Revert "No longer throw an exception if both plugin yml and groovy exist at runtime because it should be prevented in GrailsPluginGradlePlugin"

This reverts commit c37267b.

Author: jameskleeh

grails-core/src/main/groovy/org/grails/plugins/AbstractGrailsPlugin.java

@@ -123,14 +123,19 @@ public boolean isEnabled(String[] profiles) {
     }
 
     protected Resource readPluginConfiguration(Class<?> pluginClass) {
-        Resource ymlResource = getConfigurationResource(pluginClass, PLUGIN_YML_PATH);
-        Resource groovyResource = getConfigurationResource(pluginClass, PLUGIN_GROOVY_PATH);
+        Resource ymlUrlResource = getConfigurationResource(pluginClass, PLUGIN_YML_PATH);
+        Resource groovyUrlResource = getConfigurationResource(pluginClass, PLUGIN_GROOVY_PATH);
 
-        if(ymlResource != null && ymlResource.exists()) {
-            return ymlResource;
+        Boolean groovyUrlResourceExists = groovyUrlResource != null && groovyUrlResource.exists();
+
+        if(ymlUrlResource != null && ymlUrlResource.exists()) {
+            if (groovyUrlResourceExists) {
+                throw new RuntimeException("A plugin may define a plugin.yml or a plugin.groovy, but not both");
+            }
+            return ymlUrlResource;
         }
-        if(groovyResource != null && groovyResource.exists()) {
-            return groovyResource;
+        if(groovyUrlResourceExists) {
+            return groovyUrlResource;
         }
         return null;
     }

grails-core/src/test/groovy/org/codehaus/groovy/grails/plugins/BinaryPluginSpec.groovy

@@ -51,16 +51,15 @@ class BinaryPluginSpec extends Specification {
             cssResource == null
     }
 
-    //This should never occur because the GrailsPluginGradlePlugin.groovy should catch it
-    def "Test plugin with both plugin.yml and plugin.groovy, yml is used"() {
+    def "Test plugin with both plugin.yml and plugin.groovy throws exception"() {
         when:
         def descriptor = new BinaryGrailsPluginDescriptor(new ByteArrayResource(testBinary.getBytes('UTF-8')), ['org.codehaus.groovy.grails.plugins.TestBinaryResource'])
         MockConfigBinaryGrailsPlugin.YAML_EXISTS = true
         MockConfigBinaryGrailsPlugin.GROOVY_EXISTS = true
-        def binaryPlugin = new MockConfigBinaryGrailsPlugin(descriptor)
+        new MockConfigBinaryGrailsPlugin(descriptor)
 
         then:
-        binaryPlugin.propertySource.getProperty('foo') == "bar"
+        thrown(RuntimeException)
     }
 
     def "Test plugin with only plugin.yml"() {