Add projections file

.gitignore

@@ -81,3 +81,4 @@ package-lock.json
 jsdoc/
 **/tmp/rubocop_cache/**
 .overcommit.yml
+.projections.json

.projections.json.example

+{
+  "app/*.rb": {
+    "alternate": "spec/{}_spec.rb",
+    "type": "source"
+  },
+  "spec/*_spec.rb": {
+    "alternate": "app/{}.rb",
+    "type": "test"
+  },
+  "lib/*.rb": {
+    "alternate": "spec/lib/{}_spec.rb",
+    "type": "source"
+  },
+  "spec/lib/*_spec.rb": {
+    "alternate": "lib/{}.rb",
+    "type": "test"
+  },
+  "ee/app/*.rb": {
+    "alternate": "ee/spec/{}_spec.rb",
+    "type": "source"
+  },
+  "ee/spec/*_spec.rb": {
+    "alternate": "ee/app/{}.rb",
+    "type": "test"
+  },
+  "ee/lib/*.rb": {
+    "alternate": "ee/spec/lib/{}_spec.rb",
+    "type": "source"
+  },
+  "ee/spec/lib/*_spec.rb": {
+    "alternate": "ee/lib/{}.rb",
+    "type": "test"
+  },
+  "*.rb": {"dispatch": "bundle exec rubocop {file}"},
+  "*_spec.rb": {"dispatch": "bundle exec rspec {file}"}
+}

doc/development/README.md

@@ -165,6 +165,10 @@ description: 'Learn how to contribute to GitLab.'
 
 - [Shell scripting standards and style guidelines](shell_scripting_guide/index.md)
 
+## Other Development guides
+
+- [Defining relations between files using projections](projections.md)
+
 ## Other GitLab Development Kit (GDK) guides
 
 - [Run full Auto DevOps cycle in a GDK instance](https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/howto/auto_devops.md)

doc/development/projections.md

+# Projections
+
+Projections are a way to define relations between files. Every file can have a
+"related" or "alternate" file. It's common to consider spec files to be
+"alternate" files to source files.
+
+## How to use it
+
+- Install an editor plugin that consumes projections
+- Copy `.projections.json.example` to `.projections.json`
+
+## How to customize it
+
+You can find a basic list of projection options in
+[projectionist.txt](https://github.com/tpope/vim-projectionist/blob/master/doc/projectionist.txt)
+
+## Which plugins can I use
+
+- vim
+  - [vim-projectionist](https://github.com/tpope/vim-projectionist)
+- VSCode
+  - [Alternate File](https://marketplace.visualstudio.com/items?itemName=will-wow.vscode-alternate-file)
+  - [projectionist](https://github.com/jarsen/projectionist)
+  - [jumpto](https://github.com/gmdayley/jumpto)
+- Atom
+  - [projectionist-atom](https://atom.io/packages/projectionist-atom)
+- Command-line
+  - [projectionist](https://github.com/glittershark/projectionist)
+
+## History
+
+This started as a
+[plugin for vim by tpope](https://github.com/tpope/vim-projectionist)
+It has since become editor-agnostic and ported to most modern editors.