chore: update GRADLE_MIN_VERSION in check and test suite to 4.0

src/main/java/com/google/cloud/tools/gradle/appengine/AppEnginePlugin.java

@@ -19,6 +19,7 @@
 
 import com.google.cloud.tools.gradle.appengine.appyaml.AppEngineAppYamlPlugin;
 import com.google.cloud.tools.gradle.appengine.standard.AppEngineStandardPlugin;
+import com.google.cloud.tools.gradle.appengine.util.GradleCompatibility;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import org.gradle.api.GradleException;
@@ -34,8 +35,6 @@
  */
 public class AppEnginePlugin implements Plugin<Project> {
 
-  private static final GradleVersion GRADLE_MIN_VERSION = GradleVersion.version("3.4.1");
-
   @Override
   public void apply(Project project) {
     checkGradleVersion();
@@ -63,12 +62,12 @@ private boolean isAppEngineWebXmlBased(Project project) {
   }
 
   private void checkGradleVersion() {
-    if (GRADLE_MIN_VERSION.compareTo(GradleVersion.current()) > 0) {
+    if (GradleCompatibility.getMinimumGradleVersion().compareTo(GradleVersion.current()) > 0) {
       throw new GradleException(
           "Detected "
               + GradleVersion.current()
               + ", but the appengine-gradle-plugin requires "
-              + GRADLE_MIN_VERSION
+              + GradleCompatibility.getMinimumGradleVersion()
               + " or higher.");
     }
   }

src/main/java/com/google/cloud/tools/gradle/appengine/core/AppEngineCorePluginConfiguration.java

@@ -18,6 +18,7 @@
 package com.google.cloud.tools.gradle.appengine.core;
 
 import com.google.cloud.tools.appengine.operations.cloudsdk.CloudSdkNotFoundException;
+import com.google.cloud.tools.gradle.appengine.util.GradleCompatibility;
 import com.google.cloud.tools.managedcloudsdk.BadCloudSdkVersionException;
 import com.google.cloud.tools.managedcloudsdk.ManagedCloudSdk;
 import com.google.cloud.tools.managedcloudsdk.UnsupportedOsException;
@@ -32,8 +33,6 @@
  */
 public class AppEngineCorePluginConfiguration {
 
-  public static final GradleVersion GRADLE_MIN_VERSION = GradleVersion.version("3.4.1");
-
   public static final String LOGIN_TASK_NAME = "appengineCloudSdkLogin";
   public static final String DEPLOY_TASK_NAME = "appengineDeploy";
   public static final String DEPLOY_CRON_TASK_NAME = "appengineDeployCron";
@@ -336,12 +335,12 @@ private void createShowConfigurationTask() {
   }
 
   private void checkGradleVersion() {
-    if (GRADLE_MIN_VERSION.compareTo(GradleVersion.current()) > 0) {
+    if (GradleCompatibility.getMinimumGradleVersion().compareTo(GradleVersion.current()) > 0) {
       throw new GradleException(
           "Detected "
               + GradleVersion.current()
               + ", but the appengine-gradle-plugin requires "
-              + GRADLE_MIN_VERSION
+              + GradleCompatibility.getMinimumGradleVersion()
               + " or higher.");
     }
   }

src/main/java/com/google/cloud/tools/gradle/appengine/util/GradleCompatibility.java

@@ -11,6 +11,16 @@ private GradleCompatibility() {
     // Prevent instantiation and extension.
   }
 
+  /**
+   * Method for getting the minimum version of Gradle supported by the plugin, for use in
+   * enforcement checks and test suite.
+   *
+   * @return the minimum compatible {@link GradleVersion}.
+   */
+  public static GradleVersion getMinimumGradleVersion() {
+    return GradleVersion.version("4.0");
+  }
+
   /**
    * Compatibility method for getting the archive location.
    *

src/test/java/com/google/cloud/tools/gradle/appengine/AppEnginePluginTest.java

@@ -25,8 +25,8 @@
 import static org.junit.Assume.assumeTrue;
 
