Rework bwc snapshot projects to build up to two bwc versions

build.gradle

@@ -218,12 +218,22 @@ subprojects {
     "org.elasticsearch.plugin:aggs-matrix-stats-client:${version}": ':modules:aggs-matrix-stats',
     "org.elasticsearch.plugin:percolator-client:${version}": ':modules:percolator',
   ]
-  if (wireCompatVersions[-1].snapshot) {
-    // if the most previous version is a snapshot, we need to connect that version to the
-    // bwc project which will checkout and build that snapshot version
-    ext.projectSubstitutions["org.elasticsearch.distribution.deb:elasticsearch:${wireCompatVersions[-1]}"] = ':distribution:bwc'
-    ext.projectSubstitutions["org.elasticsearch.distribution.rpm:elasticsearch:${wireCompatVersions[-1]}"] = ':distribution:bwc'
-    ext.projectSubstitutions["org.elasticsearch.distribution.zip:elasticsearch:${wireCompatVersions[-1]}"] = ':distribution:bwc'
+  if (indexCompatVersions[-1].snapshot) {
+    /* The last and second to last versions can be snapshots. Rather than use
+     * snapshots built by CI we connect these versions to projects that build
+     * those those versions from the HEAD of the appropriate branch. */
+    if (indexCompatVersions[-1].bugfix == 0) {
+      ext.projectSubstitutions["org.elasticsearch.distribution.deb:elasticsearch:${indexCompatVersions[-1]}"] = ':distribution:bwc-stable-snapshot'
+      ext.projectSubstitutions["org.elasticsearch.distribution.rpm:elasticsearch:${indexCompatVersions[-1]}"] = ':distribution:bwc-stable-snapshot'
+      ext.projectSubstitutions["org.elasticsearch.distribution.zip:elasticsearch:${indexCompatVersions[-1]}"] = ':distribution:bwc-stable-snapshot'
+      ext.projectSubstitutions["org.elasticsearch.distribution.deb:elasticsearch:${indexCompatVersions[-2]}"] = ':distribution:bwc-release-snapshot'
+      ext.projectSubstitutions["org.elasticsearch.distribution.rpm:elasticsearch:${indexCompatVersions[-2]}"] = ':distribution:bwc-release-snapshot'
+      ext.projectSubstitutions["org.elasticsearch.distribution.zip:elasticsearch:${indexCompatVersions[-2]}"] = ':distribution:bwc-release-snapshot'
+    } else {
+      ext.projectSubstitutions["org.elasticsearch.distribution.deb:elasticsearch:${indexCompatVersions[-1]}"] = ':distribution:bwc-release-snapshot'
+      ext.projectSubstitutions["org.elasticsearch.distribution.rpm:elasticsearch:${indexCompatVersions[-1]}"] = ':distribution:bwc-release-snapshot'
+      ext.projectSubstitutions["org.elasticsearch.distribution.zip:elasticsearch:${indexCompatVersions[-1]}"] = ':distribution:bwc-release-snapshot'
+    }
   }
   project.afterEvaluate {
     configurations.all {

distribution/build.gradle

@@ -41,7 +41,7 @@ buildscript {
 }
 
 Collection distributions = project.subprojects.findAll {
-   it.path.contains(':tools') == false && it.name != 'bwc' }
+   it.path.contains(':tools') == false && it.path.contains(':bwc') == false }
 
 /*****************************************************************************
  *                                Notice file                                *

distribution/bwc/build.gradle

@@ -26,14 +26,35 @@ import org.elasticsearch.gradle.LoggedExec
  * tests to test against the next unreleased version, closest to this version,
  * without relying on snapshots.
  */
+String bwcVersion
+boolean enabled = true
+if (project.name == 'bwc-stable-snapshot') {
+  /* bwc-stable is only used if the last version is on a stable branch instead
+   * of a bugfix branch */
+  enabled = indexCompatVersions[-1].bugfix == 0
+  bwcVersion = indexCompatVersions[-1]
+} else if (project.name == 'bwc-release-snapshot') {
+  if (indexCompatVersions[-1].bugfix == 0) {
+    /* The last version is on a stable branch so it is handled by the bwc-stable
+     * project. This project will instead handle the version before that which
+     * *should* be on a stable branch. */
+    bwcVersion = indexCompatVersions[-2]
+  } else {
+    // The last version is on a release branch so it is handled by this project
+    bwcVersion = indexCompatVersions[-1]
+  }
+} else {
+  throw new InvalidUserDataException("Unsupport project name ${project.name}")
+}
 
-String bwcVersion = wireCompatVersions[-1]
-if (bwcVersion.endsWith('-SNAPSHOT')) {
+if (enabled) {
   apply plugin: 'distribution'
 
   def (String major, String minor, String bugfix) = bwcVersion.split('\\.')
-  String bwcBranch = bugfix == '0-SNAPSHOT' ? "${major}.x" : "${major}.${minor}"
+  String bwcBranch =
+      project.name == 'bwc-stable-snapshot' ? "${major}.x" : "${major}.${minor}"
   File checkoutDir = file("${buildDir}/bwc/checkout-${bwcBranch}")
+
   task createClone(type: LoggedExec) {
     onlyIf { checkoutDir.exists() == false }
     commandLine = ['git', 'clone', rootDir, checkoutDir]

settings.gradle

@@ -15,7 +15,8 @@ List projects = [
   'client:benchmark',
   'benchmarks',
   'distribution:integ-test-zip',
-  'distribution:bwc',
+  'distribution:bwc-release-snapshot',
+  'distribution:bwc-stable-snapshot',
   'distribution:zip',
   'distribution:tar',
   'distribution:deb',
@@ -106,6 +107,13 @@ for (String example : examplePlugins) {
   project(":example-plugins:${example}").projectDir = new File(rootProject.projectDir, "plugins/examples/${example}")
 }
 
+/* bwc and bwc-unreleased share the same build directory and build file, but
+ * apply to different backwards compatibility branches. */
+project(':distribution:bwc-release-snapshot').projectDir =
+    new File(rootProject.projectDir, 'distribution/bwc')
+project(':distribution:bwc-stable-snapshot').projectDir =
+    new File(rootProject.projectDir, 'distribution/bwc')
+
 if (isEclipse) {
   project(":core").projectDir = new File(rootProject.projectDir, 'core/src/main')
   project(":core").buildFileName = 'eclipse-build.gradle'