Consolidate version numbering semantics (#27397)

Fixes to the build system, particularly around BWC testing, and to make future
version bumps less painful.

build.gradle

@@ -17,15 +17,15 @@
  * under the License.
  */
 
-import java.nio.file.Path
-import java.util.regex.Matcher
-import org.eclipse.jgit.lib.Repository
-import org.eclipse.jgit.lib.RepositoryBuilder
-import org.gradle.plugins.ide.eclipse.model.SourceFolder
+
 import org.apache.tools.ant.taskdefs.condition.Os
 import org.elasticsearch.gradle.BuildPlugin
-import org.elasticsearch.gradle.VersionProperties
 import org.elasticsearch.gradle.Version
+import org.elasticsearch.gradle.VersionCollection
+import org.elasticsearch.gradle.VersionProperties
+import org.gradle.plugins.ide.eclipse.model.SourceFolder
+
+import java.nio.file.Path
 
 // common maven publishing configuration
 subprojects {
@@ -67,72 +67,16 @@ configure(subprojects.findAll { it.projectDir.toPath().startsWith(rootPath) }) {
   }
 }
 
-/* Introspect all versions of ES that may be tested agains for backwards
+/* Introspect all versions of ES that may be tested against for backwards
  * compatibility. It is *super* important that this logic is the same as the
  * logic in VersionUtils.java, throwing out alphas because they don't have any
  * backwards compatibility guarantees and only keeping the latest beta or rc
  * in a branch if there are only betas and rcs in the branch so we have
  * *something* to test against. */
-Version currentVersion = Version.fromString(VersionProperties.elasticsearch.minus('-SNAPSHOT'))
-int prevMajor = currentVersion.major - 1
-File versionFile = file('core/src/main/java/org/elasticsearch/Version.java')
-List<String> versionLines = versionFile.readLines('UTF-8')
-List<Version> versions = []
-// keep track of the previous major version's last minor, so we know where wire compat begins
-int prevMinorIndex = -1 // index in the versions list of the last minor from the prev major
-int lastPrevMinor = -1 // the minor version number from the prev major we most recently seen
-int prevBugfixIndex = -1 // index in the versions list of the last bugfix release from the prev major
-for (String line : versionLines) {
-  /* Note that this skips alphas and betas which is fine because they aren't
-   * compatible with anything. */
-  Matcher match = line =~ /\W+public static final Version V_(\d+)_(\d+)_(\d+)(_beta\d+|_rc\d+)? .*/
-  if (match.matches()) {
-    int major = Integer.parseInt(match.group(1))
-    int minor = Integer.parseInt(match.group(2))
-    int bugfix = Integer.parseInt(match.group(3))
-    String suffix = (match.group(4) ?: '').replace('_', '-')
-    Version foundVersion = new Version(major, minor, bugfix, suffix, false)
-    if (currentVersion != foundVersion
-        && (major == prevMajor || major == currentVersion.major)) {
-      if (versions.isEmpty() || versions.last() != foundVersion) {
-        versions.add(foundVersion)
-      } else {
-        // Replace the earlier betas with later ones
-        Version last = versions.set(versions.size() - 1, foundVersion)
-        if (last.suffix == '') {
-          throw new InvalidUserDataException("Found two equal versions but"
-              + " the first one [$last] wasn't a beta.")
-        }
-      }
-      if (major == prevMajor && minor > lastPrevMinor) {
-        prevMinorIndex = versions.size() - 1
-        lastPrevMinor = minor
-      }
-    }
-    if (major == prevMajor) {
-      prevBugfixIndex = versions.size() - 1
-    }
-  }
-}
-if (versions.toSorted { it.id } != versions) {
-  println "Versions: ${versions}"
-  throw new GradleException("Versions.java contains out of order version constants")
-}
-if (prevBugfixIndex != -1) {
-  versions[prevBugfixIndex] = new Version(versions[prevBugfixIndex].major, versions[prevBugfixIndex].minor,
-                                          versions[prevBugfixIndex].bugfix, versions[prevBugfixIndex].suffix, true)
-}
-if (currentVersion.bugfix == 0) {
-  // If on a release branch, after the initial release of that branch, the bugfix version will
-  // be bumped, and will be != 0. On master and N.x branches, we want to test against the
-  // unreleased version of closest branch. So for those cases, the version includes -SNAPSHOT,
-  // and the bwc distribution will checkout and build that version.
-  Version last = versions[-1]
-  versions[-1] = new Version(last.major, last.minor, last.bugfix, last.suffix, true)
-  if (last.bugfix == 0) {
-    versions[-2] = new Version(
-        versions[-2].major, versions[-2].minor, versions[-2].bugfix, versions[-2].suffix, true)
-  }
+VersionCollection versions = new VersionCollection(file('core/src/main/java/org/elasticsearch/Version.java').readLines('UTF-8'))
+if (versions.currentVersion.toString() != VersionProperties.elasticsearch) {
+  throw new GradleException("The last version in Versions.java [${versions.currentVersion}] does not match " +
+          "VersionProperties.elasticsearch [${VersionProperties.elasticsearch}]")
 }
 
