allow extensions to mark if it supports dynamic loading or not

core/src/main/java/hudson/Extension.java

@@ -23,6 +23,7 @@
  */
 package hudson;
 
+import jenkins.YesNoMaybe;
 import net.java.sezpoz.Indexable;
 
 import java.lang.annotation.Documented;
@@ -31,6 +32,7 @@ import java.lang.annotation.Target;
 
 import static java.lang.annotation.ElementType.*;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
+import static jenkins.YesNoMaybe.MAYBE;
 
 /**
  * Marks a field, a method, or a class for automatic discovery, so that Hudson can locate
@@ -84,4 +86,20 @@ public @interface Extension {
      * @since 1.358
      */
     boolean optional() default false;
+
+    /**
+     * Marks whether this extension works with dynamic loading of a plugin.
+     *
+     * <p>
+     * "Yes" indicates an explicit sign-off from the developer indicating this component supports that.
+     * Similarly, "No" indicates that this extension is known not to support it, which forces Jenkins
+     * not to offer dynamic loading as an option.
+     *
+     * <p>
+     * The "MayBe" value indicates that there's no such explicit sign-off. So the dynamic loading may or may not
+     * work.
+     *
+     * @since 1.DynamicExtensionFinder
+     */
+    YesNoMaybe dynamicLoadable() default MAYBE;
 }

core/src/main/java/jenkins/YesNoMaybe.java

+/*
+ * The MIT License
+ *
+ * Copyright (c) 2011, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package jenkins;
+
+/**
+ * Enum that represents {@link Boolean} state (including null for the absence.)
+ *
+ * <p>
+ * This is for situations where we can't use {@link Boolean}, such as annotation elements.
+ *
+ * @author Kohsuke Kawaguchi
+ */
+public enum YesNoMaybe {
+    YES,
+    NO,
+    MAYBE;
+
+    public static Boolean toBoolean(YesNoMaybe v) {
+        if (v==null)    return null;
+        return v.toBool();
+    }
+    
+    public Boolean toBool() {
+        switch (this) {
+        case YES:
+            return true;
+        case NO:
+            return false;
+        default:
+            return null;
+        }
+    }
+}