Determine the minimum gradle version based on the wrapper

build.gradle

@@ -16,21 +16,17 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-
 import com.github.jengelman.gradle.plugins.shadow.ShadowPlugin
-import org.apache.tools.ant.taskdefs.condition.Os
-import org.apache.tools.ant.filters.ReplaceTokens
 import org.elasticsearch.gradle.BuildPlugin
 import org.elasticsearch.gradle.LoggedExec
 import org.elasticsearch.gradle.Version
 import org.elasticsearch.gradle.VersionCollection
 import org.elasticsearch.gradle.VersionProperties
 import org.gradle.plugins.ide.eclipse.model.SourceFolder
-
-import org.gradle.api.tasks.wrapper.Wrapper
-import org.gradle.api.tasks.wrapper.Wrapper.DistributionType
 import org.gradle.util.GradleVersion
 import org.gradle.util.DistributionLocator
+import org.apache.tools.ant.taskdefs.condition.Os
+import org.apache.tools.ant.filters.ReplaceTokens
 
 import java.nio.file.Files
 import java.nio.file.Path
@@ -537,7 +533,7 @@ task run(type: Run) {
 }
 
 wrapper {
-    distributionType = DistributionType.ALL
+    distributionType = 'ALL'
     doLast {
         final DistributionLocator locator = new DistributionLocator()
         final GradleVersion version = GradleVersion.version(wrapper.gradleVersion)
@@ -546,6 +542,10 @@ wrapper {
         final String sha256Sum = new String(sha256Uri.toURL().bytes)
         wrapper.getPropertiesFile() << "distributionSha256Sum=${sha256Sum}\n"
         println "Added checksum to wrapper properties"
+        // Update build-tools to reflect the Gradle upgrade
+        // TODO: we can remove this once we have tests to make sure older versions work.
+        project(':build-tools').file('src/main/resources/minimumGradleVersion').text = gradleVersion
+        println "Updated minimum Gradle Version"
     }
 }
 

buildSrc/build.gradle

@@ -25,8 +25,9 @@ plugins {
 
 group = 'org.elasticsearch.gradle'
 
-if (GradleVersion.current() < GradleVersion.version('4.9')) {
-  throw new GradleException('Gradle 4.9+ is required to build elasticsearch')
+String minimumGradleVersion = file('src/main/resources/minimumGradleVersion').text.trim()
+if (GradleVersion.current() < GradleVersion.version(minimumGradleVersion)) {
+    throw new GradleException("Gradle ${minimumGradleVersion}+ is required to build elasticsearch")
 }
 
 if (JavaVersion.current() < JavaVersion.VERSION_1_8) {

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

@@ -20,6 +20,7 @@ package org.elasticsearch.gradle
 
 import com.carrotsearch.gradle.junit4.RandomizedTestingTask
 import com.github.jengelman.gradle.plugins.shadow.ShadowPlugin
+import org.apache.commons.io.IOUtils
 import org.apache.tools.ant.taskdefs.condition.Os
 import org.eclipse.jgit.lib.Constants
 import org.eclipse.jgit.lib.RepositoryBuilder
@@ -53,6 +54,7 @@ import org.gradle.internal.jvm.Jvm
 import org.gradle.process.ExecResult
 import org.gradle.util.GradleVersion
 
+import java.nio.charset.StandardCharsets
 import java.time.ZoneOffset
 import java.time.ZonedDateTime
 /**
@@ -67,8 +69,13 @@ class BuildPlugin implements Plugin<Project> {
                 + 'elasticearch.standalone-rest-test, and elasticsearch.build '
                 + 'are mutually exclusive')
         }
-        if (GradleVersion.current() < GradleVersion.version('4.9')) {
-            throw new GradleException('Gradle 4.9+ is required to use elasticsearch.build plugin')
+        final String minimumGradleVersion
+        InputStream is = getClass().getResourceAsStream("/minimumGradleVersion")
+        try { minimumGradleVersion = IOUtils.toString(is, StandardCharsets.UTF_8.toString()) } finally { is.close() }
+        if (GradleVersion.current() < GradleVersion.version(minimumGradleVersion.trim())) {
+            throw new GradleException(
+                    "Gradle ${minimumGradleVersion}+ is required to use elasticsearch.build plugin"
+            )
         }
         project.pluginManager.apply('java')
         project.pluginManager.apply('carrotsearch.randomized-testing')
@@ -150,14 +157,6 @@ class BuildPlugin implements Plugin<Project> {
             }
             println "  Random Testing Seed   : ${project.testSeed}"
 
-            // enforce Gradle version
-            final GradleVersion currentGradleVersion = GradleVersion.current();
-
-            final GradleVersion minGradle = GradleVersion.version('4.3')
-            if (currentGradleVersion < minGradle) {
-                throw new GradleException("${minGradle} or above is required to build Elasticsearch")
-            }
-
             // enforce Java version
             if (compilerJavaVersionEnum < minimumCompilerVersion) {
                 final String message =

buildSrc/src/main/resources/minimumGradleVersion

@@ -0,0 +1 @@
+4.9