 // build metadata from previous build, contains eg hashes for bwc builds
@@ -151,9 +95,10 @@ allprojects {
     // for ide hacks...
     isEclipse = System.getProperty("eclipse.launcher") != null || gradle.startParameter.taskNames.contains('eclipse') || gradle.startParameter.taskNames.contains('cleanEclipse')
     isIdea = System.getProperty("idea.active") != null || gradle.startParameter.taskNames.contains('idea') || gradle.startParameter.taskNames.contains('cleanIdea')
-    // for backcompat testing
-    indexCompatVersions = versions
-    wireCompatVersions = versions.subList(prevMinorIndex, versions.size())
+
+    // for BWC testing
+    versionCollection = versions
+
     buildMetadata = buildMetadataMap
   }
 }
@@ -171,13 +116,13 @@ task verifyVersions {
     Set<Version> knownVersions = new TreeSet<>(xml.versioning.versions.version.collect { it.text() }.findAll { it ==~ /\d\.\d\.\d/ }.collect { Version.fromString(it) })
 
     // Limit the known versions to those that should be index compatible, and are not future versions
-    knownVersions = knownVersions.findAll { it.major >= prevMajor && it.before(VersionProperties.elasticsearch) }
+    knownVersions = knownVersions.findAll { it.major >= versions.currentVersion.major - 1 && it.before(VersionProperties.elasticsearch) }
 
     /* Limit the listed versions to those that have been marked as released.
      * Versions not marked as released don't get the same testing and we want
      * to make sure that we flip all unreleased versions to released as soon
      * as possible after release. */
-    Set<Version> actualVersions = new TreeSet<>(indexCompatVersions.findAll { false == it.snapshot })
+    Set<Version> actualVersions = new TreeSet<>(versions.versionsIndexCompatibleWithCurrent.findAll { false == it.snapshot })
 
     // Finally, compare!
     if (knownVersions.equals(actualVersions) == false) {
@@ -252,30 +197,17 @@ subprojects {
     "org.elasticsearch.plugin:aggs-matrix-stats-client:${version}": ':modules:aggs-matrix-stats',
     "org.elasticsearch.plugin:percolator-client:${version}": ':modules:percolator',
   ]
-  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:${indexCompatVersions[-1]}"] = ':distribution:bwc-stable-snapshot'
-      if (indexCompatVersions.size() > 1) {
-        ext.projectSubstitutions["org.elasticsearch.distribution.deb:elasticsearch:${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:${indexCompatVersions[-1]}"] = ':distribution:bwc-release-snapshot'
+
+  for (final Version version : versionCollection.versionsIndexCompatibleWithCurrent) {
+    if (version.branch != null) {
+      final String snapshotProject = ":distribution:bwc-snapshot-${version.branch}"
+      project(snapshotProject).ext.bwcVersion = version
+      ext.projectSubstitutions["org.elasticsearch.distribution.deb:elasticsearch:${version}"] = snapshotProject
+      ext.projectSubstitutions["org.elasticsearch.distribution.rpm:elasticsearch:${version}"] = snapshotProject
+      ext.projectSubstitutions["org.elasticsearch.distribution.zip:elasticsearch:${version}"] = snapshotProject
     }
-  } else if (indexCompatVersions[-2].snapshot) {
-    /* This is a terrible hack for the bump to 6.0.1 which will be fixed by #27397 */
-    ext.projectSubstitutions["org.elasticsearch.distribution.deb:elasticsearch:${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'
   }
+
   project.afterEvaluate {
     configurations.all {
       resolutionStrategy.dependencySubstitution { DependencySubstitutions subs ->

