summaryrefslogtreecommitdiff
path: root/doc/development/ee_features.md
blob: d716325f3322fb8838571864afcf91e4d8e0635d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
# 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.
- **Submit a MR to the `www-gitlab-com` project.**: Add the new feature to the
  [EE features list](https://about.gitlab.com/features/).

## Act as CE when unlicensed

Since the implementation of [GitLab CE features to work with unlicensed EE instance][ee-as-ce]
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](https://gitlab.com/gitlab-org/gitlab/blob/master/config/helpers/is_ee_env.js)
to something that evaluates as `true`. The same works for running tests
(for example `FOSS_ONLY=1 yarn jest`).

[ee-as-ce]: https://gitlab.com/gitlab-org/gitlab/issues/2500

## 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.

[`config/application.rb`]: https://gitlab.com/gitlab-org/gitlab/blob/925d3d4ebc7a2c72964ce97623ae41b8af12538d/config/application.rb#L42-52

### 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:

```ruby
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`

#### 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`](utilities.md#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 behaviour 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](https://en.wikipedia.org/wiki/Template_method_pattern).
  For example, given this base:

  ```ruby
    class Base
      def execute
        return unless enabled?

        # ...
        # ...
      end
    end
  ```

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

  ```ruby
    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:

  ```ruby
    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
  ```

  This would require updating CE first, or make sure this is back ported to CE.

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`:

```ruby
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:

```ruby
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:

```ruby
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:

```ruby
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:

```ruby
def internal?
  ghost?
end
```

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

```ruby
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`:

```ruby
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:

```ruby
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.

#### 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.

```haml
- # 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`:

``` 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](https://github.com/ruby-grape/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-features-based-on-ce-features).

#### EE API routes

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

```ruby
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 params

We can define `params` and utilize `use` in another `params` definition to
include params 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 params for EE. We can move the
params out of the `Grape::API` class to a helper module, so we can inject it
before it would be used in the class.

```ruby
module API
  class Projects < Grape::API
    helpers Helpers::ProjectsHelpers
  end
end
```

Given this CE API `params`:

```ruby
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:

```ruby
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:

```ruby
module API
  class JobArtifacts < Grape::API
    # 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:

```ruby
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 behaviour

Sometimes we need EE-specific behaviour 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:

```ruby
module API
  class MergeRequests < Grape::API
    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:

```ruby
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:

```ruby
# api/merge_requests/parameters.rb
module API
  class MergeRequests < Grape::API
    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
    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:

```ruby
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:

```ruby
# 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:

```ruby
# 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:

```ruby
# 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:

```javascript
// 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](fe_guide/performance.md) 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](https://vuejs.org/v2/guide/components-dynamic-async.html#Async-Components).

Doing this allows for us to load the correct component in EE whilst 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.

```html
<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, we will keep the current approach

- Since we [can't async load a mixin](https://github.com/vuejs/vue-loader/issues/418#issuecomment-254032223) we will use the [`ee_else_ce`](../development/ee_features.md#javascript-code-in-assetsjavascripts) alias we already have for webpack.
  - This means all the EE specific props, computed properties, methods, etc that are EE only should be in a mixin in the `ee/` folder and we need to create a CE counterpart of the mixin

##### Example

```javascript
import mixin from 'ee_else_ce/path/mixin';

{
    mixins: [mixin]
}
```

- Computed Properties/methods and getters only used in the child import still need a counterpart in CE

- For store modules, we will need a CE counterpart too.
- You can see an MR with an example [here](https://gitlab.com/gitlab-org/gitlab/merge_requests/9762)

#### `template` tag

- **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](#child-component-only-used-in-ee).

- **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`](../development/ee_features.md#javascript-code-in-assetsjavascripts) 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.
   1. 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

```javascript
  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 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

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

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

### Good

```scss
.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`](https://gitlab.com/gitlab-org/gitlab-svgs).