Add clone of IgnoreEmptyDirectories annotation to allow compiling forbiddenapis task with it

build.xml

@@ -414,7 +414,7 @@
     <ivy:cachefileset setid="fileset.bundle" conf="bundle" log="${ivy.logging}"/>
     <mkdir dir="dist"/>
     <jarjar destfile="${jar-file}">
-      <zipfileset dir="build/main"/>
+      <zipfileset dir="build/main" excludes="org/gradle/**"/>
       <restrict>
         <name name="**/*.class" handledirsep="true"/>
         <not>

src/main/java/de/thetaphi/forbiddenapis/gradle/CheckForbiddenApis.java

@@ -40,11 +40,14 @@
 import org.gradle.api.file.FileTreeElement;
 import org.gradle.api.specs.Spec;
 import org.gradle.api.tasks.CompileClasspath;
+import org.gradle.api.tasks.IgnoreEmptyDirectories;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.InputFiles;
 import org.gradle.api.tasks.Internal;
 import org.gradle.api.tasks.Optional;
 import org.gradle.api.tasks.ParallelizableTask;
+import org.gradle.api.tasks.PathSensitive;
+import org.gradle.api.tasks.PathSensitivity;
 import org.gradle.api.tasks.SkipWhenEmpty;
 import org.gradle.api.tasks.TaskAction;
 import org.gradle.api.tasks.VerificationTask;
@@ -465,6 +468,8 @@ public CheckForbiddenApis include(@SuppressWarnings("rawtypes") Closure arg0) {
   /** Returns the classes to check. */
   @InputFiles
   @SkipWhenEmpty
+  @IgnoreEmptyDirectories
+  @PathSensitive(PathSensitivity.RELATIVE)
   public FileTree getClassFiles() {
     return getClassesDirs().getAsFileTree().matching(getPatternSet());
   }

src/main/java/org/gradle/api/tasks/IgnoreEmptyDirectories.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.gradle.api.tasks;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import de.thetaphi.forbiddenapis.gradle.CheckForbiddenApis;
+
+/**
+ * Attached to an input property to specify that directories should be ignored
+ * when snapshotting inputs. Files within directories and subdirectories will be
+ * snapshot, but the directories themselves will be ignored. Empty directories,
+ * and directories that contain only empty directories will have no effect on the
+ * resulting snapshot.
+ * <p>Copy of Gradle 6.8 annotation to allow compilation of {@link CheckForbiddenApis}.
+ * It is excluded from the JAR file (runtime annotations are still optional at runtime).
+ */
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.METHOD, ElementType.FIELD})
+public @interface IgnoreEmptyDirectories {
+}