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

@@ -31,9 +31,10 @@ public class Version {
 
     final int major
     final int minor
-    final int bugfix
+    final int revision
     final int id
     final boolean snapshot
+    final String branch
     /**
      * Suffix on the version name. Unlike Version.java the build does not
      * consider alphas and betas different versions, it just preserves the
@@ -41,14 +42,15 @@ public class Version {
      */
     final String suffix
 
-    public Version(int major, int minor, int bugfix,
-            String suffix, boolean snapshot) {
+    public Version(int major, int minor, int revision,
+            String suffix, boolean snapshot, String branch) {
         this.major = major
         this.minor = minor
-        this.bugfix = bugfix
+        this.revision = revision
         this.snapshot = snapshot
         this.suffix = suffix
-        this.id = major * 100000 + minor * 1000 + bugfix * 10 +
+        this.branch = branch
+        this.id = major * 100000 + minor * 1000 + revision * 10 +
             (snapshot ? 1 : 0)
     }
 
@@ -58,13 +60,13 @@ public class Version {
             throw new InvalidUserDataException("Invalid version [${s}]")
         }
         return new Version(m.group(1) as int, m.group(2) as int,
-            m.group(3) as int, m.group(4) ?: '', m.group(5) != null)
+            m.group(3) as int, m.group(4) ?: '', m.group(5) != null, null)
     }
 
     @Override
     public String toString() {
         String snapshotStr = snapshot ? '-SNAPSHOT' : ''
-        return "${major}.${minor}.${bugfix}${suffix}${snapshotStr}"
+        return "${major}.${minor}.${revision}${suffix}${snapshotStr}"
     }
 
     public boolean before(String compareTo) {
@@ -82,4 +84,43 @@ public class Version {
     public boolean after(String compareTo) {
         return id > fromString(compareTo).id
     }
+
+    public boolean onOrBeforeIncludingSuffix(Version otherVersion) {
+        if (id != otherVersion.id) {
+            return id < otherVersion.id
+        }
+
+        if (suffix == '') {
+            return otherVersion.suffix == ''
+        }
+
+        return otherVersion.suffix == '' || suffix < otherVersion.suffix
+    }
+
+    boolean equals(o) {
+        if (this.is(o)) return true
+        if (getClass() != o.class) return false
+
+        Version version = (Version) o
+
+        if (id != version.id) return false
+        if (major != version.major) return false
+        if (minor != version.minor) return false
+        if (revision != version.revision) return false
+        if (snapshot != version.snapshot) return false
+        if (suffix != version.suffix) return false
+
+        return true
+    }
+
+    int hashCode() {
+        int result
+        result = major
+        result = 31 * result + minor
+        result = 31 * result + revision
+        result = 31 * result + id
+        result = 31 * result + (snapshot ? 1 : 0)
+        result = 31 * result + (suffix != null ? suffix.hashCode() : 0)
+        return result
+    }
 }

