[FIXED JENKINS-8092]

Set M2_Home for maven builds and add maven to the path so if the build
needs to run maven from maven (or maven from ant from maven) it can.

changelog.html

@@ -72,6 +72,9 @@ Upcoming changes</a>
   <li class=rfe>
     Allow classworlds.conf to be externally configured for M3 builds
     (<a href="http://issues.jenkins-ci.org/browse/JENKINS-8905">issue 8905</a>)    
+  <li class=bug>
+    Configure the environment for Maven job type builds
+    (<a href="http://issues.jenkins-ci.org/browse/JENKINS-8092">issue 8902</a>)
 </ul>
 </div><!--=TRUNK-END=-->
 

maven-plugin/src/main/java/hudson/maven/MavenBuild.java

@@ -193,6 +193,18 @@ public class MavenBuild extends AbstractMavenBuild<MavenModule,MavenBuild> {
         String opts = project.getParent().getMavenOpts();
         if(opts!=null)
             envs.put("MAVEN_OPTS", opts);
+        // We need to add M2_HOME and the mvn binary to the PATH so if Maven
+        // needs to run Maven it will pick the correct one.
+        // This can happen if maven calls ANT which itself calls Maven
+        // or if Maven calls itself e.g. maven-release-plugin
+        MavenInstallation mvn = project.getParent().getMaven();
+        if (mvn == null)
+            throw new AbortException(
+                    "A Maven installation needs to be available for this project to be built.\n"
+                    + "Either your server has no Maven installations defined, or the requested Maven version does not exist.");
+        mvn = mvn.forEnvironment(envs).forNode(Computer.currentComputer().getNode(), log);
+        envs.put("M2_HOME", mvn.getHome());
+        envs.put("PATH+MAVEN", mvn.getHome() + "/bin");
         return envs;
     }
 

maven-plugin/src/main/java/hudson/maven/MavenModuleSetBuild.java

@@ -147,6 +147,20 @@ public class MavenModuleSetBuild extends AbstractMavenBuild<MavenModuleSet,Maven
         String opts = project.getMavenOpts();
         if(opts!=null)
             envs.put("MAVEN_OPTS", opts);
+        // We need to add M2_HOME and the mvn binary to the PATH so if Maven
+        // needs to run Maven it will pick the correct one.
+        // This can happen if maven calls ANT which itself calls Maven
+        // or if Maven calls itself e.g. maven-release-plugin
+        MavenInstallation mvn = project.getMaven();
+        if (mvn == null)
+            throw new AbortException(
+                    "A Maven installation needs to be available for this project to be built.\n"
+                    + "Either your server has no Maven installations defined, or the requested Maven version does not exist.");
+
+        mvn = mvn.forEnvironment(envs).forNode(
+                Computer.currentComputer().getNode(), log);
+        envs.put("M2_HOME", mvn.getHome());
+        envs.put("PATH+MAVEN", mvn.getHome() + "/bin");
         return envs;
     }