users: add stricter username rules.

Add stricter username rules:

* Only allow usernames to contain basic letters, numbers, CJK characters, underscores, dashes and periods.
* Don't allow names to start or end with punctuation.
* Don't allow names to have multiple underscores in a row.
* Don't allow active users to have names that look like deleted users (e.g. "user_1234").
* Don't allow emoji or any other Unicode characters except for Chinese, Japanese, and Korean
  characters. CJK characters are currently grandfathered in but will be disallowed in the future.

Users with an invalid name will be shown a permanent sitewide banner until they change their name.

test/unit/user_test.rb

@@ -148,27 +148,51 @@ class UserTest < ActiveSupport::TestCase
     context "name" do
       should "not contain whitespace" do
         # U+2007: https://en.wikipedia.org/wiki/Figure_space
-        user = FactoryBot.build(:user, :name => "foo\u2007bar")
+        user = build(:user, name: "foo\u2007bar")
         user.save
-        assert_equal(["Name cannot have whitespace or colons"], user.errors.full_messages)
+        assert_equal(["Name can't contain whitespace"], user.errors.full_messages)
+      end
+
+      should "be less than 25 characters long" do
+        user = build(:user, name: "a"*25)
+        user.save
+        assert_equal(["Name must be less than 25 characters long"], user.errors.full_messages)
       end
 
       should "not contain a colon" do
-        user = FactoryBot.build(:user, :name => "a:b")
+        user = build(:user, name: "a:b")
         user.save
-        assert_equal(["Name cannot have whitespace or colons"], user.errors.full_messages)
+        assert_equal(["Name can't contain ':'"], user.errors.full_messages)
       end
 
       should "not begin with an underscore" do
-        user = FactoryBot.build(:user, :name => "_x")
+        user = build(:user, name: "_x")
         user.save
-        assert_equal(["Name cannot begin or end with an underscore"], user.errors.full_messages)
+        assert_equal(["Name can't start with '_'"], user.errors.full_messages)
       end
 
       should "not end with an underscore" do
-        user = FactoryBot.build(:user, :name => "x_")
+        user = build(:user, name: "x_")
         user.save
-        assert_equal(["Name cannot begin or end with an underscore"], user.errors.full_messages)
+        assert_equal(["Name can't end with '_'"], user.errors.full_messages)
+      end
+
+      should "not contain consecutive underscores" do
+        user = build(:user, name: "x__y")
+        user.save
+        assert_equal(["Name can't contain multiple underscores in a row"], user.errors.full_messages)
+      end
+
+      should "not allow non-ASCII characters" do
+        user = build(:user, name: "Pokémon")
+        user.save
+        assert_equal(["Name must contain only basic letters or numbers"], user.errors.full_messages)
+      end
+
+      should "not be in the same format as a deleted user" do
+        user = build(:user, name: "user_1234")
+        user.save
+        assert_equal(["Name can't be the same as a deleted user"], user.errors.full_messages)
       end
 
       should "not allow blacklisted names" do
@@ -177,11 +201,6 @@ class UserTest < ActiveSupport::TestCase
         user.save
         assert_equal(["Name is not allowed"], user.errors.full_messages)
       end
-
-      should "be updated" do
-        @user = FactoryBot.create(:user)
-        @user.update_attribute(:name, "danzig")
-      end
     end
 
     context "searching for users by name" do
@@ -206,10 +225,14 @@ class UserTest < ActiveSupport::TestCase
         assert_nil(User.name_to_id("does_not_exist"))
       end
 
-      should "work for names containing asterisks or backlashes" do
-        @user1 = create(:user, name: "user*1")
-        @user2 = create(:user, name: "user*2")
-        @user3 = create(:user, name: "user\*3")
+      should "work for names containing asterisks or backslashes" do
+        @user1 = build(:user, name: "user*1")
+        @user2 = build(:user, name: "user*2")
+        @user3 = build(:user, name: "user\*3")
+
+        @user1.save(validate: false)
+        @user2.save(validate: false)
+        @user3.save(validate: false)
 
         assert_equal(@user1.id, User.find_by_name("user*1").id)
         assert_equal(@user2.id, User.find_by_name("user*2").id)
@@ -259,9 +282,13 @@ class UserTest < ActiveSupport::TestCase
 
     context "when searched by name" do
       should "match wildcards" do
-        user1 = FactoryBot.create(:user, :name => "foo")
-        user2 = FactoryBot.create(:user, :name => "foo*bar")
-        user3 = FactoryBot.create(:user, :name => "bar\*baz")
+        user1 = build(:user, name: "foo")
+        user2 = build(:user, name: "foo*bar")
+        user3 = build(:user, name: "bar\*baz")
+
+        user1.save(validate: false)
+        user2.save(validate: false)
+        user3.save(validate: false)
 
         assert_equal([user2.id, user1.id], User.search(name: "foo*").map(&:id))
         assert_equal([user2.id], User.search(name: "foo\*bar").map(&:id))