[Fix #9244] When a cop defined in an extension is explicitly enabled, ensure that it remains enabled.

[dvandersluis]

With DisabledByDefault: true in a config, Enabled: false is automatically added to every key in the default configuration.

In normal operation, the configuration from any config files (including via inheritence) is then merged into that default configuration, so that if a cop is explicitly enabled it overrides the default disable (in ConfigLoaderResolver#merge_with_default). This works even if inherit_from or inherit_gem are specified.

However, extensions inject their configuration in when they are required, and the injection code that extensions use also calls merge_with_default. In that case, the extension's configuration gets merged into rubocop's default, which then becomes the default configuration (note, depending on how many extensions are required by the user, this process may happen multiple times). When that configuration gets the local config merged into it with DisabledByDefault: true, if that extension's configuration had a department config key, it would get Enabled: false set on it. Then, when the specific cop is checked for if it's enabled, the department value would override the local value, and the cop would be disabled.

In order to fix this, cops with Enabled: true in their configuration after all the merging happens are always considered to be enabled, and the department is not checked. To facilitate this, when config files are being merged (either through inheritence or through merge_with_default), if a department is disabled any previously defined cops that are Enabled are flipped to be disabled (as expected, since configurations are meant to override other configurations they inherit from).

---

Example:

# .rubocop.yml
require:
  - rubocop-rspec
  
AllCops:
  DisabledByDefault: true

RSpec/Focus:
  Enabled: true

Before:

$ rubocop test_spec.rb
Inspecting 1 file
.

1 file inspected, no offenses detected

After:

$ rubocop test_spec.rb
Inspecting 1 file
C

Offenses:

test_spec.rb:31:3: C: RSpec/Focus: Focused spec found.
  fit 'does something' do
  ^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected

Fixes #9244.

---

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[dvandersluis]

This bug is really an artifact of the lack of plugin system, which I have some ideas about how we can get into place. However, given that we need to keep supporting the existing injection system for backwards compatibility, this needed to be fixed regardless.

[dvandersluis]

The previous test was for a cop that wasn't actually pending anymore, so I updated it to not rely on the default config not changing.

[dvandersluis]

I expected the department calculation change in #9258 to affect this. Now that it's merged, I've updated to ensure that nested departments work as well. /cc @mvz @bbatsov

[bbatsov]

This bug is really an artifact of the lack of plugin system, which I have some ideas about how we can get into place.

You're totally right. That's one of the major items we kept discussing for years and never really got to doing. It's nice you're thinking in that direction.