Set extra.plugin-optional composer flag (#217)

fixes #213

Author: nicolas-grekas

composer.json

@@ -48,7 +48,8 @@
         "test-ci": "vendor/bin/phpspec run -c phpspec.ci.yml"
     },
     "extra": {
-        "class": "Http\\Discovery\\Composer\\Plugin"
+        "class": "Http\\Discovery\\Composer\\Plugin",
+        "plugin-optional": true
     },
     "conflict": {
         "nyholm/psr7": "<1.0"

tests/install.sh

@@ -17,7 +17,8 @@ echo "Using directory: ${BUILD_DIR}"
 mkdir -p $BUILD_DIR
 
 # Init composer
-composer req --working-dir $BUILD_DIR php-http/discovery --no-update
+composer req --working-dir $BUILD_DIR php-http/discovery --no-update --no-plugins
+composer config --working-dir $BUILD_DIR --no-plugins allow-plugins.php-http/discovery false
 
 # Argument 3 installs additional composer packages
 composer req --working-dir $BUILD_DIR $3