Add global rules to match herokuish detect for Auto-DevOps

This adds a long list of filename rules to decide if Auto-DevOps is
likely to work or not.

changelogs/unreleased/dont_run_auto_devops.yml

+---
+title: Don't run Auto DevOps when no dockerfile or matching buildpack exists
+merge_request: 20267
+author:
+type: changed

ee/spec/requests/api/triggers_spec.rb

@@ -4,7 +4,7 @@ require 'spec_helper'
 
 describe API::Triggers do
   let(:user) { create(:user) }
-  let(:project) { create(:project, :repository, creator: user) }
+  let(:project) { create(:project, :repository, :auto_devops, creator: user) }
 
   describe 'POST /projects/:project_id/trigger/pipeline' do
     context 'when triggering a pipeline from a job token' do

ee/spec/services/merge_trains/create_pipeline_service_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 describe MergeTrains::CreatePipelineService do
-  let(:project) { create(:project, :repository) }
+  let(:project) { create(:project, :repository, :auto_devops) }
   set(:maintainer) { create(:user) }
   let(:service) { described_class.new(project, maintainer) }
   let(:previous_ref) { 'refs/heads/master' }

lib/gitlab/ci/templates/Auto-DevOps.gitlab-ci.yml

@@ -72,6 +72,83 @@ stages:
   - performance
   - cleanup
 
+workflow:
+  rules:
+    - if: '$BUILDPACK_URL || $AUTO_DEVOPS_EXPLICITLY_ENABLED == "1"'
+
+    - exists:
+        - Dockerfile
+
+    # https://github.com/heroku/heroku-buildpack-clojure
+    - exists:
+        - project.clj
+
+    # https://github.com/heroku/heroku-buildpack-go
+    - exists:
+        - go.mod
+        - Gopkg.mod
+        - Godeps/Godeps.json
+        - vendor/vendor.json
+        - glide.yaml
+        - src/**/*.go
+
+    # https://github.com/heroku/heroku-buildpack-gradle
+    - exists:
+        - gradlew
+        - build.gradle
+        - settings.gradle
+
+    # https://github.com/heroku/heroku-buildpack-java
+    - exists:
+        - pom.xml
+        - pom.atom
+        - pom.clj
+        - pom.groovy
+        - pom.rb
+        - pom.scala
+        - pom.yaml
+        - pom.yml
+
+    # https://github.com/heroku/heroku-buildpack-multi
+    - exists:
+        - .buildpacks
+
+    # https://github.com/heroku/heroku-buildpack-nodejs
+    - exists:
+        - package.json
+
+    # https://github.com/heroku/heroku-buildpack-php
+    - exists:
+        - composer.json
+        - index.php
+
+    # https://github.com/heroku/heroku-buildpack-play
+    # TODO: detect script excludes some scala files
+    - exists:
+        - '**/conf/application.conf'
+
+    # https://github.com/heroku/heroku-buildpack-python
+    # TODO: detect script checks that all of these exist, not any
+    - exists:
+        - requirements.txt
+        - setup.py
+        - Pipfile
+
+    # https://github.com/heroku/heroku-buildpack-ruby
+    - exists:
+        - Gemfile
+
+    # https://github.com/heroku/heroku-buildpack-scala
+    - exists:
+        - '*.sbt'
+        - project/*.scala
+        - .sbt/*.scala
+        - project/build.properties
+
+    # https://github.com/dokku/buildpack-nginx
+    - exists:
+        - .static
+
 include:
   - template: Jobs/Build.gitlab-ci.yml  # https://gitlab.com/gitlab-org/gitlab-foss/blob/master/lib/gitlab/ci/templates/Jobs/Build.gitlab-ci.yml
   - template: Jobs/Test.gitlab-ci.yml  # https://gitlab.com/gitlab-org/gitlab-foss/blob/master/lib/gitlab/ci/templates/Jobs/Test.gitlab-ci.yml

