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+/* Processor.java -- An annotation processor.
+   Copyright (C) 2012  Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+package javax.annotation.processing;
+
+import java.util.Set;
+
+import javax.lang.model.SourceVersion;
+import javax.lang.model.element.TypeElement;
+
+/**
+ * <p>Provides the interface for an annotation processor.</p>
+ * <p>Annotation processing is divided into a series of rounds,
+ * with the input for each round being a subset of the output
+ * from the previous round.  The input for the initial round
+ * are those provided to the tool by the user, but, for the
+ * purposes of operation, can be thought of as coming from a
+ * virtual preceding round, as the behaviour is the same.
+ * Once a processor is asked to process inputs in a particular
+ * round, it is asked to do so in all subsequent rounds, even
+ * if there are no annotations left for it to process.  These
+ * inputs can include files generated by the tool's operation.</p>
+ * <p>Annotation processors are found using a tool-specific
+ * discovery method which may involve them being named directly
+ * or discovered via a service-based lookup.  The processors which
+ * are actually used are determined by which of the annotations present
+ * on the root elements are supported by the processor and whether or
+ * not it claims them.  Claimed annotation types are removed from
+ * the set of unmatched annotations and are not passed to other
+ * processors.  A round is complete once the set is empty or no
+ * more processors are available.  If there are no annotation types
+ * on the root elements (i.e. the set is empty to begin with), then
+ * only <emph>universal processors</emph> (those which accept {@code "*"})
+ * are run.</p>
+ * <h2>Implementing an Annotation Processor</h2>
+ * <p>The tool infrastructure expects the following from an annotation
+ * processor:</p>
+ * <ol>
+ * <li>It should be able to create an instance of the processor using
+ * a no-argument constructor and use this same instance for the whole run.</li>
+ * <li>Once it has created the instance, it calls {@code init} with
+ * an appropriate {@link ProcessingEnvironment}.</li>
+ * <li>The tool calls {@link #getSupportedAnnotationTypes},
+ * {@link #getSupportedOptions} and {@link #getSupportedSourceVersion} once
+ * at the start of each run.</li>
+ * <li>The tool calls {@link #process} on the processor for each round.</li>
+ * </ol>
+ * <p>Use outside the above protocol is undefined.  A processor supporting
+ * {@code "*"} and returning {@code true} from the {@code process} method
+ * will claim all annotations and prevent other processors from running.
+ * If this is not the intention, then {@code false} should be returned.</p>
+ * <p>To work well with different tool implementations, the processor
+ * should make sure the following properties hold:</p>
+ * <ol>
+ * <li><strong>Orthogonality</strong>: The result of processing an input
+ * is not dependent on the presence or not of other inputs.</li>
+ * <li><strong>Consistency</strong>: Processing the same input should
+ * always produce the same output.</li>
+ * <li><strong>Commutativity</strong>: Processing input A then input B
+ * should be the same as processing input B then input A.</li>
+ * <li><strong>Independence</strong>: The result of processing an input
+ * is not dependent on the presence of output from other processors.</li>
+ * </ol>
+ * <p>If a processor raises an error, this will be noted and the round
+ * completed.  The subsequent round can then query as to whether an
+ * error was raised using {@link RoundEnvironment#errorRaised()}.  If
+ * an uncaught exception is raised, the tool may cease the use of other
+ * annotation processors, so this should be used only in situations where
+ * the usual error recovery process is infeasible.</p>
+ * <p>The tool environment need not support annotation processors accessing
+ * environmental resources, either per round or cross-round, in a multi-threaded
+ * environment.  If a method returns {@code null} or other invalid input, or throws
+ * an exception, in response to a configuration query, the tool may treat this
+ * as an error condition.</p>
+ * <p>The {@link Filer} interface documentation provides more information on how
+ * files are handled and the restrictions in place.  Implementators may find it
+ * easier to base their implementation on the {@link AbstractProcessor} class
+ * rather than implementing this interface directly.</p>
+ *
+ * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
+ * @since 1.6
+ */
+public interface Processor
+{
+
+  /**
+   * <p>Returns the names of the annotation types supported by this
+   * processor.  These can take one of the following forms:</p>
+   * <ol>
+   * <li>A canonical fully-qualified type name.</li>
+   * <li>A partial type name with the suffix {@code .*}</li>
+   * <li>{@code .*}</li>
+   * </ol>
+   * <p>For example, {@code "gnu.classpath.annotations.ProcessMe"} matches
+   * the specific annotation class, {@code ProcessMe}.  Alternatively,
+   * {@code "gnu.classpath.annotations.*"} matches all annotations under
+   * the package {@code gnu.classpath.annotations}.  Finally, {@code .*}
+   * matches all annotations.</p>
+   * <p>Processors should avoid claiming annotations they don't support,
+   * as this may cause performance issues, and, if they also return
+   * {@code true} when asked to {@link #process()} them, then they may
+   * prevent other processors from handling those annotations.</p>
+   *
+   * @return the names of the supported annotation types.
+   * @see SupportedAnnotationTypes
+   */
+  Set<String> getSupportedAnnotationTypes();
+
+  /**
+   * Returns the options supported by this tool.  Each string
+   * returned by this method must be a period-separated sequence
+   * of identifiers, as defined by
+   * {@link SourceVersion#isIdentifier(CharSequence)}.
+   * The tool may use this list to work out which options a user
+   * provides are unsupported and print a warning.
+   *
+   * @return the names of the supported options or an empty set if none.
+   * @see SupportedOptions
+   */
+  Set<String> getSupportedOptions();
+
+  /**
+   * Returns the latest source code version supported by this processor.
+   *
+   * @return the latest version supported.
+   * @see SupportedSourceVersion
+   * @see ProcessingEnvironment#getSourceVersion
+   */
+  SourceVersion getSupportedSourceVersion();
+
+  /**
+   * Initialises the processor with the specified environment.
+   *
+   * @param env the environment for the annotation processor, which gives
+   *            it with access to facilities provided by the tool.
+   */
+  void init(ProcessingEnvironment env);
+
+  /**
+   * Processes a set of annotation types originating from the previous
+   * round (including the virtual zeroth round formed from the user's input).
+   * The processor may opt to claim these types by returning {@code true}.
+   * If it does so, the types are claimed and they are not passed to
+   * subsequent processors.  Whether a processor claims types or not may
+   * vary, dependent on its own criteria.  A processor that supports
+   * all types ({@code "*"}) is expected to gracefully handle the possibility
+   * of receiving an empty set of annotations.
+   *
+   * @param types the annotations to process.
+   * @param roundEnv information about this and the previous round.
+   * @return true if the annotations are claimed by this processor, false otherwise.
+   */
+  boolean process(Set<? extends TypeElement> types, RoundEnvironment roundEnv);
+
+}
+