[SPARK-15827][BUILD] Publish Spark's forked sbt-pom-reader to Maven Central

Spark's SBT build currently uses a fork of the sbt-pom-reader plugin but depends on that fork via a SBT subproject which is cloned from https://github.com/scrapcodes/sbt-pom-reader/tree/ignore_artifact_id. This unnecessarily slows down the initial build on fresh machines and is also risky because it risks a build breakage in case that GitHub repository ever changes or is deleted.

In order to address these issues, I have published a pre-built binary of our forked sbt-pom-reader plugin to Maven Central under the `org.spark-project` namespace and have updated Spark's build to use that artifact. This published artifact was built from https://github.com/JoshRosen/sbt-pom-reader/tree/v1.0.0-spark, which contains the contents of ScrapCodes's branch plus an additional patch to configure the build for artifact publication.

/cc srowen ScrapCodes for review.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #13564 from JoshRosen/use-published-fork-of-pom-reader.

project/plugins.sbt

@@ -21,3 +21,12 @@ libraryDependencies += "org.ow2.asm"  % "asm" % "5.0.3"
 libraryDependencies += "org.ow2.asm"  % "asm-commons" % "5.0.3"
 
 addSbtPlugin("com.simplytyped" % "sbt-antlr4" % "0.7.11")
+
+// Spark uses a custom fork of the sbt-pom-reader plugin which contains a patch to fix issues
+// related to test-jar dependencies (https://github.com/sbt/sbt-pom-reader/pull/14). The source for
+// this fork is published at https://github.com/JoshRosen/sbt-pom-reader/tree/v1.0.0-spark
+// and corresponds to commit b160317fcb0b9d1009635a7c5aa05d0f3be61936 in that repository.
+// In the long run, we should try to merge our patch upstream and switch to an upstream version of
+// the plugin; this is tracked at SPARK-14401.
+
+addSbtPlugin("org.spark-project" % "sbt-pom-reader" % "1.0.0-spark")

project/project/SparkPluginBuild.scala

-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-import sbt._
-import sbt.Keys._
-
-/**
- * This plugin project is there because we use our custom fork of sbt-pom-reader plugin. This is
- * a plugin project so that this gets compiled first and is available on the classpath for SBT build.
- */
-object SparkPluginDef extends Build {
-  lazy val root = Project("plugins", file(".")) dependsOn(sbtPomReader)
-  lazy val sbtPomReader = uri("https://github.com/ScrapCodes/sbt-pom-reader.git#ignore_artifact_id")
-}