Gradle 2.9 unsupported error

- Throws explanatory error for gradle version 2.9 or later
- Meant to be temporary until j2objc-contrib#568 is fixed
- Fixes j2objc-contrib#581 (Gradle 2.9 unsupported message)
- Fixes j2objc-contrib#585 (Gradle deadlock on unsupported version)

src/main/groovy/com/github/j2objccontrib/j2objcgradle/J2objcConfig.groovy

@@ -733,6 +733,20 @@ class J2objcConfig {
      */
     @VisibleForTesting
     void finalConfigure() {
+
+        // Gradle 2.9 build will fail if it calls configureNativeCompilation:
+        //     https://github.com/j2objc-contrib/j2objc-gradle/issues/568
+        // Return early without error to avoid deadlock:
+        //     https://github.com/j2objc-contrib/j2objc-gradle/issues/585
+        // Exception is thrown when TranslateTask is run. Safest approach is to disable
+        // all setup logic even though only NativeCompilation appears to cause any issue.
+        if (Utils.checkGradleVersion(false)) {
+            configureNativeCompilationForUnsupported()
+            // Avoid misleading error message that finalConfigured() wasn't in build.gradle
+            finalConfigured = true
+            return
+        }
+
         validateConfiguration()
         // Conversion of compile and testCompile dependencies occurs optionally.
         if (autoConfigureDeps) {
@@ -840,6 +854,10 @@ class J2objcConfig {
                                 project.file("${project.buildDir}/j2objcSrcGenTest"))
     }
 
+    protected void configureNativeCompilationForUnsupported() {
+        nativeCompilation.applyWhenUnsupported()
+    }
+
     protected void convertDeps() {
         new DependencyConverter(project, this).configureAll()
     }

src/main/groovy/com/github/j2objccontrib/j2objcgradle/J2objcPlugin.groovy

@@ -32,7 +32,6 @@ import org.gradle.api.Project
 import org.gradle.api.Task
 import org.gradle.api.plugins.JavaPlugin
 import org.gradle.api.logging.LogLevel
-import org.gradle.util.GradleVersion
 
 /*
  * Main plugin class for creation of extension object and all the tasks.
@@ -56,7 +55,6 @@ class J2objcPlugin implements Plugin<Project> {
 
         // This avoids a lot of "project." prefixes, such as "project.tasks.create"
         project.with {
-            Utils.checkMinGradleVersion(GradleVersion.current())
             getPluginManager().apply(JavaPlugin)
 
             extensions.create('j2objcConfig', J2objcConfig, project)

src/main/groovy/com/github/j2objccontrib/j2objcgradle/NativeCompilation.groovy

@@ -19,6 +19,7 @@ package com.github.j2objccontrib.j2objcgradle
 import com.github.j2objccontrib.j2objcgradle.tasks.Utils
 import groovy.transform.PackageScope
 import org.gradle.api.Action
+import org.gradle.api.DefaultTask
 import org.gradle.api.InvalidUserDataException
 import org.gradle.api.NamedDomainObjectContainer
 import org.gradle.api.Project
@@ -121,6 +122,18 @@ class NativeCompilation {
         })
     }
 
+    // Creates fake tasks to satisfy dependencies for J2objcPlugin.apply(...)
+    // Should only be used as an alternative to NativeComplication.apply(...) when
+    // the Gradle Version is unsupported and no J2ObjC is possible.
+    void applyWhenUnsupported() {
+        project.with {
+            tasks.create(name: 'debugTestJ2objcExecutable', type: DefaultTask)
+            tasks.create(name: 'releaseTestJ2objcExecutable', type: DefaultTask)
+            tasks.create(name: 'j2objcBuildObjcDebug', type: DefaultTask)
+            tasks.create(name: 'j2objcBuildObjcRelease', type: DefaultTask)
+        }
+    }
+
     @PackageScope
     @SuppressWarnings("grvy:org.codenarc.rule.size.NestedBlockDepthRule")
     void apply(File srcGenMainDir, File srcGenTestDir) {

