Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `README.md`:
  Upstream updated copyright year, we don't mention it so kept our version.
- `app/controllers/admin/dashboard_controller.rb`:
  Not really a conflict, upstream change (removing the spam checker) too close
  to glitch-soc changes. Ported upstream changes.
- `app/models/form/admin_settings.rb`:
  Same.
- `app/services/remove_status_service.rb`:
  Same.
- `app/views/admin/settings/edit.html.haml`:
  Same.
- `config/settings.yml`:
  Same.
- `config/environments/production.rb`:
  Not a real conflict, upstream added a default HTTP header, but we have
  extra headers in glitch-soc.
  Added the header.

app/validators/blacklisted_email_validator.rb

@@ -6,26 +6,25 @@ class BlacklistedEmailValidator < ActiveModel::Validator
 
     @email = user.email
 
-    user.errors.add(:email, :blocked) if blocked_email?
+    user.errors.add(:email, :blocked) if blocked_email_provider?
+    user.errors.add(:email, :taken) if blocked_canonical_email?
   end
 
   private
 
-  def blocked_email?
-    on_blacklist? || not_on_whitelist?
+  def blocked_email_provider?
+    disallowed_through_email_domain_block? || disallowed_through_configuration? || not_allowed_through_configuration?
   end
 
-  def on_blacklist?
-    return true  if EmailDomainBlock.block?(@email)
-    return false if Rails.configuration.x.email_domains_blacklist.blank?
-
-    domains = Rails.configuration.x.email_domains_blacklist.gsub('.', '\.')
-    regexp  = Regexp.new("@(.+\\.)?(#{domains})", true)
-
-    regexp.match?(@email)
+  def blocked_canonical_email?
+    CanonicalEmailBlock.block?(@email)
   end
 
-  def not_on_whitelist?
+  def disallowed_through_email_domain_block?
+    EmailDomainBlock.block?(@email)
+  end
+
+  def not_allowed_through_configuration?
     return false if Rails.configuration.x.email_domains_whitelist.blank?
 
     domains = Rails.configuration.x.email_domains_whitelist.gsub('.', '\.')
@@ -33,4 +32,13 @@ class BlacklistedEmailValidator < ActiveModel::Validator
 
     @email !~ regexp
   end
+
+  def disallowed_through_configuration?
+    return false if Rails.configuration.x.email_domains_blacklist.blank?
+
+    domains = Rails.configuration.x.email_domains_blacklist.gsub('.', '\.')
+    regexp  = Regexp.new("@(.+\\.)?(#{domains})", true)
+
+    regexp.match?(@email)
+  end
 end