gitlab-org--gitlab-foss/doc/development/ee_features.md

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Guidelines for implementing Enterprise Edition features

• Write the code and the tests.: As with any code, EE features should have good test coverage to prevent regressions.
• Write documentation.: Add documentation to the doc/ directory. Describe the feature and include screenshots, if applicable. Indicate what editions the feature applies to.
• Submit a MR to the www-gitlab-com project.: Add the new feature to the EE features list.

Act as CE when unlicensed

Since the implementation of GitLab CE features to work with unlicensed EE instance GitLab Enterprise Edition should work like GitLab Community Edition when no license is active. So EE features always should be guarded by project.feature_available? or group.feature_available? (or License.feature_available? if it is a system-wide feature).

CE specs should remain untouched as much as possible and extra specs should be added for EE. Licensed features can be stubbed using the spec helper stub_licensed_features in EE::LicenseHelpers.

You can force GitLab to act as CE by either deleting the ee/ directory or by setting the FOSS_ONLY environment variable to something that evaluates as true. The same works for running tests (for example FOSS_ONLY=1 yarn jest).

CI pipelines in a FOSS context

By default, merge request pipelines for development run in an EE-context only. If you are developing features that differ between FOSS and EE, you may wish to run pipelines in a FOSS context as well.

To run pipelines in both contexts, include RUN AS-IF-FOSS in the merge request title.

See the As-if-FOSS jobs pipelines documentation for more information.

Separation of EE code

All EE code should be put inside the ee/ top-level directory. The rest of the code should be as close to the CE files as possible.

EE-only features

If the feature being developed is not present in any form in CE, we don't need to put the code under the EE namespace. For example, an EE model could go into: ee/app/models/awesome.rb using Awesome as the class name. This is applied not only to models. Here's a list of other examples:

• ee/app/controllers/foos_controller.rb
• ee/app/finders/foos_finder.rb
• ee/app/helpers/foos_helper.rb
• ee/app/mailers/foos_mailer.rb
• ee/app/models/foo.rb
• ee/app/policies/foo_policy.rb
• ee/app/serializers/foo_entity.rb
• ee/app/serializers/foo_serializer.rb
• ee/app/services/foo/create_service.rb
• ee/app/validators/foo_attr_validator.rb
• ee/app/workers/foo_worker.rb
• ee/app/views/foo.html.haml
• ee/app/views/foo/_bar.html.haml

This works because for every path that is present in CE's eager-load/auto-load paths, we add the same ee/-prepended path in config/application.rb. This also applies to views.

Testing EE-only features

To test an EE class that doesn't exist in CE, create the spec file as you normally would in the ee/spec directory, but without the second ee/ subdirectory. For example, a class ee/app/models/vulnerability.rb would have its tests in ee/spec/models/vulnerability_spec.rb.

EE features based on CE features

For features that build on existing CE features, write a module in the EE namespace and inject it in the CE class, on the last line of the file that the class resides in. This makes conflicts less likely to happen during CE to EE merges because only one line is added to the CE class - the line that injects the module. For example, to prepend a module into the User class you would use the following approach:

class User < ActiveRecord::Base
  # ... lots of code here ...
end

User.prepend_if_ee('EE::User')

Do not use methods such as prepend, extend, and include. Instead, use prepend_if_ee, extend_if_ee, or include_if_ee. These methods take a String containing the full module name as the argument, not the module itself.

Since the module would require an EE namespace, the file should also be put in an ee/ sub-directory. For example, we want to extend the user model in EE, so we have a module called ::EE::User put inside ee/app/models/ee/user.rb.

