Add CI variable to show when Auto-DevOps is explicitly enabled

app/models/project_auto_devops.rb

@@ -16,6 +16,7 @@ class ProjectAutoDevops < ApplicationRecord
 
   def predefined_variables
     Gitlab::Ci::Variables::Collection.new.tap do |variables|
+      variables.append(key: 'AUTO_DEVOPS_EXPLICITLY_ENABLED', value: '1') if enabled?
       variables.concat(deployment_strategy_default_variables)
     end
   end

changelogs/unreleased/auto_devops_enabled_ci_variable.yml

+---
+title: Add CI variable to show when Auto-DevOps is explicitly enabled
+merge_request: 20332
+author:
+type: changed

spec/models/project_auto_devops_spec.rb

@@ -23,7 +23,8 @@ describe ProjectAutoDevops do
         [
           { key: 'INCREMENTAL_ROLLOUT_MODE', value: 'manual' },
           { key: 'STAGING_ENABLED', value: '1' },
-          { key: 'INCREMENTAL_ROLLOUT_ENABLED', value: '1' }
+          { key: 'INCREMENTAL_ROLLOUT_ENABLED', value: '1' },
+          { key: 'AUTO_DEVOPS_EXPLICITLY_ENABLED', value: '1' }
         ]
       end
 
@@ -33,6 +34,8 @@ describe ProjectAutoDevops do
     context 'when deploy_strategy is continuous' do
       let(:auto_devops) { build_stubbed(:project_auto_devops, :continuous_deployment, project: project) }
 
+      it { expect(auto_devops.predefined_variables).to include(key: 'AUTO_DEVOPS_EXPLICITLY_ENABLED', value: '1') }
+
       it do
         expect(auto_devops.predefined_variables.map { |var| var[:key] })
           .not_to include("STAGING_ENABLED", "INCREMENTAL_ROLLOUT_ENABLED")
@@ -44,11 +47,19 @@ describe ProjectAutoDevops do
 
       it { expect(auto_devops.predefined_variables).to include(key: 'INCREMENTAL_ROLLOUT_MODE', value: 'timed') }
 
+      it { expect(auto_devops.predefined_variables).to include(key: 'AUTO_DEVOPS_EXPLICITLY_ENABLED', value: '1') }
+
       it do
         expect(auto_devops.predefined_variables.map { |var| var[:key] })
           .not_to include("STAGING_ENABLED", "INCREMENTAL_ROLLOUT_ENABLED")
       end
     end
+
+    context 'when auto-devops is explicitly disabled' do
+      let(:auto_devops) { build_stubbed(:project_auto_devops, :disabled, project: project) }
+
+      it { expect(auto_devops.predefined_variables.to_hash).to be_empty }
+    end
   end
 
   describe '#create_gitlab_deploy_token' do