Add API::Helpers::Version and expose API root URL

This commits adds a new class that is supposed to represent Grape API
version, like `v3` or `v4`.

app/models/project.rb

@@ -1700,6 +1700,15 @@ class Project < ActiveRecord::Base
       .append(key: 'CI_PROJECT_VISIBILITY', value: visibility)
       .concat(container_registry_variables)
       .concat(auto_devops_variables)
+      # .concat(api_variables)
+  end
+
+  def api_variables
+    Gitlab::Ci::Variables::Collection.new.tap do |variables|
+      API::Helpers::Version.new('v4').tap do |version|
+        variables.append(key: 'CI_API_V4_URL', value: version.root_url)
+      end
+    end
   end
 
   def container_registry_variables

lib/api/api.rb

@@ -10,14 +10,6 @@ module API
     NAMESPACE_OR_PROJECT_REQUIREMENTS = { id: NO_SLASH_URL_PART_REGEX }.freeze
     COMMIT_ENDPOINT_REQUIREMENTS = NAMESPACE_OR_PROJECT_REQUIREMENTS.merge(sha: NO_SLASH_URL_PART_REGEX).freeze
 
-    def self.root_path(version: 'v4')
-      unless versions.include?(version)
-        raise ArgumentError, 'Unknown API version!'
-      end
-
-      File.join('/', prefix.to_s, version.to_s)
-    end
-
     insert_before Grape::Middleware::Error,
                   GrapeLogging::Middleware::RequestLogger,
                   logger: Logger.new(LOG_FILENAME),

lib/api/helpers/version.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module API
+  module Helpers
+    class Version
+      include Helpers::RelatedResourcesHelpers
+
+      def initialize(version)
+        @version = version.to_s
+
+        unless API.versions.include?(version)
+          raise ArgumentError, 'Unknown API version!'
+        end
+      end
+
+      def root_path
+        File.join('/', API.prefix.to_s, @version)
+      end
+
+      def root_url
+        expose_url(root_path)
+      end
+
+      def to_s
+        @version
+      end
+    end
+  end
+end

spec/lib/api/api_spec.rb

@@ -15,22 +15,7 @@ describe API::API do
 
   describe '.versions' do
     it 'returns all available versions' do
-      expect(described_class.versions).to eq ['v3', 'v4']
-    end
-  end
-
-  describe '.root_path' do
-    it 'returns predefined API version path' do
-      expect(described_class.root_path).to eq '/api/v4'
-    end
-
-    it 'returns a version provided as keyword argument' do
-      expect(described_class.root_path(version: 'v3')).to eq '/api/v3'
-    end
-
-    it 'raises an error if version is not known' do
-      expect { described_class.root_path(version: 'v10') }
-        .to raise_error ArgumentError
+      expect(described_class.versions).to eq %w[v3 v4]
     end
   end
 end

spec/lib/api/helpers/version_spec.rb

@@ -0,0 +1,26 @@
+require 'spec_helper'
+
+describe API::Helpers::Version do
+  describe '.new' do
+    it 'is possible to initialize it with existing API version' do
+      expect(described_class.new('v4').to_s).to eq 'v4'
+    end
+
+    it 'raises an error when unsupported API version is provided' do
+      expect { described_class.new('v111') }.to raise_error ArgumentError
+    end
+  end
+
+  describe '#root_path' do
+    it 'returns a root path of the API version' do
+      expect(described_class.new('v4').root_path).to eq '/api/v4'
+    end
+  end
+
+  describe '#root_url' do
+    it 'returns an URL for a root path for the API version' do
+      expect(described_class.new('v4').root_url)
+        .to match %r{^http?://.*/api/v4$}
+    end
+  end
+end

spec/models/project_spec.rb

@@ -3496,7 +3496,29 @@ describe Project do
     end
   end
 
-  context '#auto_devops_variables' do
+  describe '#api_variables' do
+    set(:project) { create(:project) }
+
+    it 'exposes API v4 URL' do
+      expect(project.api_variables.first[:key]).to eq 'CI_API_V4_URL'
+      expect(project.api_variables.first[:value]).to include '/api/v4'
+    end
+
+    it 'contains an URL variable for every supported API version' do
+      supported_versions = API::API.versions.select do |version|
+        API::API.routes.select { |route| route.version == version }.many?
+      end
+
+      required_variables = supported_versions.map do |version|
+        "CI_API_#{version.upcase}_URL"
+      end
+
+      expect(project.api_variables.map { |variable| variable[:key] })
+        .to contain_exactly(*required_variables)
+    end
+  end
+
+  describe '#auto_devops_variables' do
     set(:project) { create(:project) }
 
     subject { project.auto_devops_variables }