Fix build on sles with new docker version (#36707)

The build hash for some Docker versions is
longer than 7 characters.

Closes #36414

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

@@ -293,18 +293,7 @@ class BuildPlugin implements Plugin<Project> {
                                 it.standardOutput = dockerVersionOutput
                             })
                     final String dockerVersion = dockerVersionOutput.toString().trim()
-                    final Matcher matcher = dockerVersion =~ /Docker version (\d+\.\d+)\.\d+(?:-ce)?, build [0-9a-f]{7}/
-                    assert matcher.matches() : dockerVersion
-                    final dockerMajorMinorVersion = matcher.group(1)
-                    final String[] majorMinor = dockerMajorMinorVersion.split("\\.")
-                    if (Integer.parseInt(majorMinor[0]) < 17
-                            || (Integer.parseInt(majorMinor[0]) == 17 && Integer.parseInt(majorMinor[1]) < 5)) {
-                        final String message = String.format(
-                                Locale.ROOT,
-                                "building Docker images requires Docker version 17.05+ due to use of multi-stage builds yet was [%s]",
-                                dockerVersion)
-                        throwDockerRequiredException(message)
-                    }
+                    checkDockerVersionRecent(dockerVersion)
 
                     final ByteArrayOutputStream dockerImagesErrorOutput = new ByteArrayOutputStream()
                     // the Docker binary executes, check that we can execute a privileged command
@@ -339,6 +328,21 @@ class BuildPlugin implements Plugin<Project> {
         }
     }
 
+    protected static void checkDockerVersionRecent(String dockerVersion) {
+        final Matcher matcher = dockerVersion =~ /Docker version (\d+\.\d+)\.\d+(?:-ce)?, build [0-9a-f]{7,40}/
+        assert matcher.matches(): dockerVersion
+        final dockerMajorMinorVersion = matcher.group(1)
+        final String[] majorMinor = dockerMajorMinorVersion.split("\\.")
+        if (Integer.parseInt(majorMinor[0]) < 17
+                || (Integer.parseInt(majorMinor[0]) == 17 && Integer.parseInt(majorMinor[1]) < 5)) {
+            final String message = String.format(
+                    Locale.ROOT,
+                    "building Docker images requires Docker version 17.05+ due to use of multi-stage builds yet was [%s]",
+                    dockerVersion)
+            throwDockerRequiredException(message)
+        }
+    }
+
     private static void throwDockerRequiredException(final String message) {
         throw new GradleException(
                 message + "\nyou can address this by attending to the reported issue, "

buildSrc/src/test/groovy/org/elasticsearch/gradle/BuildPluginTests.java

@@ -0,0 +1,39 @@
+/*
+ * 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.elasticsearch.gradle.test.GradleUnitTestCase;
+import org.gradle.api.GradleException;
+import org.junit.Test;
+
+
+public class BuildPluginTests extends GradleUnitTestCase {
+
+    public void testPassingDockerVersions() {
+        BuildPlugin.checkDockerVersionRecent("Docker version 18.06.1-ce, build e68fc7a215d7");
+        BuildPlugin.checkDockerVersionRecent("Docker version 17.05.0, build e68fc7a");
+        BuildPlugin.checkDockerVersionRecent("Docker version 17.05.1, build e68fc7a");
+    }
+
+    @Test(expected = GradleException.class)
+    public void testFailingDockerVersions() {
+        BuildPlugin.checkDockerVersionRecent("Docker version 17.04.0, build e68fc7a");
+    }
+
+}