Initial detection of Auto-DevOps buildable projects

Contains a large list of files we expect to find for an Auto-DevOps
project.

4 files changed, 141 insertions, 2 deletions

diff --git a/lib/gitlab/auto_devops/buildable_detector.rb b/lib/gitlab/auto_devops/buildable_detector.rb
new file mode 100644
index 00000000000..68f29f8bc34
--- /dev/null
+++ b/lib/gitlab/auto_devops/buildable_detector.rb
@@ -0,0 +1,103 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module AutoDevops
+    class BuildableDetector
+      VARIABLES = [
+        'BUILDPACK_URL'
+      ].freeze
+
+      FILE_PATTERNS = [
+        'Dockerfile',
+
+        # https://github.com/heroku/heroku-buildpack-clojure
+        'project.clj',
+
+        # https://github.com/heroku/heroku-buildpack-go
+        'go.mod',
+        'Gopkg.mod',
+        'Godeps/Godeps.json',
+        'vendor/vendor.json',
+        'glide.yaml',
+        'src/**.go',
+
+        # https://github.com/heroku/heroku-buildpack-gradle
+        'gradlew',
+        'build.gradle',
+        'settings.gradle',
+
+        # https://github.com/heroku/heroku-buildpack-java
+        'pom.xml',
+        'pom.atom',
+        'pom.clj',
+        'pom.groovy',
+        'pom.rb',
+        'pom.scala',
+        'pom.yaml',
+        'pom.yml',
+
+        # https://github.com/heroku/heroku-buildpack-multi
+        '.buildpacks',
+
+        # https://github.com/heroku/heroku-buildpack-nodejs
+        'package.json',
+
+        # https://github.com/heroku/heroku-buildpack-php
+        'composer.json',
+        'index.php',
+
+        # https://github.com/heroku/heroku-buildpack-play
+        # TODO: detect script excludes some scala files
+        '*/conf/application.conf',
+        '*modules*',
+
+        # https://github.com/heroku/heroku-buildpack-python
+        # TODO: detect script checks that all of these exist, not any
+        'requirements.txt',
+        'setup.py',
+        'Pipfile',
+
+        # https://github.com/heroku/heroku-buildpack-ruby
+        'Gemfile',
+
+        # https://github.com/heroku/heroku-buildpack-scala
+        '*.sbt',
+        'project/*.scala',
+        '.sbt/*.scala',
+        'project/build.properties',
+
+        # https://github.com/dokku/buildpack-nginx
+        '.static'
+      ].freeze
+
+      def initialize(project, ref)
+        @project = project
+        @ref = ref
+      end
+
+      def buildable?
+        detected_variables? || detected_files?
+      end
+
+      private
+
+      attr_accessor :project, :ref
+
+      def detected_variables?
+        project.ci_variables_for(ref: ref).exists?(key: VARIABLES) # rubocop:disable CodeReuse/ActiveRecord
+      end
+
+      def detected_files?
+        return if !ref && !project.repository.root_ref
+
+        project.repository.ls_files(ref).find do |filename|
+          FILE_PATTERNS.any? do |pattern|
+            File.fnmatch?(pattern, filename, File::FNM_CASEFOLD)
+          end
+        end
+      rescue GRPC::NotFound
+        false
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/ci/build/prerequisite/auto_devops_buildable.rb b/lib/gitlab/ci/build/prerequisite/auto_devops_buildable.rb
new file mode 100644
index 00000000000..1c03be32d19
--- /dev/null
+++ b/lib/gitlab/ci/build/prerequisite/auto_devops_buildable.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Build
+      module Prerequisite
+        class AutoDevopsBuildable < Base
+          def unmet?
+            build.project.auto_devops_enabled? &&
+              !build.project.has_auto_devops_explicitly_enabled? &&
+              build.pipeline.auto_devops_buildable.nil? &&
+              build.pipeline.auto_devops_source?
+          end
+
+          def complete!
+            return unless unmet?
+
+            build.pipeline.update!(auto_devops_buildable: auto_devops_buildable?)
+
+            throw :unsupported unless build.pipeline.auto_devops_buildable?
+          end
+
+          private
+
+          def auto_devops_buildable?
+            !!Gitlab::AutoDevops::BuildableDetector.new(build.project, build.pipeline.sha).buildable?
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/ci/build/prerequisite/factory.rb b/lib/gitlab/ci/build/prerequisite/factory.rb
index 60cdf7af418..a42c88ded58 100644
--- a/lib/gitlab/ci/build/prerequisite/factory.rb
+++ b/lib/gitlab/ci/build/prerequisite/factory.rb
@@ -8,7 +8,7 @@ module Gitlab
           attr_reader :build
 
           def self.prerequisites
-            [KubernetesNamespace]
+            [KubernetesNamespace, AutoDevopsBuildable]
           end
 
           def initialize(build)
diff --git a/lib/gitlab/ci/pipeline/chain/validate/config.rb b/lib/gitlab/ci/pipeline/chain/validate/config.rb
index 28c38cc3d18..a6f63eabb80 100644
--- a/lib/gitlab/ci/pipeline/chain/validate/config.rb
+++ b/lib/gitlab/ci/pipeline/chain/validate/config.rb
@@ -11,7 +11,11 @@ module Gitlab
             def perform!
               unless @pipeline.config_processor
                 unless @pipeline.ci_yaml_file
-                  return error("Missing #{@pipeline.ci_yaml_file_path} file")
+                  if @pipeline.project.auto_devops_enabled?
+                    return error("Auto-DevOps enabled but no buildable files found")
+                  else
+                    return error("Missing #{@pipeline.ci_yaml_file_path} file")
+                  end
                 end
 
                 if @command.save_incompleted && @pipeline.has_yaml_errors?