This is also not just applied to models. Here's a list of other examples:

• ee/app/controllers/ee/foos_controller.rb
• ee/app/finders/ee/foos_finder.rb
• ee/app/helpers/ee/foos_helper.rb
• ee/app/mailers/ee/foos_mailer.rb
• ee/app/models/ee/foo.rb
• ee/app/policies/ee/foo_policy.rb
• ee/app/serializers/ee/foo_entity.rb
• ee/app/serializers/ee/foo_serializer.rb
• ee/app/services/ee/foo/create_service.rb
• ee/app/validators/ee/foo_attr_validator.rb
• ee/app/workers/ee/foo_worker.rb

Testing EE features based on CE features

To test an EE namespaced module that extends a CE class with EE features, create the spec file as you normally would in the ee/spec directory, including the second ee/ subdirectory. For example, an extension ee/app/models/ee/user.rb would have its tests in ee/app/models/ee/user_spec.rb.

In the RSpec.describe call, use the CE class name where the EE module would be used. For example, in ee/app/models/ee/user_spec.rb, the test would start with:

RSpec.describe User do
  describe 'ee feature added through extension'
end

Overriding CE methods

To override a method present in the CE codebase, use prepend. It lets you override a method in a class with a method from a module, while still having access the class's implementation with super.

There are a few gotchas with it:

• you should always extend ::Gitlab::Utils::Override and use override to guard the "overrider" method to ensure that if the method gets renamed in CE, the EE override won't be silently forgotten.

• when the "overrider" would add a line in the middle of the CE implementation, you should refactor the CE method and split it in smaller methods. Or create a "hook" method that is empty in CE, and with the EE-specific implementation in EE.

• when the original implementation contains a guard clause (e.g. return unless condition), we cannot easily extend the behavior by overriding the method, because we can't know when the overridden method (i.e. calling super in the overriding method) would want to stop early. In this case, we shouldn't just override it, but update the original method to make it call the other method we want to extend, like a template method pattern. For example, given this base:

    class Base
      def execute
        return unless enabled?
  
        # ...
        # ...
      end
    end
  

  Instead of just overriding Base#execute, we should update it and extract the behavior into another method:

    class Base
      def execute
        return unless enabled?
  
        do_something
      end
  
      private
  
      def do_something
        # ...
        # ...
      end
    end
  

  Then we're free to override that do_something without worrying about the guards:

    module EE::Base
      extend ::Gitlab::Utils::Override
  
      override :do_something
      def do_something
        # Follow the above pattern to call super and extend it
      end
    end
  

When prepending, place them in the ee/ specific sub-directory, and wrap class or module in module EE to avoid naming conflicts.

For example to override the CE implementation of ApplicationController#after_sign_out_path_for:

def after_sign_out_path_for(resource)
  current_application_settings.after_sign_out_path.presence || new_user_session_path
end

Instead of modifying the method in place, you should add prepend to the existing file:

class ApplicationController < ActionController::Base
  # ...

  def after_sign_out_path_for(resource)
    current_application_settings.after_sign_out_path.presence || new_user_session_path
  end

  # ...
end

ApplicationController.prepend_if_ee('EE::ApplicationController')

And create a new file in the ee/ sub-directory with the altered implementation:

module EE
  module ApplicationController
    extend ::Gitlab::Utils::Override

    override :after_sign_out_path_for
    def after_sign_out_path_for(resource)
      if Gitlab::Geo.secondary?
        Gitlab::Geo.primary_node.oauth_logout_url(@geo_logout_state)
      else
        super
      end
    end
  end
end

Overriding CE class methods

The same applies to class methods, except we want to use ActiveSupport::Concern and put extend ::Gitlab::Utils::Override within the block of class_methods. Here's an example:

module EE
  module Groups
    module GroupMembersController
      extend ActiveSupport::Concern

      class_methods do
        extend ::Gitlab::Utils::Override

        override :admin_not_required_endpoints
        def admin_not_required_endpoints
          super.concat(%i[update override])
        end
      end
    end
  end
end

Use self-descriptive wrapper methods

When it's not possible/logical to modify the implementation of a method, then wrap it in a self-descriptive method and use that method.

