Minimal Docker runtime (#998)

* Minimal Docker runtime

Allow contributors work on the code without actual PHP8 on their computers.

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

Co-authored-by: Tomas Votruba <tomas.vot@gmail.com>

.gitignore

@@ -18,3 +18,6 @@ box.phar
 php-parallel-lint
 
 tmp
+
+# Allow overrides for Docker configuration (custom volumes, env variables etc)
+docker-compose.override.yml

CONTRIBUTING.md

@@ -2,7 +2,20 @@
 
 Contributions here are more than welcomed! You can contribute to [rector-src](https://github.com/rectorphp/rector-src) repository.
 
-There 3 rules will highly increase changes to get your PR merged:
+### Preparing Local Environment
+
+If you have PHP 8 and Composer installed locally you can use it straight away. You can validate your environment with:
+
+```bash
+composer check-platform-reqs
+
+Alternatively you can use Docker runtime. All you need to do is wrap every command with `docker-compose run php`, so commands will be executed inside Docker container.
+
+For example `docker-compose run php composer install` will download PHP dependencies, so you can start using all scripts and work with the code.
+
+### Preparing Pull Request
+
+There 3 rules will highly increase chance to get your PR merged:
 
 - **1 feature per pull-request**
 - **new features need tests**

Dockerfile

@@ -0,0 +1,7 @@
+FROM php:8-cli-alpine
+
+WORKDIR /etc/rector
+
+COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
+
+RUN mkdir -p /etc/rector

docker-compose.yml

@@ -0,0 +1,7 @@
+version: "3.8"
+
+services:
+  php:
+    build: .
+    volumes:
+      - .:/etc/rector