Add error message when user tries to follow their own account (#31910)

app/controllers/api/v1/accounts_controller.rb

@@ -16,6 +16,7 @@ class Api::V1::AccountsController < Api::BaseController
   before_action :check_account_confirmation, except: [:index, :create]
   before_action :check_enabled_registrations, only: [:create]
   before_action :check_accounts_limit, only: [:index]
+  before_action :check_following_self, only: [:follow]
 
   skip_before_action :require_authenticated_user!, only: :create
 
@@ -101,6 +102,10 @@ class Api::V1::AccountsController < Api::BaseController
     raise(Mastodon::ValidationError) if account_ids.size > DEFAULT_ACCOUNTS_LIMIT
   end
 
+  def check_following_self
+    render json: { error: I18n.t('accounts.self_follow_error') }, status: 403 if current_user.account.id == @account.id
+  end
+
   def relationships(**options)
     AccountRelationshipsPresenter.new([@account], current_user.account_id, **options)
   end

config/locales/en.yml

@@ -21,6 +21,7 @@ en:
       one: Post
       other: Posts
     posts_tab_heading: Posts
+    self_follow_error: Following your own account is not allowed
   admin:
     account_actions:
       action: Perform action

spec/requests/api/v1/accounts_spec.rb

@@ -163,6 +163,26 @@ RSpec.describe '/api/v1/accounts' do
       end
     end
 
+    context 'when user tries to follow their own account' do
+      subject do
+        post "/api/v1/accounts/#{other_account.id}/follow", headers: headers
+      end
+
+      let(:locked) { false }
+      let(:other_account) { user.account }
+
+      it 'returns http forbidden and error message' do
+        subject
+
+        error_msg = I18n.t('accounts.self_follow_error')
+
+        expect(response).to have_http_status(403)
+        expect(response.parsed_body[:error]).to eq(error_msg)
+      end
+
+      it_behaves_like 'forbidden for wrong scope', 'read:accounts'
+    end
+
     context 'when modifying follow options' do
       let(:locked) { false }