Only validate upper bound of current branch on release branches (elastic#135391)

When transport version changes are backported they may carry along
multiple upper bounds files that have been updated. Yet in release
branches the only upper bound file that matter is that of the current
branch. This commit adjusts validation on release branches to only check
the current upper bound file.

Author: rjernst

build-tools-internal/src/integTest/groovy/org/elasticsearch/gradle/internal/transport/TransportVersionValidationFuncTest.groovy

@@ -294,4 +294,21 @@ class TransportVersionValidationFuncTest extends AbstractTransportVersionFuncTes
         then:
         result.task(":myserver:validateTransportVersionResources").outcome == TaskOutcome.SUCCESS
     }
+
+    def "only current upper bound validated on release branch"() {
+        given:
+        file("myserver/build.gradle") << """
+            tasks.named('validateTransportVersionResources') {
+                currentUpperBoundName = '9.0'
+            }
+        """
+        referableAndReferencedTransportVersion("some_tv", "8124000,8012004")
+        transportVersionUpperBound("9.1", "some_tv", "8012004")
+
+        when:
+        def result = gradleRunner("validateTransportVersionResources").build()
+
+        then:
+        result.task(":myserver:validateTransportVersionResources").outcome == TaskOutcome.SUCCESS
+    }
 }

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/ValidateTransportVersionResourcesTask.java

@@ -83,6 +83,7 @@ public void validateTransportVersions() throws IOException {
         Map<String, TransportVersionDefinition> allDefinitions = collectAllDefinitions(referableDefinitions, unreferableDefinitions);
         Map<Integer, List<IdAndDefinition>> idsByBase = collectIdsByBase(allDefinitions.values());
         Map<String, TransportVersionUpperBound> upperBounds = resources.getUpperBounds();
+        TransportVersionUpperBound currentUpperBound = upperBounds.get(getCurrentUpperBoundName().get());
         boolean onReleaseBranch = checkIfDefinitelyOnReleaseBranch(upperBounds);
 
         for (var definition : referableDefinitions.values()) {
@@ -94,14 +95,21 @@ public void validateTransportVersions() throws IOException {
         }
 
         for (var entry : idsByBase.entrySet()) {
-            validateBase(entry.getKey(), entry.getValue());
+            int baseId = entry.getKey();
+            // on main we validate all bases, but on release branches we only validate up to the current upper bound
+            if (onReleaseBranch == false || baseId <= currentUpperBound.definitionId().base()) {
+                validateBase(baseId, entry.getValue());
+            }
         }
 
-        for (var upperBound : upperBounds.values()) {
-            validateUpperBound(upperBound, allDefinitions, idsByBase);
-        }
+        if (onReleaseBranch) {
+            // on release branches we only check the current upper bound, others may be inaccurate
+            validateUpperBound(currentUpperBound, allDefinitions, idsByBase);
+        } else {
+            for (var upperBound : upperBounds.values()) {
+                validateUpperBound(upperBound, allDefinitions, idsByBase);
+            }
 
-        if (onReleaseBranch == false) {
             validatePrimaryIds(resources, upperBounds, allDefinitions);
         }
     }