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

@@ -0,0 +1,193 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch 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.
+ */
+
+package org.elasticsearch.gradle
+
+import org.gradle.api.GradleException
+
+import java.util.regex.Matcher
+
+/**
+ * The collection of version constants declared in Version.java, for use in BWC testing.
+ */
+class VersionCollection {
+
+    private final List<Version> versions
+
+    /**
+     * Construct a VersionCollection from the lines of the Version.java file.
+     * @param versionLines The lines of the Version.java file.
+     */
+    VersionCollection(List<String> versionLines) {
+
+        List<Version> versions = []
+
+        for (final String line : versionLines) {
+            final Matcher match = line =~ /\W+public static final Version V_(\d+)_(\d+)_(\d+)(_alpha\d+|_beta\d+|_rc\d+)? .*/
+            if (match.matches()) {
+                final Version foundVersion = new Version(
+                        Integer.parseInt(match.group(1)), Integer.parseInt(match.group(2)),
+                        Integer.parseInt(match.group(3)), (match.group(4) ?: '').replace('_', '-'), false, null)
+
+                if (versions.size() > 0 && foundVersion.onOrBeforeIncludingSuffix(versions[-1])) {
+                    throw new GradleException("Versions.java contains out of order version constants:" +
+                            " ${foundVersion} should come before ${versions[-1]}")
+                }
+
+                // Only keep the last alpha/beta/rc in the series
+                if (versions.size() > 0 && versions[-1].id == foundVersion.id) {
+                    versions[-1] = foundVersion
+                } else {
+                    versions.add(foundVersion)
+                }
+            }
+        }
+
+        if (versions.empty) {
+            throw new GradleException("Unexpectedly found no version constants in Versions.java");
+        }
+
+        // The tip of each minor series (>= 5.6) is unreleased, so set their 'snapshot' flags
+        Version prevConsideredVersion = null
+        boolean found6xSnapshot = false
+        for (final int versionIndex = versions.size() - 1; versionIndex >= 0; versionIndex--) {
+            final Version currConsideredVersion = versions[versionIndex]
+
+            if (prevConsideredVersion == null
+                    || currConsideredVersion.major != prevConsideredVersion.major
+                    || currConsideredVersion.minor != prevConsideredVersion.minor) {
+
+                // This is a snapshot version. Work out its branch. NB this doesn't name the current branch correctly, but this doesn't
+                // matter as we don't BWC test against it.
+                String branch = "${currConsideredVersion.major}.${currConsideredVersion.minor}"
+
+                if (false == found6xSnapshot && currConsideredVersion.major == 6) {
+                    // TODO needs generalising to deal with when 7.x is cut, and when 6.x is deleted, and so on...
+                    branch = "6.x"
+                    found6xSnapshot = true
+                }
+
+                versions[versionIndex] = new Version(
+                        currConsideredVersion.major, currConsideredVersion.minor,
+                        currConsideredVersion.revision, currConsideredVersion.suffix, true, branch)
+            }
+
+            if (currConsideredVersion.onOrBefore("5.6.0")) {
+                break
+            }
+
+            prevConsideredVersion = currConsideredVersion
+        }
+
+        this.versions = Collections.unmodifiableList(versions)
+    }
+
+    /**
+     * @return The list of versions read from the Version.java file
+     */
+    List<Version> getVersions() {
+        return Collections.unmodifiableList(versions)
+    }
+
+    /**
+     * @return The latest version in the Version.java file, which must be the current version of the system.
+     */
+    Version getCurrentVersion() {
+        return versions[-1]
+    }
+
+    /**
+     * @return The snapshot at the end of the previous minor series in the current major series, or null if this is the first minor series.
+     */
+    Version getBWCSnapshotForCurrentMajor() {
+        return getLastSnapshotWithMajor(currentVersion.major)
+    }
+
+    /**
+     * @return The snapshot at the end of the previous major series, which must not be null.
+     */
+    Version getBWCSnapshotForPreviousMajor() {
+        Version version = getLastSnapshotWithMajor(currentVersion.major - 1)
+        assert version != null : "getBWCSnapshotForPreviousMajor(): found no versions in the previous major"
+        return version
+    }
+
+    /**
+     * @return The snapshot at the end of the previous-but-one minor series in the current major series, if the previous minor series
+     * exists and has not yet been released. Otherwise null.
+     */
+    Version getBWCSnapshotForPreviousMinorOfCurrentMajor() {
+        // If we are at 6.2.0 but 6.1.0 has not yet been released then we
+        // need to test against 6.0.1-SNAPSHOT too
+        final Version v = BWCSnapshotForCurrentMajor
+        if (v == null || v.revision != 0 || v.minor == 0) {
+            return null
+        }
+        return versions.find { it.major == v.major && it.minor == v.minor - 1 && it.snapshot }
+    }
+
+    private Version getLastSnapshotWithMajor(int targetMajor) {
+        final String currentVersion = currentVersion.toString()
+        final int snapshotIndex = versions.findLastIndexOf {
+            it.major == targetMajor && it.before(currentVersion) && it.snapshot
+        }
+        return snapshotIndex == -1 ? null : versions[snapshotIndex]
+    }
+
+    private List<Version> versionsOnOrAfterExceptCurrent(Version minVersion) {
+        final String minVersionString = minVersion.toString()
+        return Collections.unmodifiableList(versions.findAll {
+            it.onOrAfter(minVersionString) && it != currentVersion
+        })
+    }
+
+    /**
+     * @return All earlier versions that should be tested for index BWC with the current version.
+     */
+    List<Version> getVersionsIndexCompatibleWithCurrent() {
+        final Version firstVersionOfCurrentMajor = versions.find { it.major >= currentVersion.major - 1 }
+        return versionsOnOrAfterExceptCurrent(firstVersionOfCurrentMajor)
+    }
+
+    private Version getMinimumWireCompatibilityVersion() {
+        final int firstIndexOfThisMajor = versions.findIndexOf { it.major == currentVersion.major }
+        if (firstIndexOfThisMajor == 0) {
+            return versions[0]
+        }
+        final Version lastVersionOfEarlierMajor = versions[firstIndexOfThisMajor - 1]
+        return versions.find { it.major == lastVersionOfEarlierMajor.major && it.minor == lastVersionOfEarlierMajor.minor }
+    }
+
+    /**
+     * @return All earlier versions that should be tested for wire BWC with the current version.
+     */
+    List<Version> getVersionsWireCompatibleWithCurrent() {
+        return versionsOnOrAfterExceptCurrent(minimumWireCompatibilityVersion)
+    }
+
+    /**
+     * `gradle check` does not run all BWC tests. This defines which tests it does run.
+     * @return Versions to test for BWC during gradle check.
+     */
+    List<Version> getBasicIntegrationTestVersions() {
+        // TODO these are the versions checked by `gradle check` for BWC tests. Their choice seems a litle arbitrary.
+        List<Version> result = [BWCSnapshotForPreviousMajor, BWCSnapshotForCurrentMajor]
+        return Collections.unmodifiableList(result.findAll { it != null })
+    }
+}

