Add metric instrumentation class generator

This adds a Rails generator for creating the new Usage Ping
instrumentation classes along with spec stubs.

Added generator files to Danger tracking.

Excluded RSpec/TopLevelDescribePath from fixtures to fix Rubocop treating
them like RSpec files.

Added docs for the instrumentation generator.

.rubocop.yml

@@ -90,6 +90,7 @@ RSpec/FilePath:
     - 'spec/frontend/fixtures/*'
     - 'ee/spec/frontend/fixtures/*'
     - 'spec/requests/api/v3/*'
+    - 'spec/fixtures/**/*'
 
 # Configuration parameters: AllowSubject.
 RSpec/MultipleMemoizedHelpers:
@@ -664,3 +665,8 @@ Style/RegexpLiteralMixedPreserve:
     - mixed
     - mixed_preserve
   EnforcedStyle: mixed_preserve
+
+RSpec/TopLevelDescribePath:
+  Exclude:
+    - 'spec/fixtures/**/*.rb'
+    - 'ee/spec/fixtures/**/*.rb'

doc/development/usage_ping/metrics_instrumentation.md

@@ -85,3 +85,18 @@ module Gitlab
   end
 end
 ```
+
+## Creating a new metric instrumentation class
+
+To create a stub instrumentation for a Usage Ping metric, you can use a dedicated [generator](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/generators/gitlab/usage_metric_generator.rb):
+
+The generator takes the class name as an argument and the following options:
+
+- `--type=TYPE` Required. Indicates the metric type. It must be one of: `database`, `generic`, `redis_hll`.
+- `--ee` Indicates if the metric is for EE.
+
+```shell
+rails generate gitlab:usage_metric CountIssues --type database
+        create lib/gitlab/usage/metrics/instrumentations/count_issues_metric.rb
+        create spec/lib/gitlab/usage/metrics/instrumentations/count_issues_metric_spec.rb
+```

lib/generators/gitlab/usage_metric/USAGE

+Description:
+    Creates a stub instrumentation for a Service Ping metric
+
+Example:
+    rails generate gitlab:usage_metric CountIssues --type database
+
+    This will create:
+        lib/gitlab/usage/metrics/instrumentations/count_issues_metric.rb
+        spec/lib/gitlab/usage/metrics/instrumentations/count_issues_metric_spec.rb

lib/generators/gitlab/usage_metric/templates/instrumentation_class.rb.template

+# frozen_string_literal: true
+
+module Gitlab
+  module Usage
+    module Metrics
+      module Instrumentations
+        class <%= class_name %>Metric < <%= metric_superclass %>Metric
+          def value
+          end
+        end
+      end
+    end
+  end
+end

lib/generators/gitlab/usage_metric/templates/instrumentation_class_spec.rb.template

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Usage::Metrics::Instrumentations::<%= class_name %>Metric do
+  it_behaves_like 'a correct instrumented metric value', {}, 1
+end

lib/generators/gitlab/usage_metric/usage_metric_generator.rb

+# frozen_string_literal: true
+
+require 'rails/generators'
+
+module Gitlab
+  class UsageMetricGenerator < Rails::Generators::Base
+    CE_DIR = 'lib/gitlab/usage/metrics/instrumentations'
+    EE_DIR = 'ee/lib/ee/gitlab/usage/metrics/instrumentations'
+    SPEC_CE_DIR = 'spec/lib/gitlab/usage/metrics/instrumentations'
+    SPEC_EE_DIR = 'ee/spec/lib/ee/gitlab/usage/metrics/instrumentations'
+
+    ALLOWED_SUPERCLASSES = {
+      generic: 'Generic',
+      database: 'Database',
+      redis_hll: 'RedisHLL'
+    }.freeze
+
+    source_root File.expand_path('templates', __dir__)
+
+    class_option :ee, type: :boolean, optional: true, default: false, desc: 'Indicates if instrumentation is for EE'
+    class_option :type, type: :string, desc: "Metric type, must be one of: #{ALLOWED_SUPERCLASSES.keys.join(', ')}"
+
+    argument :class_name, type: :string, desc: 'Instrumentation class name, e.g.: CountIssues'
+
+    def create_class_files
+      validate!
+
+      template "instrumentation_class.rb.template", file_path
+      template "instrumentation_class_spec.rb.template", spec_file_path
+    end
+
+    private
+
+    def validate!
+      raise ArgumentError, "Type is required, valid options are #{ALLOWED_SUPERCLASSES.keys.join(', ')}" unless type.present?
+      raise ArgumentError, "Unknown type '#{type}', valid options are #{ALLOWED_SUPERCLASSES.keys.join(', ')}" if metric_superclass.nil?
+    end
+
+    def ee?
+      options[:ee]
+    end
+
+    def type
+      options[:type]
+    end
+
+    def file_path
+      dir = ee? ? EE_DIR : CE_DIR
+
+      File.join(dir, file_name)
+    end
+
+    def spec_file_path
+      dir = ee? ? SPEC_EE_DIR : SPEC_CE_DIR
+
+      File.join(dir, spec_file_name)
+    end
+
+    def file_name
