enable Xdebug with docker build stage and dc override

Dockerfile

@@ -152,3 +152,12 @@ WORKDIR /srv/sylius
 
 COPY --from=sylius_php /srv/sylius/public public/
 COPY --from=sylius_nodejs /srv/sylius/public public/
+
+FROM symfony_php as sylius_php_dev
+
+ARG XDEBUG_VERSION=2.9.8
+RUN set -eux; \
+	apk add --no-cache --virtual .build-deps $PHPIZE_DEPS; \
+	pecl install xdebug-$XDEBUG_VERSION; \
+	docker-php-ext-enable xdebug; \
+	apk del .build-deps

docker-compose.debug.yaml

@@ -0,0 +1,19 @@
+version: "3.4"
+
+services:
+    php:
+        build:
+            context: .
+            target: sylius_php_dev
+        environment:
+            # See https://docs.docker.com/docker-for-mac/networking/#i-want-to-connect-from-a-container-to-a-service-on-the-host
+            # See https://github.com/docker/for-linux/issues/264
+            # The `remote_host` below may optionally be replaced with `remote_connect_back` (eg: linux users)
+            XDEBUG_CONFIG: >-
+                remote_enable=1
+                remote_host=host.docker.internal
+                remote_port=9001
+                idekey=PHPSTORM
+            # This should correspond to the server declared in PHPStorm `Preferences | Languages & Frameworks | PHP | Servers`
+            # Then PHPStorm will use the corresponding path mappings
+            PHP_IDE_CONFIG: serverName=sylius