buildSrc/src/main/groovy/org/elasticsearch/gradle/vagrant/VagrantTestPlugin.groovy

@@ -107,7 +107,8 @@ class VagrantTestPlugin implements Plugin<Project> {
         if (upgradeFromVersion == null) {
             String firstPartOfSeed = project.rootProject.testSeed.tokenize(':').get(0)
             final long seed = Long.parseUnsignedLong(firstPartOfSeed, 16)
-            upgradeFromVersion = project.indexCompatVersions[new Random(seed).nextInt(project.indexCompatVersions.size())]
+            final def indexCompatVersions = project.versionCollection.versionsIndexCompatibleWithCurrent
+            upgradeFromVersion = indexCompatVersions[new Random(seed).nextInt(indexCompatVersions.size())]
         }
 
         DISTRIBUTION_ARCHIVES.each {

distribution/bwc/build.gradle

@@ -19,6 +19,8 @@
 
 
 import org.elasticsearch.gradle.LoggedExec
+import org.elasticsearch.gradle.Version
+import java.util.regex.Matcher
 
 /**
  * This is a dummy project which does a local checkout of the previous
@@ -26,41 +28,20 @@ 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 {
+final Matcher match = project.name =~ /bwc-snapshot-(\d+\.(\d+|x))/
+if (!match.matches()) {
   throw new InvalidUserDataException("Unsupport project name ${project.name}")
 }
+String bwcBranch = match.group(1)
+
+if (project.hasProperty('bwcVersion')) {
+  Version bwcVersion = project.ext.bwcVersion
 
-if (enabled) {
   apply plugin: 'distribution'
   // Not published so no need to assemble
   tasks.remove(assemble)
   build.dependsOn.remove('assemble')
 
-  def (String major, String minor, String bugfix) = bwcVersion.split('\\.')
-  def (String currentMajor, String currentMinor, String currentBugfix) = version.split('\\.')
-  String bwcBranch
-  if (project.name == 'bwc-stable-snapshot' && major != currentMajor) {
-    bwcBranch = "${major}.x"
-  } else {
-    bwcBranch = "${major}.${minor}"
-  }
   File checkoutDir = file("${buildDir}/bwc/checkout-${bwcBranch}")
 
   final String remote = System.getProperty("tests.bwc.remote", "elastic")

qa/full-cluster-restart/build.gradle

@@ -17,8 +17,9 @@
  * under the License.
  */
 
-import org.elasticsearch.gradle.test.RestIntegTestTask
+
 import org.elasticsearch.gradle.Version
+import org.elasticsearch.gradle.test.RestIntegTestTask
 
 apply plugin: 'elasticsearch.standalone-test'
 
