Generate POM files with non-wildcard excludes (#21234)

Dependencies are currently marked as non-transitive in generated POM files by adding a wildcard (*) exclusion. This breaks compatibility with the dependency manager Apache Ivy as it incorrectly translates POMs with * excludes to Ivy XML with * excludes which results in the main artifact being excluded as well (see https://issues.apache.org/jira/browse/IVY-1531). To stay compatible with the current release of Ivy this commit uses explicit excludes for each transitive artifact instead to ensure that the main artifact is not excluded. This should be revisited when we upgrade Gradle to a higher version as the current one (2.13) as Gradle automatically translates non-transitive dependencies to * excludes in 2.14+.

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -28,6 +28,7 @@ import org.gradle.api.Task
 import org.gradle.api.XmlProvider
 import org.gradle.api.artifacts.Configuration
 import org.gradle.api.artifacts.ModuleDependency
+import org.gradle.api.artifacts.ModuleVersionIdentifier
 import org.gradle.api.artifacts.ProjectDependency
 import org.gradle.api.artifacts.ResolvedArtifact
 import org.gradle.api.artifacts.dsl.RepositoryHandler
@@ -294,12 +295,15 @@ class BuildPlugin implements Plugin<Project> {
      * Returns a closure which can be used with a MavenPom for fixing problems with gradle generated poms.
      *
      * <ul>
-     *     <li>Remove transitive dependencies (using wildcard exclusions, fixed in gradle 2.14)</li>
-     *     <li>Set compile time deps back to compile from runtime (known issue with maven-publish plugin)
+     *     <li>Remove transitive dependencies. We currently exclude all artifacts explicitly instead of using wildcards
+     *         as Ivy incorrectly translates POMs with * excludes to Ivy XML with * excludes which results in the main artifact
+     *         being excluded as well (see https://issues.apache.org/jira/browse/IVY-1531). Note that Gradle 2.14+ automatically
+     *         translates non-transitive dependencies to * excludes. We should revisit this when upgrading Gradle.</li>
+     *     <li>Set compile time deps back to compile from runtime (known issue with maven-publish plugin)</li>
      * </ul>
      */
     private static Closure fixupDependencies(Project project) {
-        // TODO: remove this when enforcing gradle 2.14+, it now properly handles exclusions
+        // TODO: revisit this when upgrading to Gradle 2.14+, see Javadoc comment above
         return { XmlProvider xml ->
             // first find if we have dependencies at all, and grab the node
             NodeList depsNodes = xml.asNode().get('dependencies')
@@ -334,10 +338,19 @@ class BuildPlugin implements Plugin<Project> {
                     continue
                 }
 
-                // we now know we have something to exclude, so add a wildcard exclusion element
-                Node exclusion = depNode.appendNode('exclusions').appendNode('exclusion')
-                exclusion.appendNode('groupId', '*')
-                exclusion.appendNode('artifactId', '*')
+                // we now know we have something to exclude, so add exclusions for all artifacts except the main one
+                Node exclusions = depNode.appendNode('exclusions')
+                for (ResolvedArtifact artifact : artifacts) {
+                    ModuleVersionIdentifier moduleVersionIdentifier = artifact.moduleVersion.id;
+                    String depGroupId = moduleVersionIdentifier.group
+                    String depArtifactId = moduleVersionIdentifier.name
+                    // add exclusions for all artifacts except the main one
+                    if (depGroupId != groupId || depArtifactId != artifactId) {
+                        Node exclusion = exclusions.appendNode('exclusion')
+                        exclusion.appendNode('groupId', depGroupId)
+                        exclusion.appendNode('artifactId', depArtifactId)
+                    }
+                }
             }
         }
     }