spec/lib/gitlab/ci/templates/auto_devops_gitlab_ci_yaml_spec.rb

@@ -9,7 +9,7 @@ describe 'Auto-DevOps.gitlab-ci.yml' do
     let(:user) { create(:admin) }
     let(:default_branch) { 'master' }
     let(:pipeline_branch) { default_branch }
-    let(:project) { create(:project, :custom_repo, files: { 'README.md' => '' }) }
+    let(:project) { create(:project, :auto_devops, :custom_repo, files: { 'README.md' => '' }) }
     let(:service) { Ci::CreatePipelineService.new(project, user, ref: pipeline_branch ) }
     let(:pipeline) { service.execute!(:push) }
     let(:build_names) { pipeline.builds.pluck(:name) }
@@ -107,4 +107,50 @@ describe 'Auto-DevOps.gitlab-ci.yml' do
       end
     end
   end
+
+  describe 'build-pack detection' do
+    using RSpec::Parameterized::TableSyntax
+
+    where(:case_name, :files, :variables, :include_build_names, :not_include_build_names) do
+      'No match'        | { 'README.md' => '' }                   | {}                                          | %w()           | %w(build test)
+      'Buildpack'       | { 'README.md' => '' }                   | { 'BUILDPACK_URL' => 'http://example.com' } | %w(build test) | %w()
+      'Explicit set'    | { 'README.md' => '' }                   | { 'AUTO_DEVOPS_EXPLICITLY_ENABLED' => '1' } | %w(build test) | %w()
+      'Explicit unset'  | { 'README.md' => '' }                   | { 'AUTO_DEVOPS_EXPLICITLY_ENABLED' => '0' } | %w()           | %w(build test)
+      'Dockerfile'      | { 'Dockerfile' => '' }                  | {}                                          | %w(build test) | %w()
+      'Clojure'         | { 'project.clj' => '' }                 | {}                                          | %w(build test) | %w()
+      'Go modules'      | { 'go.mod' => '' }                      | {}                                          | %w(build test) | %w()
+      'Go gb'           | { 'src/gitlab.com/gopackage.go' => '' } | {}                                          | %w(build test) | %w()
+      'Gradle'          | { 'gradlew' => '' }                     | {}                                          | %w(build test) | %w()
+      'Java'            | { 'pom.xml' => '' }                     | {}                                          | %w(build test) | %w()
+      'Multi-buildpack' | { '.buildpacks' => '' }                 | {}                                          | %w(build test) | %w()
+      'NodeJS'          | { 'package.json' => '' }                | {}                                          | %w(build test) | %w()
+      'PHP'             | { 'composer.json' => '' }               | {}                                          | %w(build test) | %w()
+      'Play'            | { 'conf/application.conf' => '' }       | {}                                          | %w(build test) | %w()
+      'Python'          | { 'Pipfile' => '' }                     | {}                                          | %w(build test) | %w()
+      'Ruby'            | { 'Gemfile' => '' }                     | {}                                          | %w(build test) | %w()
+      'Scala'           | { 'build.sbt' => '' }                   | {}                                          | %w(build test) | %w()
+      'Static'          | { '.static' => '' }                     | {}                                          | %w(build test) | %w()
+    end
+
+    with_them do
+      let(:user) { create(:admin) }
+      let(:project) { create(:project, :custom_repo, files: files) }
+      let(:service) { Ci::CreatePipelineService.new(project, user, ref: 'master' ) }
+      let(:pipeline) { service.execute(:push) }
+      let(:build_names) { pipeline.builds.pluck(:name) }
+
+      before do
+        stub_ci_pipeline_yaml_file(template.content)
+        allow_any_instance_of(Ci::BuildScheduleWorker).to receive(:perform).and_return(true)
+        variables.each do |(key, value)|
+          create(:ci_variable, project: project, key: key, value: value)
+        end
+      end
+
+      it 'creates a pipeline with the expected jobs' do
+        expect(build_names).to include(*include_build_names)
+        expect(build_names).not_to include(*not_include_build_names)
+      end
+    end
+  end
 end

spec/services/ci/create_pipeline_service_spec.rb

@@ -493,6 +493,7 @@ describe Ci::CreatePipelineService do
         before do
           stub_ci_pipeline_yaml_file(nil)
           allow_any_instance_of(Project).to receive(:auto_devops_enabled?).and_return(true)
+          create(:project_auto_devops, project: project)
         end
 
         it 'pull it from Auto-DevOps' do

spec/services/external_pull_requests/create_pipeline_service_spec.rb

@@ -4,7 +4,7 @@ require 'spec_helper'
 
 describe ExternalPullRequests::CreatePipelineService do
   describe '#execute' do
-    set(:project) { create(:project, :repository) }
+    set(:project) { create(:project, :auto_devops, :repository) }
     set(:user) { create(:user) }
     let(:pull_request) { create(:external_pull_request, project: project) }