Fix FwC test task registration (#133937)

With this change it takes into account that not all versions have
previous minor unreleased version (because we are on the oldest active
development branch), or that current version has minor == 0 (e.g. 9.0)
so previous minor have to be calculated differently.

* Add FwC branch configuration and update periodic trigger logic

Ensuring that only relevant branches are considered.

* Correct FWC periodic pipeline variables

Utilize Buildkite matrix syntax and escape env in command.

.buildkite/pipelines/periodic-fwc.template.yml

@@ -1,6 +1,6 @@
 steps:
-  - label: $FWC_VERSION / fwc
-    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
+  - label: "{{matrix.FWC_VERSION}}" / fwc
+    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
     timeout_in_minutes: 300
     agents:
       provider: gcp
@@ -11,4 +11,4 @@ steps:
       setup:
         FWC_VERSION: $FWC_LIST
     env:
-      FWC_VERSION: $FWC_VERSION
+      FWC_VERSION: "{{matrix.FWC_VERSION}}"

.buildkite/pipelines/periodic-fwc.yml

@@ -1,7 +1,7 @@
 # This file is auto-generated. See .buildkite/pipelines/periodic-fwc.template.yml
 steps:
-  - label: $FWC_VERSION / fwc
-    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
+  - label: "{{matrix.FWC_VERSION}}" / fwc
+    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
     timeout_in_minutes: 300
     agents:
       provider: gcp
@@ -12,4 +12,4 @@ steps:
       setup:
         FWC_VERSION: []
     env:
-      FWC_VERSION: $FWC_VERSION
+      FWC_VERSION: "{{matrix.FWC_VERSION}}"

.buildkite/scripts/fwc-branches.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+# Configure FwC test branches
+# We do not want 7.x branch and only to run for branches that:
+# - have released at least one minor version (not main)
+# - have previous minor unreleased (not the oldest development branch)
+FWC_BRANCHES=()
+for branch in "${BRANCHES[@]}"; do
+  if [[ ! "$branch" =~ ^7\..* ]]; then
+    FWC_BRANCHES+=("$branch")
+  fi
+done
+# Remove first and last element
+FWC_BRANCHES=("${FWC_BRANCHES[@]:1:${#FWC_BRANCHES[@]}-2}")
+
+shouldRunFwcFor() {
+  local branch=$1
+  for fwc_branch in "${FWC_BRANCHES[@]}"; do
+    if [[ "$fwc_branch" == "$branch" ]]; then
+      return 0
+    fi
+  done
+  return 1
+}

.buildkite/scripts/periodic.trigger.sh

@@ -5,6 +5,7 @@ set -euo pipefail
 echo "steps:"
 
 source .buildkite/scripts/branches.sh
+source .buildkite/scripts/fwc-branches.sh
 
 IS_FIRST=true
 SKIP_DELAY="${SKIP_DELAY:-false}"
@@ -46,8 +47,7 @@ EOF
       branch: "$BRANCH"
       commit: "$LAST_GOOD_COMMIT"
 EOF
-# Include forward compatibility tests only for the bugfix branch
-if [[ "${BRANCH}" == "${BRANCHES[2]}" ]]; then
+if shouldRunFwcFor "$BRANCH"; then
   cat <<EOF
   - trigger: elasticsearch-periodic-fwc
     label: Trigger periodic-fwc pipeline for $BRANCH

build-tools-internal/src/main/groovy/elasticsearch.fwc-test.gradle

@@ -7,19 +7,23 @@
  * License v3.0 only", or the "Server Side Public License, v 1".
  */
 
-import org.elasticsearch.gradle.VersionProperties
+import org.elasticsearch.gradle.Version
 import org.elasticsearch.gradle.testclusters.StandaloneRestIntegTestTask
 
-def fwcVersions = buildParams.bwcVersions.released.findAll { it.major == VersionProperties.elasticsearchVersion.major &&  it.minor == VersionProperties.elasticsearchVersion.minor }
-def previousMinorSnapshot = buildParams.bwcVersions.unreleased.find { it.major == VersionProperties.elasticsearchVersion.major && it.minor == VersionProperties.elasticsearchVersion.minor - 1 }
-
-fwcVersions.each { fwcVersion ->
-  tasks.register("v${fwcVersion}#fwcTest", StandaloneRestIntegTestTask) {
-    usesBwcDistribution(previousMinorSnapshot)
-    usesBwcDistribution(fwcVersion)
-    systemProperty("tests.old_cluster_version", previousMinorSnapshot)
-    systemProperty("tests.new_cluster_version", fwcVersion)
-    nonInputProperties.systemProperty 'tests.fwc', 'true'
+Version elasticsearchVersion = Version.fromString(versions.get("elasticsearch"))
+def fwcVersions = buildParams.bwcVersions.released.findAll { it.major == elasticsearchVersion.major &&  it.minor == elasticsearchVersion.minor }
+def targetMajor = elasticsearchVersion.minor > 0 ? elasticsearchVersion.major : elasticsearchVersion.major - 1
+def targetMinor = elasticsearchVersion.minor > 0 ? elasticsearchVersion.minor - 1 : buildParams.bwcVersions.unreleased.findAll { it.major == targetMajor }*.minor.max()
+def previousMinorSnapshot = buildParams.bwcVersions.unreleased.find { it.major == targetMajor && it.minor == targetMinor }
+if (previousMinorSnapshot != null) {
+  fwcVersions.each { fwcVersion ->
+    tasks.register("v${fwcVersion}#fwcTest", StandaloneRestIntegTestTask) {
+      usesBwcDistribution(previousMinorSnapshot)
+      usesBwcDistribution(fwcVersion)
+      systemProperty("tests.old_cluster_version", previousMinorSnapshot)
+      systemProperty("tests.new_cluster_version", fwcVersion)
+      nonInputProperties.systemProperty 'tests.fwc', 'true'
+    }
   }
 }