@@ -29,7 +30,7 @@ task bwcTest {
   group = 'verification'
 }
 
-for (Version version : indexCompatVersions) {
+for (Version version : versionCollection.versionsIndexCompatibleWithCurrent) {
   String baseName = "v${version}"
 
   Task oldClusterTest = tasks.create(name: "${baseName}#oldClusterTest", type: RestIntegTestTask) {
@@ -104,9 +105,8 @@ test.enabled = false // no unit tests for rolling upgrades, only the rest integr
 // basic integ tests includes testing bwc against the most recent version
 task integTest {
   if (project.bwc_tests_enabled) {
-    dependsOn "v${indexCompatVersions[-1]}#bwcTest"
-    if (indexCompatVersions[-1].bugfix == 0) {
-      dependsOn "v${indexCompatVersions[-2]}#bwcTest"
+    for (final def version : versionCollection.basicIntegrationTestVersions) {
+      dependsOn "v${version}#bwcTest"
     }
   }
 }

qa/mixed-cluster/build.gradle

@@ -29,7 +29,7 @@ task bwcTest {
   group = 'verification'
 }
 
-for (Version version : wireCompatVersions) {
+for (Version version : versionCollection.versionsWireCompatibleWithCurrent) {
   String baseName = "v${version}"
 
   Task mixedClusterTest = tasks.create(name: "${baseName}#mixedClusterTest", type: RestIntegTestTask) {
@@ -68,8 +68,8 @@ test.enabled = false // no unit tests for rolling upgrades, only the rest integr
 
 // basic integ tests includes testing bwc against the most recent version
 task integTest {
-  if (project.bwc_tests_enabled) {
-    dependsOn = ["v${wireCompatVersions[-1]}#bwcTest"]
+  for (final def version : versionCollection.basicIntegrationTestVersions) {
+    dependsOn "v${version}#bwcTest"
   }
 }
 

qa/query-builder-bwc/build.gradle

@@ -30,7 +30,7 @@ task bwcTest {
     group = 'verification'
 }
 
-for (Version version : indexCompatVersions) {
+for (Version version : versionCollection.versionsIndexCompatibleWithCurrent) {
     String baseName = "v${version}"
 
     Task oldQueryBuilderTest = tasks.create(name: "${baseName}#oldQueryBuilderTest", type: RestIntegTestTask) {
@@ -83,7 +83,9 @@ test.enabled = false // no unit tests for rolling upgrades, only the rest integr
 // basic integ tests includes testing bwc against the most recent version
 task integTest {
     if (project.bwc_tests_enabled) {
-        dependsOn = ["v${indexCompatVersions[-1]}#bwcTest"]
+        for (final def version : versionCollection.basicIntegrationTestVersions) {
+            dependsOn "v${version}#bwcTest"
+        }
     }
 }
 

qa/rolling-upgrade/build.gradle

@@ -29,7 +29,7 @@ task bwcTest {
   group = 'verification'
 }
 
-for (Version version : wireCompatVersions) {
+for (Version version : versionCollection.versionsWireCompatibleWithCurrent) {
   String baseName = "v${version}"
 
   Task oldClusterTest = tasks.create(name: "${baseName}#oldClusterTest", type: RestIntegTestTask) {
@@ -111,7 +111,9 @@ test.enabled = false // no unit tests for rolling upgrades, only the rest integr
 // basic integ tests includes testing bwc against the most recent version
 task integTest {
   if (project.bwc_tests_enabled) {
-    dependsOn = ["v${wireCompatVersions[-1]}#bwcTest"]
+    for (final def version : versionCollection.basicIntegrationTestVersions) {
+      dependsOn "v${version}#bwcTest"
+    }
   }
 }
 

qa/verify-version-constants/build.gradle

@@ -31,7 +31,7 @@ task bwcTest {
     group = 'verification'
 }
 
-for (Version version : indexCompatVersions) {
+for (Version version : versionCollection.versionsIndexCompatibleWithCurrent) {
     String baseName = "v${version}"
     Task oldClusterTest = tasks.create(name: "${baseName}#oldClusterTest", type: RestIntegTestTask) {
         mustRunAfter(precommit)
@@ -57,7 +57,9 @@ for (Version version : indexCompatVersions) {
 test.enabled = false
 