src/main/groovy/com/github/j2objccontrib/j2objcgradle/tasks/TranslateTask.groovy

@@ -135,6 +135,11 @@ class TranslateTask extends DefaultTask {
 
     @TaskAction
     void translate(IncrementalTaskInputs inputs) {
+        // Exceptions must be delayed until Plugin tasks are run
+        // Doing it earlier causes Gradle deadlock:
+        // https://github.com/j2objc-contrib/j2objc-gradle/issues/585
+        Utils.checkGradleVersion(true)
+
         List<String> translateArgs = getTranslateArgs()
         // Don't evaluate this expensive property multiple times.
         FileCollection originalMainSrcFiles = getMainSrcFiles()

src/main/groovy/com/github/j2objccontrib/j2objcgradle/tasks/Utils.groovy

@@ -55,12 +55,33 @@ class Utils {
     // Prevent construction of this class, confines usage to static methods
     private Utils() { }
 
-    static void checkMinGradleVersion(GradleVersion gradleVersion) {
+    static boolean checkGradleVersion(boolean throwIfUnsupported) {
+        return checkGradleVersion(GradleVersion.current(), throwIfUnsupported)
+    }
+
+    @VisibleForTesting
+    static boolean checkGradleVersion(GradleVersion gradleVersion, boolean throwIfUnsupported) {
+        String errorMsg = ''
+
         final GradleVersion minGradleVersion = GradleVersion.version('2.4')
-        if (gradleVersion.compareTo(minGradleVersion) < 0) {
-            throw new InvalidUserDataException(
-                    "J2ObjC Gradle Plugin requires minimum Gradle version: $minGradleVersion")
+        if (gradleVersion.compareTo(GradleVersion.version('2.4')) < 0) {
+            errorMsg = "J2ObjC Gradle Plugin requires minimum Gradle version: $minGradleVersion"
+        }
+
+        final GradleVersion unsupportedGradleVersion = GradleVersion.version('2.9')
+        if (gradleVersion.compareTo(unsupportedGradleVersion) >= 0) {
+            errorMsg = "Please use Gradle 2.8 as $unsupportedGradleVersion is unsupported:\n" +
+                       "https://github.com/j2objc-contrib/j2objc-gradle/issues/568"
+        }
+
+        if (!errorMsg.isEmpty()) {
+            if (throwIfUnsupported) {
+                throw new InvalidUserDataException(errorMsg)
+            } else {
+                return true
+            }
         }
+        return false
     }
 
     static List<Integer> parseVersionComponents(String ver) {

src/test/groovy/com/github/j2objccontrib/j2objcgradle/tasks/UtilsTest.groovy

@@ -58,17 +58,35 @@ class UtilsTest {
     }
 
     @Test
-    void testCheckMinGradleVersion_valid() {
-        Utils.checkMinGradleVersion(GradleVersion.version('2.4'))
-        Utils.checkMinGradleVersion(GradleVersion.version('2.4.1'))
-        Utils.checkMinGradleVersion(GradleVersion.version('2.5'))
-        Utils.checkMinGradleVersion(GradleVersion.version('3.0'))
-        Utils.checkMinGradleVersion(GradleVersion.version('10.0'))
+    void testCheckGradleVersion_valid() {
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.4'), false)
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.4.1'), false)
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.5'), false)
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.8'), false)
+    }
+
+    @Test
+    void testCheckGradleVersion_validAndThrowIfUnsupported() {
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.4'), true)
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.4.1'), true)
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.5'), true)
+        assert !Utils.checkGradleVersion(GradleVersion.version('2.8'), true)
+    }
+
+    @Test
+    void testCheckGradleVersion_invalid() {
+        assert Utils.checkGradleVersion(GradleVersion.version('2.3'), false)
+        assert Utils.checkGradleVersion(GradleVersion.version('2.9'), false)
+    }
+
+    @Test(expected=InvalidUserDataException)
+    void testCheckGradleVersion_invalidBelowMinimum() {
+        Utils.checkGradleVersion(GradleVersion.version('2.3'), true)
     }
 
     @Test(expected=InvalidUserDataException)
-    void testCheckMinGradleVersion_invalid() {
-        Utils.checkMinGradleVersion(GradleVersion.version('2.3'))
+    void testCheckGradleVersion_invalidAboveMaximum() {
+        Utils.checkGradleVersion(GradleVersion.version('2.9'), true)
     }
 
     @Test