UX: Add validator for `SiteSetting#sso_overrides_email`.

config/locales/server.en.yml

@@ -1580,6 +1580,8 @@ en:
       email_polling_disabled: "You must enable either manual or POP3 polling before enabling reply by email."
       user_locale_not_enabled: "You must first enable 'allow user locale' before enabling this setting."
       invalid_regex: "Regex is invalid or not allowed."
+      email_editable_enabled: "You must disable 'email editable' before enabling this setting."
+      enable_sso_disabled: "You must first enable 'enable sso' before enabling this setting."
 
   search:
     within_post: "#%{post_number} by %{username}"

config/site_settings.yml

@@ -304,7 +304,9 @@ login:
     regex: '^https?:\/\/.+[^\/]$'
   sso_secret: ''
   sso_overrides_bio: false
-  sso_overrides_email: false
+  sso_overrides_email:
+    default: false
+    validator: "SsoOverridesEmailValidator"
   sso_overrides_username: false
   sso_overrides_name: false
   sso_overrides_avatar:

lib/validators/sso_overrides_email_validator.rb

@@ -0,0 +1,20 @@
+class SsoOverridesEmailValidator
+  def initialize(opts={})
+    @opts = opts
+  end
+
+  def valid_value?(val)
+    return true if val == 'f'
+    return false if !SiteSetting.enable_sso?
+    return false if SiteSetting.email_editable?
+    true
+  end
+
+  def error_message
+    if !SiteSetting.enable_sso?
+      I18n.t('site_settings.errors.enable_sso_disabled')
+    elsif SiteSetting.email_editable?
+      I18n.t('site_settings.errors.email_editable_enabled')
+    end
+  end
+end

spec/components/validators/sso_overrides_email_validator_spec.rb

@@ -0,0 +1,71 @@
+require 'rails_helper'
+
+RSpec.describe SsoOverridesEmailValidator do
+  subject { described_class.new }
+
+  describe '#valid_value?' do
+    describe "when 'email editable' is true" do
+      before do
+        SiteSetting.enable_sso = true
+        SiteSetting.email_editable = true
+      end
+
+      describe 'when val is false' do
+        it 'should be valid' do
+          expect(subject.valid_value?('f')).to eq(true)
+        end
+      end
+
+      describe 'when value is true' do
+        it 'should not be valid' do
+          expect(subject.valid_value?('t')).to eq(false)
+
+          expect(subject.error_message).to eq(I18n.t(
+            'site_settings.errors.email_editable_enabled'
+          ))
+        end
+      end
+    end
+
+    describe "when 'email editable' is false" do
+      before do
+        SiteSetting.enable_sso = true
+        SiteSetting.email_editable = false
+      end
+
+      describe 'when value is false' do
+        it 'should be valid' do
+          expect(subject.valid_value?('f')).to eq(true)
+        end
+      end
+
+      describe 'when value is true' do
+        it 'should be valid' do
+          expect(subject.valid_value?('t')).to eq(true)
+        end
+      end
+    end
+
+    describe "when 'enable sso' is false" do
+      before do
+        SiteSetting.enable_sso = false
+      end
+
+      describe 'when value is false' do
+        it 'should be valid' do
+          expect(subject.valid_value?('f')).to eq(true)
+        end
+      end
+
+      describe 'when value is true' do
+        it 'should not be valid' do
+          expect(subject.valid_value?('t')).to eq(false)
+
+          expect(subject.error_message).to eq(I18n.t(
+            'site_settings.errors.enable_sso_disabled'
+          ))
+        end
+      end
+    end
+  end
+end