+      "#{class_name.underscore}_metric.rb"
+    end
+
+    def spec_file_name
+      "#{class_name.underscore}_metric_spec.rb"
+    end
+
+    def metric_superclass
+      ALLOWED_SUPERCLASSES[type.to_sym]
+    end
+  end
+end

spec/fixtures/lib/generators/gitlab/usage_metric_generator/sample_metric.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Usage
+    module Metrics
+      module Instrumentations
+        class CountFooMetric < RedisHLLMetric
+          def value
+          end
+        end
+      end
+    end
+  end
+end

spec/fixtures/lib/generators/gitlab/usage_metric_generator/sample_metric_test.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Usage::Metrics::Instrumentations::CountFooMetric do
+  it_behaves_like 'a correct instrumented metric value', {}, 1
+end

spec/lib/generators/gitlab/usage_metric_generator_spec.rb

+# frozen_string_literal: true
+
+require 'generator_helper'
+
+RSpec.describe Gitlab::UsageMetricGenerator do
+  let(:ce_temp_dir) { Dir.mktmpdir }
+  let(:ee_temp_dir) { Dir.mktmpdir }
+  let(:spec_ce_temp_dir) { Dir.mktmpdir }
+  let(:spec_ee_temp_dir) { Dir.mktmpdir }
+  let(:args) { ['CountFoo'] }
+  let(:options) { { 'type' => 'redis_hll' } }
+
+  before do
+    stub_const("#{described_class}::CE_DIR", ce_temp_dir)
+    stub_const("#{described_class}::EE_DIR", ee_temp_dir)
+    stub_const("#{described_class}::SPEC_CE_DIR", spec_ce_temp_dir)
+    stub_const("#{described_class}::SPEC_EE_DIR", spec_ee_temp_dir)
+  end
+
+  after do
+    FileUtils.rm_rf([ce_temp_dir, ee_temp_dir, spec_ce_temp_dir, spec_ee_temp_dir])
+  end
+
+  describe 'Creating metric instrumentation files' do
+    let(:sample_metric_dir) { 'lib/generators/gitlab/usage_metric_generator' }
+    let(:sample_metric) { fixture_file(File.join(sample_metric_dir, 'sample_metric.rb')) }
+    let(:sample_spec) { fixture_file(File.join(sample_metric_dir, 'sample_metric_test.rb')) }
+
+    it 'creates CE metric instrumentation file using the template' do
+      described_class.new(args, options).invoke_all
+
+      file_path = File.join(ce_temp_dir, 'count_foo_metric.rb')
+      file = File.read(file_path)
+
+      expect(file).to eq(sample_metric)
+    end
+
+    it 'creates CE metric instrumentation spec file using the template' do
+      described_class.new(args, options).invoke_all
+
+      file_path = File.join(spec_ce_temp_dir, 'count_foo_metric_spec.rb')
+      file = File.read(file_path)
+
+      expect(file).to eq(sample_spec)
+    end
+
+    context 'with EE flag true' do
+      let(:options) { { 'type' => 'redis_hll', 'ee' => true } }
+
+      it 'creates EE metric instrumentation file using the template' do
+        described_class.new(args, options).invoke_all
+
+        file_path = File.join(ee_temp_dir, 'count_foo_metric.rb')
+        file = File.read(file_path)
+
+        expect(file).to eq(sample_metric)
+      end
+
+      it 'creates EE metric instrumentation spec file using the template' do
+        described_class.new(args, options).invoke_all
+
+        file_path = File.join(spec_ee_temp_dir, 'count_foo_metric_spec.rb')
+        file = File.read(file_path)
+
+        expect(file).to eq(sample_spec)
+      end
+    end
+
+    context 'with type option missing' do
+      let(:options) { {} }
+
+      it 'raises an ArgumentError' do
+        expect { described_class.new(args, options).invoke_all }.to raise_error(ArgumentError, /Type is required/)
+      end
+    end
+
+    context 'with type option value not included in approved superclasses' do
+      let(:options) { { 'type' => 'some_other_type' } }
+
+      it 'raises an ArgumentError' do
+        expect { described_class.new(args, options).invoke_all }.to raise_error(ArgumentError, /Unknown type 'some_other_type'/)
+      end
+    end
+  end
+end

tooling/danger/product_intelligence.rb

@@ -17,8 +17,10 @@ module Tooling
         'app/assets/javascripts/tracking.js',
         'spec/frontend/tracking_spec.js',
         'generator_templates/usage_metric_definition/metric_definition.yml',
+        'lib/generators/gitlab/usage_metric/usage_metric_generator.rb',
         'lib/generators/gitlab/usage_metric_definition_generator.rb',
         'lib/generators/gitlab/usage_metric_definition/redis_hll_generator.rb',
+        'spec/lib/generators/gitlab/usage_metric_generator_spec.rb',
         'spec/lib/generators/gitlab/usage_metric_definition_generator_spec.rb',
         'spec/lib/generators/gitlab/usage_metric_definition/redis_hll_generator_spec.rb',
         'config/metrics/schema.json'