For example, in GitLab-FOSS, the only user created by the system is User.ghost but in EE there are several types of bot-users that aren't really users. It would be incorrect to override the implementation of User#ghost?, so instead we add a method #internal? to app/models/user.rb. The implementation will be:

def internal?
  ghost?
end

In EE, the implementation ee/app/models/ee/users.rb would be:

override :internal?
def internal?
  super || bot?
end

Code in config/routes

When we add draw :admin in config/routes.rb, the application will try to load the file located in config/routes/admin.rb, and also try to load the file located in ee/config/routes/admin.rb.

In EE, it should at least load one file, at most two files. If it cannot find any files, an error will be raised. In CE, since we don't know if there will be an EE route, it will not raise any errors even if it cannot find anything.

This means if we want to extend a particular CE route file, just add the same file located in ee/config/routes. If we want to add an EE only route, we could still put draw :ee_only in both CE and EE, and add ee/config/routes/ee_only.rb in EE, similar to render_if_exists.

Code in app/controllers/

In controllers, the most common type of conflict is with before_action that has a list of actions in CE but EE adds some actions to that list.

The same problem often occurs for params.require / params.permit calls.

Mitigations

Separate CE and EE actions/keywords. For instance for params.require in ProjectsController:

def project_params
  params.require(:project).permit(project_params_attributes)
end

# Always returns an array of symbols, created however best fits the use case.
# It _should_ be sorted alphabetically.
def project_params_attributes
  %i[
    description
    name
    path
  ]
end

In the EE::ProjectsController module:

def project_params_attributes
  super + project_params_attributes_ee
end

def project_params_attributes_ee
  %i[
    approvals_before_merge
    approver_group_ids
    approver_ids
    ...
  ]
end

Code in app/models/

EE-specific models should extend EE::Model.

For example, if EE has a specific Tanuki model, you would place it in ee/app/models/ee/tanuki.rb.

Code in app/views/

It's a very frequent problem that EE is adding some specific view code in a CE view. For instance the approval code in the project's settings page.

Mitigations

Blocks of code that are EE-specific should be moved to partials. This avoids conflicts with big chunks of HAML code that are not fun to resolve when you add the indentation to the equation.

EE-specific views should be placed in ee/app/views/, using extra sub-directories if appropriate.

Code in lib/gitlab/background_migration/

When you create EE-only background migrations, you have to plan for users that downgrade GitLab EE to CE. In other words, every EE-only migration has to be present in CE code but with no implementation, instead you need to extend it on EE side.

GitLab CE:

# lib/gitlab/background_migration/prune_orphaned_geo_events.rb

module Gitlab
  module BackgroundMigration
    class PruneOrphanedGeoEvents
      def perform(table_name)
      end
    end
  end
end

Gitlab::BackgroundMigration::PruneOrphanedGeoEvents.prepend_if_ee('EE::Gitlab::BackgroundMigration::PruneOrphanedGeoEvents')

GitLab EE:

# ee/lib/ee/gitlab/background_migration/prune_orphaned_geo_events.rb

module EE
  module Gitlab
    module BackgroundMigration
      module PruneOrphanedGeoEvents
        extend ::Gitlab::Utils::Override

        override :perform
        def perform(table_name = EVENT_TABLES.first)
          return if ::Gitlab::Database.read_only?

          deleted_rows = prune_orphaned_rows(table_name)
          table_name   = next_table(table_name) if deleted_rows.zero?

          ::BackgroundMigrationWorker.perform_in(RESCHEDULE_DELAY, self.class.name.demodulize, table_name) if table_name
        end
      end
    end
  end
end

Code in app/graphql/

EE-specific mutations, resolvers, and types should be added to ee/app/graphql/{mutations,resolvers,types}.

To override a CE mutation, resolver, or type, create the file in ee/app/graphql/ee/{mutations,resolvers,types} and add new code to a prepended block.