 import com.google.cloud.tools.gradle.appengine.appyaml.AppEngineAppYamlPlugin;
-import com.google.cloud.tools.gradle.appengine.core.AppEngineCorePluginConfiguration;
 import com.google.cloud.tools.gradle.appengine.standard.AppEngineStandardPlugin;
+import com.google.cloud.tools.gradle.appengine.util.GradleCompatibility;
 import java.io.IOException;
 import org.gradle.api.Project;
 import org.gradle.testkit.runner.BuildResult;
@@ -49,7 +49,7 @@ public void testCheckGradleVersion_pass() {
     assumeTrue(isJava8Runtime());
     new TestProject(testProjectRoot.getRoot())
         .applyGradleRunnerWithGradleVersion(
-            AppEngineCorePluginConfiguration.GRADLE_MIN_VERSION.getVersion());
+            GradleCompatibility.getMinimumGradleVersion().getVersion());
     // pass
   }
 
@@ -65,7 +65,7 @@ public void testCheckGradleVersion_fail() throws IOException {
           ex.getMessage(),
           containsString(
               "Detected Gradle 2.8, but the appengine-gradle-plugin requires "
-                  + AppEngineCorePluginConfiguration.GRADLE_MIN_VERSION
+                  + GradleCompatibility.getMinimumGradleVersion()
                   + " or higher."));
     }
   }

src/test/java/com/google/cloud/tools/gradle/appengine/appyaml/AppEngineAppYamlPluginTest.java

@@ -26,8 +26,8 @@
 
 import com.google.cloud.tools.gradle.appengine.BuildResultFilter;
 import com.google.cloud.tools.gradle.appengine.TestProject;
-import com.google.cloud.tools.gradle.appengine.core.AppEngineCorePluginConfiguration;
 import com.google.cloud.tools.gradle.appengine.core.DeployExtension;
+import com.google.cloud.tools.gradle.appengine.util.GradleCompatibility;
 import com.google.common.collect.ImmutableList;
 import java.io.File;
 import java.io.IOException;
@@ -65,7 +65,7 @@ public void testCheckGradleVersion_pass() throws IOException {
     assumeTrue(isJava8Runtime());
     createTestProject()
         .applyGradleRunnerWithGradleVersion(
-            AppEngineCorePluginConfiguration.GRADLE_MIN_VERSION.getVersion());
+            GradleCompatibility.getMinimumGradleVersion().getVersion());
     // pass
   }
 
@@ -79,7 +79,7 @@ public void testCheckGradleVersion_fail() throws IOException {
           ex.getMessage(),
           containsString(
               "Detected Gradle 2.8, but the appengine-gradle-plugin requires "
-                  + AppEngineCorePluginConfiguration.GRADLE_MIN_VERSION
+                  + GradleCompatibility.getMinimumGradleVersion()
                   + " or higher."));
     }
   }

src/test/java/com/google/cloud/tools/gradle/appengine/standard/AppEngineStandardPluginTest.java

@@ -25,8 +25,8 @@
 
 import com.google.cloud.tools.gradle.appengine.BuildResultFilter;
 import com.google.cloud.tools.gradle.appengine.TestProject;
-import com.google.cloud.tools.gradle.appengine.core.AppEngineCorePluginConfiguration;
 import com.google.cloud.tools.gradle.appengine.core.DeployExtension;
+import com.google.cloud.tools.gradle.appengine.util.GradleCompatibility;
 import com.google.common.collect.ImmutableList;
 import java.io.File;
 import java.io.IOException;
@@ -69,7 +69,7 @@ public void testCheckGradleVersion_pass() throws IOException {
     assumeTrue(isJava8Runtime());
     createTestProject()
         .applyGradleRunnerWithGradleVersion(
-            AppEngineCorePluginConfiguration.GRADLE_MIN_VERSION.getVersion());
+            GradleCompatibility.getMinimumGradleVersion().getVersion());
     // pass
   }
 
@@ -83,7 +83,7 @@ public void testCheckGradleVersion_fail() throws IOException {
           ex.getMessage(),
           containsString(
               "Detected Gradle 2.8, but the appengine-gradle-plugin requires "
-                  + AppEngineCorePluginConfiguration.GRADLE_MIN_VERSION
+                  + GradleCompatibility.getMinimumGradleVersion()
                   + " or higher."));
     }
   }