Don't try to resize non-variable avatars

app/controllers/users/avatars_controller.rb

@@ -10,7 +10,7 @@ class Users::AvatarsController < ApplicationController
     if @user.system?
       redirect_to view_context.image_path("system_user.png")
     elsif @user.avatar.attached?
-      redirect_to rails_blob_url(@user.avatar.variant(:thumb), disposition: "inline")
+      redirect_to rails_blob_url(@user.avatar_thumbnail, disposition: "inline")
     elsif stale? @user, cache_control: cache_control
       render_initials
     end

app/models/user.rb

@@ -1,12 +1,8 @@
 class User < ApplicationRecord
-  include Accessor, Assignee, Attachable, Configurable, EmailAddressChangeable,
+  include Accessor, Assignee, Attachable, Avatar, Configurable, EmailAddressChangeable,
     Mentionable, Named, Notifiable, Role, Searcher, Watcher
   include Timelined # Depends on Accessor
 
-  has_one_attached :avatar do |attachable|
-    attachable.variant :thumb, resize_to_fill: [ 256, 256 ]
-  end
-
   belongs_to :account
   belongs_to :identity, optional: true
 

app/models/user/avatar.rb

@@ -0,0 +1,13 @@
+module User::Avatar
+  extend ActiveSupport::Concern
+
+  included do
+    has_one_attached :avatar do |attachable|
+      attachable.variant :thumb, resize_to_fill: [ 256, 256 ]
+    end
+  end
+
+  def avatar_thumbnail
+    avatar.variable? ? avatar.variant(:thumb) : avatar
+  end
+end

test/controllers/users/avatars_controller_test.rb

@@ -32,7 +32,7 @@ class Users::AvatarsControllerTest < ActionDispatch::IntegrationTest
 
     get user_avatar_path(users(:david))
 
-    assert_redirected_to rails_blob_url(users(:david).avatar.variant(:thumb), disposition: "inline")
+    assert_redirected_to rails_blob_url(users(:david).avatar_thumbnail, disposition: "inline")
   end
 
   test "show other image redirects to the blob url" do
@@ -41,7 +41,7 @@ class Users::AvatarsControllerTest < ActionDispatch::IntegrationTest
 
     get user_avatar_path(users(:kevin))
 
-    assert_redirected_to rails_blob_url(users(:kevin).avatar.variant(:thumb), disposition: "inline")
+    assert_redirected_to rails_blob_url(users(:kevin).avatar_thumbnail, disposition: "inline")
   end
 
   test "delete self" do

test/fixtures/files/avatar.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
+  <circle cx="50" cy="50" r="40" fill="#4a90d9"/>
+</svg>

test/models/user/avatar_test.rb

@@ -0,0 +1,17 @@
+require "test_helper"
+
+class User::AvatarTest < ActiveSupport::TestCase
+  test "avatar_thumbnail returns variant for variable images" do
+    users(:david).avatar.attach(io: File.open(file_fixture("moon.jpg")), filename: "moon.jpg", content_type: "image/jpeg")
+
+    assert users(:david).avatar.variable?
+    assert_equal users(:david).avatar.variant(:thumb).blob, users(:david).avatar_thumbnail.blob
+  end
+
+  test "avatar_thumbnail returns original blob for non-variable images" do
+    users(:david).avatar.attach(io: File.open(file_fixture("avatar.svg")), filename: "avatar.svg", content_type: "image/svg+xml")
+
+    assert_not users(:david).avatar.variable?
+    assert_equal users(:david).avatar.blob, users(:david).avatar_thumbnail.blob
+  end
+end