For example, if CE has a mutation called Mutations::Tanukis::Create and you wanted to add a new argument, place the EE override in ee/app/graphql/ee/mutations/tanukis/create.rb:

module EE
  module Mutations
    module Tanukis
      module Create
        extend ActiveSupport::Concern

        prepended do
          argument :name,
                   GraphQL::STRING_TYPE,
                   required: false,
                   description: 'Tanuki name'
        end
      end
    end
  end
end

Using render_if_exists

Instead of using regular render, we should use render_if_exists, which will not render anything if it cannot find the specific partial. We use this so that we could put render_if_exists in CE, keeping code the same between CE and EE.

The advantages of this:

• Very clear hints about where we're extending EE views while reading CE code.

The disadvantage of this:

• If we have typos in the partial name, it would be silently ignored.

Caveats

The render_if_exists view path argument must be relative to app/views/ and ee/app/views. Resolving an EE template path that is relative to the CE view path will not work.

- # app/views/projects/index.html.haml

= render_if_exists 'button' # Will not render `ee/app/views/projects/_button` and will quietly fail
= render_if_exists 'projects/button' # Will render `ee/app/views/projects/_button`

Using render_ce

For render and render_if_exists, they search for the EE partial first, and then CE partial. They would only render a particular partial, not all partials with the same name. We could take the advantage of this, so that the same partial path (e.g. shared/issuable/form/default_templates) could be referring to the CE partial in CE (i.e. app/views/shared/issuable/form/_default_templates.html.haml), while EE partial in EE (i.e. ee/app/views/shared/issuable/form/_default_templates.html.haml). This way, we could show different things between CE and EE.

However sometimes we would also want to reuse the CE partial in EE partial because we might just want to add something to the existing CE partial. We could workaround this by adding another partial with a different name, but it would be tedious to do so.

In this case, we could as well just use render_ce which would ignore any EE partials. One example would be ee/app/views/shared/issuable/form/_default_templates.html.haml:

- if @project.feature_available?(:issuable_default_templates)
  = render_ce 'shared/issuable/form/default_templates'
- elsif show_promotions?
  = render 'shared/promotions/promote_issue_templates'

In the above example, we can't use render 'shared/issuable/form/default_templates' because it would find the same EE partial, causing infinite recursion. Instead, we could use render_ce so it ignores any partials in ee/ and then it would render the CE partial (i.e. app/views/shared/issuable/form/_default_templates.html.haml) for the same path (i.e. shared/issuable/form/default_templates). This way we could easily wrap around the CE partial.

Code in lib/

Place EE-specific logic in the top-level EE module namespace. Namespace the class beneath the EE module just as you would normally.

For example, if CE has LDAP classes in lib/gitlab/ldap/ then you would place EE-specific LDAP classes in ee/lib/ee/gitlab/ldap.

Code in lib/api/

It can be very tricky to extend EE features by a single line of prepend_if_ee, and for each different Grape feature, we might need different strategies to extend it. To apply different strategies easily, we would use extend ActiveSupport::Concern in the EE module.

Put the EE module files following EE features based on CE features.

EE API routes

For EE API routes, we put them in a prepended block:

module EE
  module API
    module MergeRequests
      extend ActiveSupport::Concern

      prepended do
        params do
          requires :id, type: String, desc: 'The ID of a project'
        end
        resource :projects, requirements: ::API::API::NAMESPACE_OR_PROJECT_REQUIREMENTS do
          # ...
        end
      end
    end
  end
end

Note that due to namespace differences, we need to use the full qualifier for some constants.

EE parameters

We can define params and utilize use in another params definition to include parameters defined in EE. However, we need to define the "interface" first in CE in order for EE to override it. We don't have to do this in other places due to prepend_if_ee, but Grape is complex internally and we couldn't easily do that, so we'll follow regular object-oriented practices that we define the interface first here.

