FIX: Don't error out on empty reserved_usernames setting (#29305)

We're seeing errors in logs due to some sites setting the reserved_usernames setting to nil. This is causing multiple use cases upstream of User#reserved_username? to error out.

This commit changes from using the raw #reserved_usernames to using the #reserved_usernames_map helper which exists on list-type site settings. It returns an empty array if the raw value is nil or empty string.

app/models/user.rb

@@ -440,11 +440,9 @@ class User < ActiveRecord::Base
 
     return true if SiteSetting.here_mention == username
 
-    SiteSetting
-      .reserved_usernames
-      .unicode_normalize
-      .split("|")
-      .any? { |reserved| username.match?(/\A#{Regexp.escape(reserved).gsub('\*', ".*")}\z/) }
+    SiteSetting.reserved_usernames_map.any? do |reserved|
+      username.match?(/\A#{Regexp.escape(reserved.unicode_normalize).gsub('\*', ".*")}\z/)
+    end
   end
 
   def self.editable_user_custom_fields(by_staff: false)

config/site_settings.yml

@@ -652,6 +652,7 @@ users:
     type: list
     list_type: compact
     default: "admin|moderator|administrator|mod|sys|system|community|info|you|name|username|user|nickname|discourse|discourseorg|discourseforum|support|all|here"
+    mandatory_values: "admin|moderator|administrator|mod|sys|system|community|info|you|name|username|user|nickname|discourse|discourseorg|discourseforum|support|all|here"
   min_password_length:
     client: true
     default: 10

spec/lib/user_name_suggester_spec.rb

@@ -10,6 +10,8 @@ RSpec.describe UserNameSuggester do
       SiteSetting.reserved_usernames = ""
     end
 
+    let(:fallback_username) { I18n.t("fallback_username") + "1" }
+
     it "keeps adding numbers to the username" do
       Fabricate(:user, username: "sam")
       Fabricate(:user, username: "sAm1")
@@ -20,7 +22,7 @@ RSpec.describe UserNameSuggester do
     end
 
     it "doesn't raise an error on nil username and suggest the fallback username" do
-      expect(UserNameSuggester.suggest(nil)).to eq(I18n.t("fallback_username"))
+      expect(UserNameSuggester.suggest(nil)).to eq(fallback_username)
     end
 
     it "doesn't raise an error on integer username" do
@@ -86,7 +88,7 @@ RSpec.describe UserNameSuggester do
 
     it "suggest a fallback username if name contains only invalid characters" do
       suggestion = UserNameSuggester.suggest("---")
-      expect(suggestion).to eq(I18n.t("fallback_username"))
+      expect(suggestion).to eq(fallback_username)
     end
 
     it "allows dots in the middle" do
@@ -164,7 +166,6 @@ RSpec.describe UserNameSuggester do
       end
 
       it "uses fallback username if there are Unicode characters only" do
-        fallback_username = I18n.t("fallback_username")
         expect(UserNameSuggester.suggest("طائر")).to eq(fallback_username)
         expect(UserNameSuggester.suggest("πουλί")).to eq(fallback_username)
       end
@@ -218,7 +219,7 @@ RSpec.describe UserNameSuggester do
       it "uses allowlist" do
         SiteSetting.allowed_unicode_username_characters = "[äöüßÄÖÜẞ]"
 
-        expect(UserNameSuggester.suggest("πουλί")).to eq(I18n.t("fallback_username"))
+        expect(UserNameSuggester.suggest("πουλί")).to eq(fallback_username)
         expect(UserNameSuggester.suggest("a鳥b")).to eq("a_b")
         expect(UserNameSuggester.suggest("Löwe")).to eq("Löwe")
 

spec/models/discourse_connect_spec.rb

@@ -12,6 +12,8 @@ RSpec.describe DiscourseConnect do
     Jobs.run_immediately!
   end
 
+  let(:fallback_username) { I18n.t("fallback_username") + "1" }
+
   def make_sso
     sso = DiscourseConnectBase.new
     sso.sso_url = "http://meta.discorse.org/topics/111"
@@ -576,7 +578,7 @@ RSpec.describe DiscourseConnect do
     sso.email = "mail@mail.com"
 
     user = sso.lookup_or_create_user(ip_address)
-    expect(user.username).to eq "user"
+    expect(user.username).to eq(fallback_username)
   end
 
   it "doesn't use email as a source for username suggestions by default" do
@@ -589,7 +591,7 @@ RSpec.describe DiscourseConnect do
     sso.email = "mail@mail.com"
 
     user = sso.lookup_or_create_user(ip_address)
-    expect(user.username).to eq I18n.t("fallback_username")
+    expect(user.username).to eq(fallback_username)
   end
 
   it "uses email as a source for username suggestions if enabled" do

spec/models/user_spec.rb

@@ -1076,6 +1076,12 @@ RSpec.describe User do
       expect(User.reserved_username?("löwe")).to eq(true) # NFC
       expect(User.reserved_username?("käfer")).to eq(true) # NFC
     end
+
+    it "does not error out when there are no reserved usernames" do
+      SiteSetting.stubs(:reserved_usernames).returns(nil)
+
+      expect { User.username_available?("Foo") }.not_to raise_error
+    end
   end
 
   describe "email_validator" do