_urls")
-    end
-
-    def paperclip?(attribute_name)
-      @object.respond_to?("#{attribute_name}_file_name")
-    end
-
-    def refile?(attribute_name)
       @object.respond_to?("#{attribute_name}_attachment") ||
-        @object.respond_to?("#{attribute_name}_attachment_definition")
+        @object.respond_to?("#{attribute_name}_url") ||
+        @object.respond_to?("#{attribute_name}_attacher") ||
+        @object.respond_to?("#{attribute_name}_file_name")
     end
 
     def find_attribute_column(attribute_name)

test/form_builder/general_test.rb

@@ -239,49 +239,24 @@ def with_custom_form_for(object, *args, &block)
     assert_select 'form select#user_updated_at_1i.datetime'
   end
 
-  test 'builder generates file input for activestorage' do
+  test 'builder generates file input for ActiveStorage >= 5.2 and Refile >= 0.2.0 <= 0.4.0' do
     with_form_for UserWithAttachment.build, :avatar
     assert_select 'form input#user_with_attachment_avatar.file'
   end
 
-  test 'builder generates file input for activestorage in Rails 5.2' do
-    with_form_for UserWithAttachment.build, :image
-    assert_select 'form input#user_with_attachment_image.file'
-  end
-
-  test 'builder generates file input for activestorage in Rails 5.2 with multiple files' do
-    with_form_for UserWithAttachment.build, :images
-    assert_select 'form input#user_with_attachment_images.file'
-  end
-
-  test 'builder generates file input for carrierwave' do
-    with_form_for UserWithAttachment.build, :photo
-    assert_select 'form input#user_with_attachment_photo.file'
-  end
-
-  test 'builder generates file input for carrierwave with multiple files' do
-    with_form_for UserWithAttachment.build, :photos
-    assert_select 'form input#user_with_attachment_photos.file'
-  end
-
-  test 'builder generates file input for paperclip' do
-    with_form_for UserWithAttachment.build, :portrait
-    assert_select 'form input#user_with_attachment_portrait.file'
+  test 'builder generates file input for Shrine >= 0.9.0, Refile >= 0.6.0 and CarrierWave >= 0.2.1' do
+    with_form_for UserWithAttachment.build, :cover
+    assert_select 'form input#user_with_attachment_cover.file'
   end
 
-  test 'builder generates file input for refile' do
+  test 'builder generates file input for Refile >= 0.4.0 and Shrine >= 0.9.0' do
     with_form_for UserWithAttachment.build, :profile_image
     assert_select 'form input#user_with_attachment_profile_image.file'
   end
 
-  test 'builder generates file input for refile with multiple files' do
-    with_form_for UserWithAttachment.build, :profile_images_files
-    assert_select 'form input#user_with_attachment_profile_images_files.file'
-  end
-
-  test 'builder generates file input for shrine' do
-    with_form_for UserWithAttachment.build, :cover
-    assert_select 'form input#user_with_attachment_cover.file'
+  test 'builder generates file input for Paperclip ~> 2.0' do
+    with_form_for UserWithAttachment.build, :portrait
+    assert_select 'form input#user_with_attachment_portrait.file'
   end
 
   test 'build generates select if a collection is given' do

test/support/models.rb

@@ -335,35 +335,19 @@ class UserNumber1And2 < User
 end
 
 class UserWithAttachment < User
-  def self.reflect_on_attachment(attachment)
-    OpenStruct.new if attachment == :avatar
-  end
-
-  def self.reflect_on_association(association)
-    OpenStruct.new if ["image_attachment", "images_attachments"].include?(association)
+  def avatar_attachment
+    OpenStruct.new
   end
 
-  def photo_url
-    "/photos/1.png"
+  def cover_url
+    "/uploads/cover.png"
   end
 
-  def photos_urls
-    ["/photos/1.png", "/photos/2.png"]
+  def profile_image_attacher
+    OpenStruct.new
   end
 
   def portrait_file_name
     "portrait.png"
   end
-
-  def profile_image_attachment
-    OpenStruct.new
-  end
-
-  def profile_images_files_attachment_definition
-    OpenStruct.new
-  end
-
-  def cover_url
-    "/uploads/cover.png"
-  end
 end