Use new wireCompatVersions property instead of bwcVersion (elastic/x-pack-elasticsearch#1466)

This is the xpack side of elastic/elasticsearch#24748

Original commit: elastic/x-pack-elasticsearch@8b7dd5cdbe

build.gradle

@@ -45,6 +45,6 @@ subprojects {
   }
   ext.projectSubstitutions += [
      "org.elasticsearch.plugin:x-pack-api:${version}": ':x-pack-elasticsearch:plugin',
-     "org.elasticsearch.plugin:x-pack:${bwcVersion}": ':x-pack-elasticsearch:plugin:bwc-zip'
+     "org.elasticsearch.plugin:x-pack:${wireCompatVersions[-1]}": ':x-pack-elasticsearch:plugin:bwc-zip'
   ]
 }

plugin/bwc-zip/build.gradle

@@ -3,14 +3,19 @@ import org.elasticsearch.gradle.LoggedExec
 
 /**
  * This is a dummy project which does a local checkout of the previous
- * major version's stable branch, and builds a snapshot. This allows backcompat
- * tests in the next major version to test against the next unreleased minor
- * version, without relying on snapshots.
+ * wire compat version's branch, and builds a snapshot. This allows backcompat
+ * tests to test against the next unreleased version, closest to this version,
+ * without relying on snapshots.
  */
 
+String bwcVersion = wireCompatVersions[-1]
+if (bwcVersion.endsWith('-SNAPSHOT')) {
   apply plugin: 'distribution'
 
-File esCheckoutDir = file("${buildDir}/bwc/checkout-es-5.x")
+  def (String major, String minor, String bugfix) = bwcVersion.split('\\.')
+  String bwcBranch = bugfix == '0-SNAPSHOT' ? "${major}.x" : "${major}.${minor}"
+
+  File esCheckoutDir = file("${buildDir}/bwc/checkout-es-${bwcBranch}")
   File xpackCheckoutDir = file("${esCheckoutDir}-extra/x-pack-elasticsearch")
   task createElasticsearchClone(type: LoggedExec) {
     onlyIf { esCheckoutDir.exists() == false }
@@ -94,13 +99,13 @@ task fetchXPackLatest(type: LoggedExec) {
   task checkoutElasticsearchBwcBranch(type: LoggedExec) {
     dependsOn fetchElasticsearchLatest
     workingDir = esCheckoutDir
-  commandLine = ['git', 'checkout', 'upstream/5.x']
+    commandLine = ['git', 'checkout', "upstream/${bwcBranch}"]
   }
 
   task checkoutXPackBwcBranch(type: LoggedExec) {
     dependsOn fetchXPackLatest
     workingDir = xpackCheckoutDir
-  commandLine = ['git', 'checkout', 'upstream/5.x']
+    commandLine = ['git', 'checkout', "upstream/${bwcBranch}"]
   }
 
   File bwcZip = file("${xpackCheckoutDir}/plugin/build/distributions/x-pack-${bwcVersion}.zip")
@@ -113,4 +118,4 @@ task buildBwcVersion(type: GradleBuild) {
   artifacts {
     'default' file: bwcZip, name: 'x-pack', type: 'zip', builtBy: buildBwcVersion
   }
-
+}

qa/rolling-upgrade/build.gradle

@@ -56,7 +56,7 @@ task oldClusterTest(type: RestIntegTestTask) {
 oldClusterTestCluster {
     plugin ':x-pack-elasticsearch:plugin'
     distribution = 'zip'
-    bwcVersion = project.bwcVersion // TODO: either randomize, or make this settable with sysprop
+    bwcVersion = project.wireCompatVersions[-1] // TODO: either randomize, or make this settable with sysprop
     numBwcNodes = 2
     numNodes = 2
     clusterName = 'rolling-upgrade'