For example, suppose we have a few more optional parameters for EE. We can move the parameters out of the Grape::API::Instance class to a helper module, so we can inject it before it would be used in the class.

module API
  class Projects < Grape::API::Instance
    helpers Helpers::ProjectsHelpers
  end
end

Given this CE API params:

module API
  module Helpers
    module ProjectsHelpers
      extend ActiveSupport::Concern
      extend Grape::API::Helpers

      params :optional_project_params_ce do
        # CE specific params go here...
      end

      params :optional_project_params_ee do
      end

      params :optional_project_params do
        use :optional_project_params_ce
        use :optional_project_params_ee
      end
    end
  end
end

API::Helpers::ProjectsHelpers.prepend_if_ee('EE::API::Helpers::ProjectsHelpers')

We could override it in EE module:

module EE
  module API
    module Helpers
      module ProjectsHelpers
        extend ActiveSupport::Concern

        prepended do
          params :optional_project_params_ee do
            # EE specific params go here...
          end
        end
      end
    end
  end
end

EE helpers

To make it easy for an EE module to override the CE helpers, we need to define those helpers we want to extend first. Try to do that immediately after the class definition to make it easy and clear:

module API
  class JobArtifacts < Grape::API::Instance
    # EE::API::JobArtifacts would override the following helpers
    helpers do
      def authorize_download_artifacts!
        authorize_read_builds!
      end
    end
  end
end

API::JobArtifacts.prepend_if_ee('EE::API::JobArtifacts')

And then we can follow regular object-oriented practices to override it:

module EE
  module API
    module JobArtifacts
      extend ActiveSupport::Concern

      prepended do
        helpers do
          def authorize_download_artifacts!
            super
            check_cross_project_pipelines_feature!
          end
        end
      end
    end
  end
end

EE-specific behavior

Sometimes we need EE-specific behavior in some of the APIs. Normally we could use EE methods to override CE methods, however API routes are not methods and therefore can't be simply overridden. We need to extract them into a standalone method, or introduce some "hooks" where we could inject behavior in the CE route. Something like this:

module API
  class MergeRequests < Grape::API::Instance
    helpers do
      # EE::API::MergeRequests would override the following helpers
      def update_merge_request_ee(merge_request)
      end
    end

    put ':id/merge_requests/:merge_request_iid/merge' do
      merge_request = find_project_merge_request(params[:merge_request_iid])

      # ...

      update_merge_request_ee(merge_request)

      # ...
    end
  end
end

API::MergeRequests.prepend_if_ee('EE::API::MergeRequests')

Note that update_merge_request_ee doesn't do anything in CE, but then we could override it in EE:

module EE
  module API
    module MergeRequests
      extend ActiveSupport::Concern

      prepended do
        helpers do
          def update_merge_request_ee(merge_request)
            # ...
          end
        end
      end
    end
  end
end

EE route_setting

It's very hard to extend this in an EE module, and this is simply storing some meta-data for a particular route. Given that, we could simply leave the EE route_setting in CE as it won't hurt and we are just not going to use those meta-data in CE.

We could revisit this policy when we're using route_setting more and whether or not we really need to extend it from EE. For now we're not using it much.

Utilizing class methods for setting up EE-specific data

Sometimes we need to use different arguments for a particular API route, and we can't easily extend it with an EE module because Grape has different context in different blocks. In order to overcome this, we need to move the data to a class method that resides in a separate module or class. This allows us to extend that module or class before its data is used, without having to place a prepend_if_ee in the middle of CE code.

