Allow Config File Inheritance

README.md

@@ -123,13 +123,16 @@ The settings in the `shipit.yml` file relate to the different things you can do
 * [Custom Tasks](#custom-tasks) (`tasks`)
 * [Custom links](#custom-links) (`links`)
 * [Review Process](#review-process) (`review.checklist`, `review.monitoring`, `review.checks`)
+* [Inherit From](#inherit-from)(`inherit_from`)
 
 All the settings in `shipit.yml` are optional. Most applications can be deployed from Shipit without any configuration.
 
 Also, if your repository is deployed different ways depending on the environment, you can have an alternative `shipit.yml` by including the environment name.
 
 For example for a stack like: `my-org/my-repo/staging`, `shipit.staging.yml` will have priority over `shipit.yml`.
 
+In order to reduce duplication across different environment specific files, you can specify an `inherit_from` key in your relevant `shipit.yml` file. This key expects a string of the file name to inherit from. If this key is specified, a deep-merge will be performed on the file therein, overwriting any duplicated values from the parent. See [Inherit From](#inherit-from)(`inherit_From`) for example.
+
 Lastly, if you override the `app_name` configuration in your Shipit deployment, `yourapp.yml` and `yourapp.staging.yml` will work.
 
 * * *
@@ -613,6 +616,42 @@ review:
     - bundle exec rake db:migrate:status
 ```
 
+<h3 id="inherit-from">Inherit From</h3>
+
+If the `inherit_from` key is specified, a deep-merge will be performed on the file therein, overwriting any duplicated values from the parent. Keys may be chained across files. Example:
+
+``` yaml
+# shipit.production.yml
+inherit_from: shipit.staging.yml
+
+machine:
+  environment:
+    PUBLIC: true
+```
+
+``` yaml
+# shipit.staging.yml
+inherit_from: shipit.yml
+
+deploy:
+  override:
+    - ./some_deployment_process.sh ${PUBLIC}
+```
+
+``` yaml
+# shipit.yml
+
+machine:
+  environment:
+    TEST: true
+    PUBLIC: false
+```
+
+Loading 'shipit.production.yml' would result in:
+```rb
+{"machine"=>{"environment"=>{"TEST"=>true, "PUBLIC"=>true}}, "deploy"=>{"override"=>["./some_deployment_process.sh ${PUBLIC}"]}}
+```
+
 <h3 id="shell-commands-timeout">Shell commands timeout</h3>
 
 All the shell commands can take an optional `timeout` parameter. This is the value in seconds that a command can be inactive before Shipit will terminate the task.

app/models/shipit/deploy_spec/file_system.rb

@@ -100,7 +100,8 @@ def load_config
           return { 'deploy' => { 'pre' => [shipit_not_obeying_bare_file_echo_command, 'exit 1'] } }
         end
 
-        read_config(config_file_path)
+        config_obj = read_config(config_file_path)
+        build_config(config_file_path, config_obj)
       end
 
       def shipit_file_names_in_priority_order
@@ -136,6 +137,20 @@ def app_name
         @app_name ||= Shipit.app_name.downcase
       end
 
+      SHIPIT_CONFIG_INHERIT_FROM_KEY = "inherit_from"
+      def build_config(path, config_obj)
+        return config_obj if config_obj.blank? || !config_obj.key?(SHIPIT_CONFIG_INHERIT_FROM_KEY)
+
+        inherits_from_path = path.dirname.join(config_obj.delete(SHIPIT_CONFIG_INHERIT_FROM_KEY))
+        if inherits_from_path.exist?
+          inherits_config_obj = read_config(inherits_from_path)
+          config_obj = inherits_config_obj.deep_merge(config_obj)
+          path = inherits_from_path
+        end
+
+        build_config(path, config_obj)
+      end
+
       def read_config(path)
         SafeYAML.load(path.read) if path.exist?
       end

test/models/shipit/deploy_spec/file_system_test.rb

@@ -63,6 +63,35 @@ class FileSystemTest < ActiveSupport::TestCase
         assert loaded_config["deploy"]["pre"].include?('exit 1')
       end
 
+      test '#load_config builds proper config if inherit_from is present' do
+        Shipit.expects(:respect_bare_shipit_file?).returns(true).at_least_once
+        stack = shipit_stacks(:shipit)
+        deploy_spec = Shipit::DeploySpec::FileSystem.new(Dir.tmpdir, stack)
+        deploy_spec.expects(:config_file_path).returns(Pathname.new(Dir.tmpdir) + '/shipit_1.yml').at_least_once
+        deploy_spec.expects(:read_config).returns(SafeYAML.load(deploy_spec_inherit_from_yaml), SafeYAML.load(deploy_spec_yaml)).at_least_once
+        Pathname.any_instance.stubs(:exist?).returns(true)
+        loaded_config = deploy_spec.send(:load_config)
+        assert loaded_config.key?("deploy")
+        assert loaded_config["deploy"].key?("pre")
+        assert loaded_config["deploy"]["pre"].include?("test 2")
+        assert loaded_config["deploy"]["override"].include?("test 11")
+        assert_not loaded_config.include?(Shipit::DeploySpec::FileSystem::SHIPIT_CONFIG_INHERIT_FROM_KEY)
+      end
+
+      test '#load_config builds valid config if inherit_from path is missing' do
+        Shipit.expects(:respect_bare_shipit_file?).returns(true).at_least_once
+        stack = shipit_stacks(:shipit)
+        deploy_spec = Shipit::DeploySpec::FileSystem.new(Dir.tmpdir, stack)
+        deploy_spec.expects(:config_file_path).returns(Pathname.new(Dir.tmpdir) + '/shipit_1.yml').at_least_once
+        deploy_spec.expects(:read_config).returns(SafeYAML.load(deploy_spec_inherit_from_yaml)).at_least_once
+        Pathname.any_instance.stubs(:exist?).returns(false)
+        loaded_config = deploy_spec.send(:load_config)
+        assert loaded_config.key?("deploy")
+        assert_not loaded_config["deploy"].include?("pre")
+        assert loaded_config["deploy"]["override"].include?("test 11")
+        assert_not loaded_config.include?(Shipit::DeploySpec::FileSystem::SHIPIT_CONFIG_INHERIT_FROM_KEY)
+      end
+
       def deploy_spec_yaml
         <<~EOYAML
           deploy:
@@ -73,6 +102,15 @@ def deploy_spec_yaml
         EOYAML
       end
 
+      def deploy_spec_inherit_from_yaml
+        <<~EOYAML
+          inherit_from: shipit.yml
+          deploy:
+            override:
+              - test 11
+        EOYAML
+      end
+
       def deploy_spec_missing_deploy_yaml
         <<~EOYAML
           production_platform: