Build: Rework extra plugins support to be through sibling directories

This change removes the subdirectory support for extra-plugins, and
replaces it with an iteration of sibling directories with the prefix
"extra-plugin-".

TESTING.asciidoc

@@ -465,9 +465,10 @@ gradle run --debug-jvm
 == Building with extra plugins
 Additional plugins may be built alongside elasticsearch, where their
 dependency on elasticsearch will be substituted with the local elasticsearch
-build. To add your plugin, check it out into the extra-plugins directory.
-The build will automatically pick it up. You can verify the plugin is
-included as part of the build by checking the projects of the build.
+build. To add your plugin, check it out as a sibling directory of
+elasticsearch, with a prefix of "extra-plugin-". The build will automatically
+pick it up. You can verify the plugin is included as part of the build by
+checking the projects of the build.
 
 ---------------------------------------------------------------------------
 gradle projects

buildSrc/build.gradle

@@ -17,10 +17,19 @@
  * under the License.
  */
 
-plugins {
-  id 'groovy'
-  id 'com.bmuschko.nexus' version '2.3.1'
+// we must use buildscript + apply so that an external plugin
+// can apply this file, since the plugins directive is not
+// supported through file includes
+buildscript {
+  repositories {
+    jcenter()
   }
+  dependencies {
+    classpath 'com.bmuschko:gradle-nexus-plugin:2.3.1'
+  }
+}
+apply plugin: 'groovy'
+apply plugin: 'com.bmuschko.nexus'
 // TODO: move common IDE configuration to a common file to include
 apply plugin: 'idea'
 apply plugin: 'eclipse'

extra-plugins/build.gradle

@@ -1,10 +0,0 @@
-
-// This file exists solely for the purpose of allowing a nice error message
-// if someone tries running a gradle command from within the extra-plugins dir.
-
-println '''
-  Gradle commands are not supported from within the extra-plugins dir.
-  Please run your command either at the root of the elasticsearch checkout
-  or within a specific extra-plugins project.
-'''
-throw new GradleException('Cannot run commands in extra-plugins dir')

settings.gradle

@@ -61,19 +61,22 @@ if (isEclipse) {
   */
 void addSubProjects(String path, File dir) {
   if (dir.isDirectory() == false) return;
+  if (dir.name == 'buildSrc') return;
   if (new File(dir, 'build.gradle').exists() == false) return;
 
-  String projectName = "${path}:${dir.name}"
-  include projectName
-  project(projectName).projectDir = dir
+  include path
+  project(path).projectDir = dir
 
   for (File subdir : dir.listFiles()) {
-    addSubProjects(projectName, subdir)
+    addSubProjects("${path}:${subdir.name}", subdir)
   }
 }
 
-File extraPlugins = new File(rootProject.projectDir, 'extra-plugins')
-for (File extraPluginDir : extraPlugins.listFiles()) {
-  addSubProjects('', extraPluginDir)
+// look for sibling projects with the prefix "extra-plugin-"
+File siblings = rootProject.projectDir.parentFile
+for (File extraPluginDir : siblings.listFiles()) {
+  if (extraPluginDir.name.startsWith('extra-plugin-') == false) continue;
+  String path = ":${extraPluginDir.name.substring('extra-plugin-'.size())}"
+  addSubProjects(path, extraPluginDir)
 }