Use variables collection as build predefined variables

app/models/ci/build.rb

@@ -252,23 +252,25 @@ module Ci
     # All variables, including those dependent on environment, which could
     # contain unexpanded variables.
     def variables(environment: persisted_environment)
-      variables = predefined_variables
-      variables += project.predefined_variables
-      variables += pipeline.predefined_variables
-      variables += runner.predefined_variables if runner
-      variables += project.container_registry_variables
-      variables += project.deployment_variables if has_environment?
-      variables += project.auto_devops_variables
-      variables += yaml_variables
-      variables += user_variables
-      variables += project.group.secret_variables_for(ref, project).map(&:to_runner_variable) if project.group
-      variables += secret_variables(environment: environment)
-      variables += trigger_request.user_variables if trigger_request
-      variables += pipeline.variables.map(&:to_runner_variable)
-      variables += pipeline.pipeline_schedule.job_variables if pipeline.pipeline_schedule
-      variables += persisted_environment_variables if environment
-
-      variables
+      collection = Gitlab::Ci::Variables::Collection.new.tap do |variables|
+        variables.concat(predefined_variables)
+        variables.concat(project.predefined_variables)
+        variables.concat(pipeline.predefined_variables)
+        variables.concat(runner.predefined_variables) if runner
+        variables.concat(project.container_registry_variables)
+        variables.concat(project.deployment_variables) if has_environment?
+        variables.concat(project.auto_devops_variables)
+        variables.concat(yaml_variables)
+        variables.concat(user_variables)
+        variables.concat(project.group.secret_variables_for(ref, project).map(&:to_runner_variable)) if project.group
+        variables.concat(secret_variables(environment: environment))
+        variables.concat(trigger_request.user_variables) if trigger_request
+        variables.concat(pipeline.variables)
+        variables.concat(pipeline.pipeline_schedule.job_variables) if pipeline.pipeline_schedule
+        variables.concat(persisted_environment_variables) if environment
+      end
+
+      collection.to_runner_variables
     end
 
     def features

app/models/concerns/has_variable.rb

@@ -20,8 +20,12 @@ module HasVariable
       super(new_key.to_s.strip)
     end
 
-    def to_runner_variable
+    def to_hash
       { key: key, value: value, public: false }
     end
+
+    def to_runner_variable
+      to_hash
+    end
   end
 end

app/models/project.rb

@@ -1571,15 +1571,17 @@ class Project < ActiveRecord::Base
   end
 
   def predefined_variables
-    [
-      { key: 'CI_PROJECT_ID', value: id.to_s, public: true },
-      { key: 'CI_PROJECT_NAME', value: path, public: true },
-      { key: 'CI_PROJECT_PATH', value: full_path, public: true },
-      { key: 'CI_PROJECT_PATH_SLUG', value: full_path_slug, public: true },
-      { key: 'CI_PROJECT_NAMESPACE', value: namespace.full_path, public: true },
-      { key: 'CI_PROJECT_URL', value: web_url, public: true },
-      { key: 'CI_PROJECT_VISIBILITY', value: Gitlab::VisibilityLevel.string_level(visibility_level), public: true }
-    ]
+    visibility = Gitlab::VisibilityLevel.string_level(visibility_level)
+
+    Gitlab::Ci::Variables::Collection.new.tap do |variables|
+      variables.append(key: 'CI_PROJECT_ID', value: id.to_s, public: true)
+      variables.append(key: 'CI_PROJECT_NAME', value: path, public: true)
+      variables.append(key: 'CI_PROJECT_PATH', value: full_path, public: true)
+      variables.append(key: 'CI_PROJECT_PATH_SLUG', value: full_path_slug, public: true)
+      variables.append(key: 'CI_PROJECT_NAMESPACE', value: namespace.full_path, public: true)
+      variables.append(key: 'CI_PROJECT_URL', value: web_url, public: true)
+      variables.append(key: 'CI_PROJECT_VISIBILITY', value: visibility, public: true)
+    end
   end
 
   def container_registry_variables

lib/gitlab/ci/variables/collection.rb

@@ -7,13 +7,17 @@ module Gitlab
         def initialize(variables = [])
           @variables = []
 
-          variables.each { |variable| append(variable) }
+          variables.each { |variable| self.append(variable) }
         end
 
         def append(resource)
           @variables.append(Collection::Item.fabricate(resource))
         end
 
+        def concat(resources)
+          resources.each { |variable| self.append(variable) }
+        end
+
         def each
           @variables.each { |variable| yield variable }
         end

lib/gitlab/ci/variables/collection/item.rb

@@ -33,10 +33,12 @@ module Gitlab
               self.new(resource)
             when ::Ci::Variable
               self.new(resource.to_hash)
+            when ::Ci::PipelineVariable
+              self.new(resource.to_hash)
             when self
               resource.dup
             else
-              raise ArgumentError, 'Unknown CI/CD variable resource!'
+              raise ArgumentError, "Unknown `#{resource.class}` variable resource!"
             end
           end
         end