For example, in one place we need to pass an extra argument to at_least_one_of so that the API could consider an EE-only argument as the least argument. We would approach this as follows:

# api/merge_requests/parameters.rb
module API
  class MergeRequests < Grape::API::Instance
    module Parameters
      def self.update_params_at_least_one_of
        %i[
          assignee_id
          description
        ]
      end
    end
  end
end

API::MergeRequests::Parameters.prepend_if_ee('EE::API::MergeRequests::Parameters')

# api/merge_requests.rb
module API
  class MergeRequests < Grape::API::Instance
    params do
      at_least_one_of(*Parameters.update_params_at_least_one_of)
    end
  end
end

And then we could easily extend that argument in the EE class method:

module EE
  module API
    module MergeRequests
      module Parameters
        extend ActiveSupport::Concern

        class_methods do
          extend ::Gitlab::Utils::Override

          override :update_params_at_least_one_of
          def update_params_at_least_one_of
            super.push(*%i[
              squash
            ])
          end
        end
      end
    end
  end
end

It could be annoying if we need this for a lot of routes, but it might be the simplest solution right now.

This approach can also be used when models define validations that depend on class methods. For example:

# app/models/identity.rb
class Identity < ActiveRecord::Base
  def self.uniqueness_scope
    [:provider]
  end

  prepend_if_ee('EE::Identity')

  validates :extern_uid,
    allow_blank: true,
    uniqueness: { scope: uniqueness_scope, case_sensitive: false }
end

# ee/app/models/ee/identity.rb
module EE
  module Identity
    extend ActiveSupport::Concern

    class_methods do
      extend ::Gitlab::Utils::Override

      def uniqueness_scope
        [*super, :saml_provider_id]
      end
    end
  end
end

Instead of taking this approach, we would refactor our code into the following:

# ee/app/models/ee/identity/uniqueness_scopes.rb
module EE
  module Identity
    module UniquenessScopes
      extend ActiveSupport::Concern

      class_methods do
        extend ::Gitlab::Utils::Override

        def uniqueness_scope
          [*super, :saml_provider_id]
        end
      end
    end
  end
end

# app/models/identity/uniqueness_scopes.rb
class Identity < ActiveRecord::Base
  module UniquenessScopes
    def self.uniqueness_scope
      [:provider]
    end
  end
end

Identity::UniquenessScopes.prepend_if_ee('EE::Identity::UniquenessScopes')

# app/models/identity.rb
class Identity < ActiveRecord::Base
  validates :extern_uid,
    allow_blank: true,
    uniqueness: { scope: Identity::UniquenessScopes.scopes, case_sensitive: false }
end

Code in spec/

When you're testing EE-only features, avoid adding examples to the existing CE specs. Also do not change existing CE examples, since they should remain working as-is when EE is running without a license.

Instead place EE specs in the ee/spec folder.

Code in spec/factories

Use FactoryBot.modify to extend factories already defined in CE.

Note that you cannot define new factories (even nested ones) inside the FactoryBot.modify block. You can do so in a separate FactoryBot.define block as shown in the example below:

# ee/spec/factories/notes.rb
FactoryBot.modify do
  factory :note do
    trait :on_epic do
      noteable { create(:epic) }
      project nil
    end
  end
end

FactoryBot.define do
  factory :note_on_epic, parent: :note, traits: [:on_epic]
end

JavaScript code in assets/javascripts/

To separate EE-specific JS-files we should also move the files into an ee folder.

For example there can be an app/assets/javascripts/protected_branches/protected_branches_bundle.js and an EE counterpart ee/app/assets/javascripts/protected_branches/protected_branches_bundle.js. The corresponding import statement would then look like this:

// app/assets/javascripts/protected_branches/protected_branches_bundle.js
import bundle from '~/protected_branches/protected_branches_bundle.js';

// ee/app/assets/javascripts/protected_branches/protected_branches_bundle.js
// (only works in EE)
import bundle from 'ee/protected_branches/protected_branches_bundle.js';

// in CE: app/assets/javascripts/protected_branches/protected_branches_bundle.js
// in EE: ee/app/assets/javascripts/protected_branches/protected_branches_bundle.js
import bundle from 'ee_else_ce/protected_branches/protected_branches_bundle.js';

See the frontend guide performance section for information on managing page-specific JavaScript within EE.

