Follow review feedback:

* Just use ClassMethods
* Ignore the value if variable_environment_scope is not available
* Use a partial

app/models/ee/ci/variable.rb

@@ -3,15 +3,13 @@ module EE
     module Variable
       extend ActiveSupport::Concern
 
-      module VariableClassMethods
+      module ClassMethods
         def key_uniqueness_scope
           %i[project_id environment_scope]
         end
       end
 
       prepended do
-        singleton_class.prepend(VariableClassMethods)
-
         validates(
           :environment_scope,
           presence: true,
@@ -19,15 +17,16 @@ module EE
                     message: ::Gitlab::Regex.environment_scope_regex_message }
         )
 
-        validate :validate_updating_environment_scope
+        before_save :verify_updating_environment_scope
 
         private
 
-        def validate_updating_environment_scope
+        def verify_updating_environment_scope
           return unless environment_scope_changed?
 
           unless project.feature_available?(:variable_environment_scope)
-            errors.add(:environment_scope, 'is not enabled for this project')
+            # Ignore the changes to this value to mimic CE behaviour
+            self.environment_scope = environment_scope_was
           end
         end
       end

app/views/projects/variables/_form.html.haml

@@ -7,14 +7,7 @@
   .form-group
     = f.label :value, "Value", class: "label-light"
     = f.text_area :value, class: "form-control", placeholder: "PROJECT_VARIABLE"
-  - if @project.feature_available?(:variable_environment_scope)
-    .form-group
-      = f.label :environment_scope, "Environment scope", class: "label-light"
-      = f.text_field :environment_scope, class: "form-control", placeholder: "*"
-      .help-block
-        This variable will be passed only to jobs with a matching environment name.
-        <code>*</code> is a wildcard that matches all environments (existing or not).
-        = link_to icon('question-circle'), help_page_path('ci/variables/README', anchor: 'limiting-environment-scopes-of-secret-variables'), target: '_blank'
+  = render 'projects/variables/ee/environment_scope', f: f
   .form-group
     .checkbox
       = f.label :protected do

app/views/projects/variables/ee/_environment_scope.html.haml

+- if @project.feature_available?(:variable_environment_scope)
+  .form-group
+    = f.label :environment_scope, "Environment scope", class: "label-light"
+    = f.text_field :environment_scope, class: "form-control", placeholder: "*"
+    .help-block
+      This variable will be passed only to jobs with a matching environment name.
+      <code>*</code> is a wildcard that matches all environments (existing or not).
+      = link_to icon('question-circle'), help_page_path('ci/variables/README', anchor: 'limiting-environment-scopes-of-secret-variables'), target: '_blank'

spec/models/ci/build_spec.rb

@@ -1422,7 +1422,7 @@ describe Ci::Build, :models do
                 .merge(project: project, environment_scope: 'stag*'))
 
           # Skip this validation so that we could test for existing data
-          allow(variable).to receive(:validate_updating_environment_scope)
+          allow(variable).to receive(:verify_updating_environment_scope)
             .and_return(true)
 
           variable.save!

spec/models/ci/variable_spec.rb

@@ -20,6 +20,11 @@ describe Ci::Variable, models: true do
     it { is_expected.to allow_value('*').for(:environment_scope) }
     it { is_expected.to allow_value('review/*').for(:environment_scope) }
     it { is_expected.not_to allow_value('').for(:environment_scope) }
+
+    it do
+      is_expected.to validate_uniqueness_of(:key)
+        .scoped_to(:project_id, :environment_scope)
+    end
   end
 
   # EE
@@ -29,15 +34,14 @@ describe Ci::Variable, models: true do
     end
 
     it { is_expected.to allow_value('*').for(:environment_scope) }
-    it { is_expected.not_to allow_value('review/*').for(:environment_scope) }
-  end
 
-  let(:key_scope) do
-    [:project_id, :environment_scope] # EE
+    it 'ignores the changes to environment_scope' do
+      expect do
+        subject.update!(environment_scope: 'review/*')
+      end.not_to change { subject.environment_scope }
+    end
   end
 
-  it { is_expected.to validate_uniqueness_of(:key).scoped_to(key_scope) }
-
   describe '.unprotected' do
     subject { described_class.unprotected }
 

spec/models/project_spec.rb

@@ -2296,7 +2296,7 @@ describe Project, models: true do
       before do
         # Skip this validation so that we could test for existing data
         allow_any_instance_of(Ci::Variable)
-          .to receive(:validate_updating_environment_scope).and_return(true)
+          .to receive(:verify_updating_environment_scope).and_return(true)
       end
 
       shared_examples 'matching environment scope' do