Fix plugins {...} syntax by allowing reordering of plugin loading

README.md

@@ -38,9 +38,10 @@ Tracked issue: https://github.com/j2objc-contrib/j2objc-gradle/issues/130**
         xcodeProjectDir "${projectDir}/../ios"   // Xcode workspace directory
         xcodeTarget "IosApp"                     // Xcode application target name
 
-        // More: https://github.com/j2objc-contrib/j2objc-gradle/blob/master/src/main/groovy/com/github/j2objccontrib/j2objcgradle/J2objcPluginExtension.groovy#L25
+        // Help information on other settings:
+        // https://github.com/j2objc-contrib/j2objc-gradle/blob/master/src/main/groovy/com/github/j2objccontrib/j2objcgradle/J2objcPluginExtension.groovy#L25
 
-        // You must include this call (at the end of the block) even if you do not configure any other settings.
+        // You must include this call (at the end of j2objcConfig) regardless of settings
         finalConfigure()
     }
 

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

@@ -37,21 +37,16 @@ class J2objcPlugin implements Plugin<Project> {
     void apply(Project project) {
         // This avoids a lot of "project." prefixes, such as "project.tasks.create"
         project.with {
-            if (!plugins.hasPlugin('java')) {
-                def message =
-                        "j2objc plugin didn't find the 'java' plugin in the '${project.name}' project.\n"+
-                        "This is a requirement for using j2objc. Please see usage information at:\n" +
-                        "\n" +
-                        "https://github.com/j2objc-contrib/j2objc-gradle/#usage"
-                throw new InvalidUserDataException(message)
-            }
-
             extensions.create('j2objcConfig', J2objcPluginExtension, project)
+
             afterEvaluate { evaluatedProject ->
+
                 // Validate minimally required parameters.
                 // j2objcHome() will throw the appropriate exception internally.
                 assert J2objcUtils.j2objcHome(evaluatedProject)
 
+                J2objcUtils.throwIfNoJavaPlugin(evaluatedProject)
+
                 if (!evaluatedProject.j2objcConfig.isFinalConfigured()) {
                     def message = "You must call finalConfigure() in j2objcConfig, ex:\n" +
                                   "j2objcConfig {\n" +

src/main/groovy/com/github/j2objccontrib/j2objcgradle/tasks/J2objcUtils.groovy

@@ -40,8 +40,21 @@ class J2objcUtils {
         return System.getProperty('os.name').toLowerCase().contains('windows')
     }
 
+    static void throwIfNoJavaPlugin(Project proj) {
+        if (!proj.plugins.hasPlugin('java')) {
+            String message =
+                    "j2objc plugin didn't find the 'java' plugin in the '${proj.name}' project.\n" +
+                    "This is a requirement for using j2objc. Please see usage information at:\n" +
+                    "\n" +
+                    "https://github.com/j2objc-contrib/j2objc-gradle/#usage"
+            throw new InvalidUserDataException(message)
+        }
+    }
+
     // Retrieves the configured source directories from the Java plugin SourceSets.
     static SourceDirectorySet srcDirs(Project proj, String sourceSetName, String fileType) {
+        throwIfNoJavaPlugin(proj)
+
         assert fileType == 'java' || fileType == 'resources'
         assert sourceSetName == 'main' || sourceSetName == 'test'
         SourceSet sourceSet = proj.sourceSets.findByName(sourceSetName)

src/test/groovy/com/github/j2objccontrib/j2objcgradle/tasks/J2objcUtilsTest.groovy

@@ -42,6 +42,13 @@ public class J2objcUtilsTest {
         J2objcUtils.isWindows()
     }
 
+    @Test(expected = InvalidUserDataException.class)
+    public void testThrowIfNoJavaPlugin_NoJavaPlugin() {
+        J2objcUtils.throwIfNoJavaPlugin(proj)
+    }
+
+    // TODO: testThrowIfNoJavaPlugin_JavaPluginExists
+
     // TODO: testSrcDirs() - requires 'java' plugin
 
     // TODO: testSourcepathJava() - requires 'java' plugin