Vue code in assets/javascript

script tag

Child Component only used in EE

To separate Vue template differences we should async import the components.

Doing this allows for us to load the correct component in EE while in CE we can load a empty component that renders nothing. This code should exist in the CE repository as well as the EE repository.

<script>
export default {
  components: {
    EEComponent: () => import('ee_component/components/test.vue'),
  },
};
</script>

<template>
  <div>
    <ee-component />
  </div>
</template>

For JS code that is EE only, like props, computed properties, methods, etc

• Please do not use mixins unless ABSOLUTELY NECESSARY. Please try to find an alternative pattern.

Recommended alternative approach (named/scoped slots)

• We can use slots and/or scoped slots to achieve the same thing as we did with mixins. If you only need an EE component there is no need to create the CE component.

1. First, we have a CE component that can render a slot in case we need EE template and functionality to be decorated on top of the CE base.

// ./ce/my_component.vue

<script>
export default {
  props: {
    tooltipDefaultText: {
      type: String,
    },
  },
  computed: {
    tooltipText() {
      return this.tooltipDefaultText || "5 issues please";
    }
  },
}
</script>

<template>
  <span v-gl-tooltip :title="tooltipText" class="ce-text">Community Edition Only Text</span>
  <slot name="ee-specific-component">
</template>

1. Next, we render the EE component, and inside of the EE component we render the CE component and add additional content in the slot.

// ./ee/my_component.vue

<script>
export default {
  computed: {
    tooltipText() {
      if (this.weight) {
        return "5 issues with weight 10";
      }
    }
  },
  methods: {
    submit() {
      // do something.
    }
  },
}
</script>

<template>
  <my-component :tooltipDefaultText="tooltipText">
    <template #ee-specific-component>
      <span class="some-ee-specific">EE Specific Value</span>
      <button @click="submit">Click Me</button>
    </template>
  </my-component>
</template>

1. Finally, wherever the component is needed we can require it like so

import MyComponent from 'ee_else_ce/path/my_component'.vue

• this way the correct component will be included for either the ce or ee implementation

For EE components that need different results for the same computed values, we can pass in props to the CE wrapper as seen in the example.

• EE Child components

  • Since we are using the async loading to check which component to load, we'd still use the component's name, check this example.

• EE extra HTML

  • For the templates that have extra HTML in EE we should move it into a new component and use the ee_else_ce dynamic import

Non Vue Files

For regular JS files, the approach is similar.

1. We will keep using the ee_else_ce helper, this means that EE only code should be inside the ee/ folder.
   1. An EE file should be created with the EE only code, and it should extend the CE counterpart.
   2. For code inside functions that can't be extended, the code should be moved into a new file and we should use ee_else_ce helper:

Example

  import eeCode from 'ee_else_ce/ee_code';

  function test() {
    const test = 'a';

    eeCode();

    return test;
  }

SCSS code in assets/stylesheets

If a component you're adding styles for is limited to EE, it is better to have a separate SCSS file in an appropriate directory within app/assets/stylesheets.

In some cases, this is not entirely possible or creating dedicated SCSS file is an overkill, e.g. a text style of some component is different for EE. In such cases, styles are usually kept in a stylesheet that is common for both CE and EE, and it is wise to isolate such ruleset from rest of CE rules (along with adding comment describing the same) to avoid conflicts during CE to EE merge.

Bad

.section-body {
  .section-title {
    background: $gl-header-color;
  }

  &.ee-section-body {
    .section-title {
      background: $gl-header-color-cyan;
    }
  }
}

Good

.section-body {
  .section-title {
    background: $gl-header-color;
  }
}

// EE-specific start
.section-body.ee-section-body {
  .section-title {
    background: $gl-header-color-cyan;
  }
}
// EE-specific end

GitLab-svgs

Conflicts in app/assets/images/icons.json or app/assets/images/icons.svg can be resolved simply by regenerating those assets with yarn run svg.