 task integTest {
-    dependsOn = ["v${indexCompatVersions[-1]}#bwcTest"]
+    for (final def version : versionCollection.basicIntegrationTestVersions) {
+        dependsOn "v${version}#bwcTest"
+    }
 }
 
 task verifyDocsLuceneVersion {

settings.gradle

@@ -16,8 +16,6 @@ List projects = [
   'client:benchmark',
   'benchmarks',
   'distribution:integ-test-zip',
-  'distribution:bwc-release-snapshot',
-  'distribution:bwc-stable-snapshot',
   'distribution:zip',
   'distribution:tar',
   'distribution:deb',
@@ -97,6 +95,12 @@ for (File example : examplePluginsDir.listFiles()) {
   examplePlugins.add(example.name)
 }
 
+/* Create projects for building BWC snapshot distributions from the heads of other branches */
+final List<String> branches = ['5.6', '6.0', '6.1', '6.x']
+for (final String branch : branches) {
+  projects.add("distribution:bwc-snapshot-${branch}".toString())
+}
+
 boolean isEclipse = System.getProperty("eclipse.launcher") != null || gradle.startParameter.taskNames.contains('eclipse') || gradle.startParameter.taskNames.contains('cleanEclipse')
 if (isEclipse) {
   // eclipse cannot handle an intermediate dependency between main and test, so we must create separate projects
@@ -113,12 +117,11 @@ for (String example : examplePlugins) {
   project(":example-plugins:${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')
+/* The BWC snapshot projects share the same build directory and build file,
+ * but apply to different backwards compatibility branches. */
+for (final String branch : branches) {
+  project(":distribution:bwc-snapshot-${branch}").projectDir = new File(rootProject.projectDir, 'distribution/bwc')
+}
 
 if (isEclipse) {
   project(":core").projectDir = new File(rootProject.projectDir, 'core/src/main')
@@ -133,18 +136,29 @@ if (isEclipse) {
   * of the dir hierarchy to have a build.gradle. Otherwise we would have to iterate
   * all files/directories in the source tree to find all projects.
   */
-void addSubProjects(String path, File dir) {
+void addSubProjects(String path, File dir, List<String> projects, List<String> branches) {
   if (dir.isDirectory() == false) return;
   if (dir.name == 'buildSrc') return;
   if (new File(dir, 'build.gradle').exists() == false) return;
 
-  String projectName = "${path}:${dir.name}"
+  final String projectName = "${path}:${dir.name}"
   include projectName
-  if (path.isEmpty()) {
-    project(projectName).projectDir = dir
-  }
-  for (File subdir : dir.listFiles()) {
-    addSubProjects(projectName, subdir)
+
+  if (dir.name == 'bwc-snapshot-dummy-projects') {
+    for (final String branch : branches) {
+      final String snapshotProjectName = "${projectName}:bwc-snapshot-${branch}"
+      projects.add(snapshotProjectName)
+      include snapshotProjectName
+      project("${snapshotProjectName}").projectDir = dir
+    }
+    // TODO do we want to assert that there's nothing else in the bwc directory?
+  } else {
+    if (path.isEmpty()) {
+      project(projectName).projectDir = dir
+    }
+    for (File subdir : dir.listFiles()) {
+      addSubProjects(projectName, subdir, projects, branches)
+    }
   }
 }
 
@@ -152,6 +166,6 @@ void addSubProjects(String path, File dir) {
 File extraProjects = new File(rootProject.projectDir.parentFile, "${dirName}-extra")
 if (extraProjects.exists()) {
   for (File extraProjectDir : extraProjects.listFiles()) {
-    addSubProjects('', extraProjectDir)
+    addSubProjects('', extraProjectDir, projects, branches)
   }
 }

test/framework/build.gradle

@@ -69,6 +69,6 @@ task namingConventionsMain(type: org.elasticsearch.gradle.precommit.NamingConven
 precommit.dependsOn namingConventionsMain
 
 test.configure {
-  systemProperty 'tests.gradle_index_compat_versions', indexCompatVersions.join(',')
-  systemProperty 'tests.gradle_wire_compat_versions', wireCompatVersions.join(',')
+  systemProperty 'tests.gradle_index_compat_versions', versionCollection.versionsIndexCompatibleWithCurrent.join(',')
+  systemProperty 'tests.gradle_wire_compat_versions', versionCollection.versionsWireCompatibleWithCurrent.join(',')
 }