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package javax.annotation.processing;
import java.util.Set;
import javax.lang.model.util.Elements;
import javax.lang.model.AnnotatedConstruct;
import javax.lang.model.element.*;
import javax.lang.model.SourceVersion;
/**
* The interface for an annotation processor.
*
* <p>Annotation processing happens in a sequence of {@linkplain
* javax.annotation.processing.RoundEnvironment rounds}. On each
* round, a processor may be asked to {@linkplain #process process} a
* subset of the annotations found on the source and class files
* produced by a prior round. The inputs to the first round of
* processing are the initial inputs to a run of the tool; these
* initial inputs can be regarded as the output of a virtual zeroth
* round of processing. If a processor was asked to process on a
* given round, it will be asked to process on subsequent rounds,
* including the last round, even if there are no annotations for it
* to process. The tool infrastructure may also ask a processor to
* process files generated implicitly by the tool's operation.
*
* <p> Each implementation of a {@code Processor} must provide a
* public no-argument constructor to be used by tools to instantiate
* the processor. The tool infrastructure will interact with classes
* implementing this interface as follows:
*
* <ol>
*
* <li>If an existing {@code Processor} object is not being used, to
* create an instance of a processor the tool calls the no-arg
* constructor of the processor class.
*
* <li>Next, the tool calls the {@link #init init} method with
* an appropriate {@code ProcessingEnvironment}.
*
* <li>Afterwards, the tool calls {@link #getSupportedAnnotationTypes
* getSupportedAnnotationTypes}, {@link #getSupportedOptions
* getSupportedOptions}, and {@link #getSupportedSourceVersion
* getSupportedSourceVersion}. These methods are only called once per
* run, not on each round.
*
* <li>As appropriate, the tool calls the {@link #process process}
* method on the {@code Processor} object; a new {@code Processor}
* object is <em>not</em> created for each round.
*
* </ol>
*
* If a processor object is created and used without the above
* protocol being followed, then the processor's behavior is not
* defined by this interface specification.
*
* <p> The tool uses a <i>discovery process</i> to find annotation
* processors and decide whether or not they should be run. By
* configuring the tool, the set of potential processors can be
* controlled. For example, for a {@link javax.tools.JavaCompiler
* JavaCompiler} the list of candidate processors to run can be
* {@linkplain javax.tools.JavaCompiler.CompilationTask#setProcessors
* set directly} or controlled by a {@linkplain
* javax.tools.StandardLocation#ANNOTATION_PROCESSOR_PATH search path}
* used for a {@linkplain java.util.ServiceLoader service-style}
* lookup. Other tool implementations may have different
* configuration mechanisms, such as command line options; for
* details, refer to the particular tool's documentation. Which
* processors the tool asks to {@linkplain #process run} is a function
* of the types of the annotations <em>{@linkplain AnnotatedConstruct present}</em>
* on the {@linkplain
* RoundEnvironment#getRootElements root elements}, what {@linkplain
* #getSupportedAnnotationTypes annotation types a processor
* supports}, and whether or not a processor {@linkplain #process
* claims the annotation types it processes}. A processor will be asked to
* process a subset of the annotation types it supports, possibly an
* empty set.
*
* For a given round, the tool computes the set of annotation types
* that are present on the elements enclosed within the root elements.
* If there is at least one annotation type present, then as
* processors claim annotation types, they are removed from the set of
* unmatched annotation types. When the set is empty or no more
* processors are available, the round has run to completion. If
* there are no annotation types present, annotation processing still
* occurs but only <i>universal processors</i> which support
* processing all annotation types, {@code "*"}, can claim the (empty)
* set of annotation types.
*
* <p>An annotation type is considered present if there is at least
* one annotation of that type present on an element enclosed within
* the root elements of a round. For this purpose, a type parameter is
* considered to be enclosed by its {@linkplain
* TypeParameterElement#getGenericElement generic
* element}. Annotations on {@linkplain
* java.lang.annotation.ElementType#TYPE_USE type uses}, as opposed to
* annotations on elements, are ignored when computing whether or not
* an annotation type is present.
*
* <p>An annotation is present if it meets the definition of being
* present given in {@link AnnotatedConstruct}. In brief, an
* annotation is considered present for the purposes of discovery if
* it is directly present or present via inheritance. An annotation is
* <em>not</em> considered present by virtue of being wrapped by a
* container annotation. Operationally, this is equivalent to an
* annotation being present on an element if and only if it would be
* included in the results of {@link
* Elements#getAllAnnotationMirrors(Element)} called on that element. Since
* annotations inside container annotations are not considered
* present, to properly process {@linkplain
* java.lang.annotation.Repeatable repeatable annotation types},
* processors are advised to include both the repeatable annotation
* type and its containing annotation type in the set of {@linkplain
* #getSupportedAnnotationTypes() supported annotation types} of a
* processor.
*
* <p>Note that if a processor supports {@code "*"} and returns {@code
* true}, all annotations are claimed. Therefore, a universal
* processor being used to, for example, implement additional validity
* checks should return {@code false} so as to not prevent other such
* checkers from being able to run.
*
* <p>If a processor throws an uncaught exception, the tool may cease
* other active annotation processors. If a processor raises an
* error, the current round will run to completion and the subsequent
* round will indicate an {@linkplain RoundEnvironment#errorRaised
* error was raised}. Since annotation processors are run in a
* cooperative environment, a processor should throw an uncaught
* exception only in situations where no error recovery or reporting
* is feasible.
*
* <p>The tool environment is not required to support annotation
* processors that access environmental resources, either {@linkplain
* RoundEnvironment per round} or {@linkplain ProcessingEnvironment
* cross-round}, in a multi-threaded fashion.
*
* <p>If the methods that return configuration information about the
* annotation processor return {@code null}, return other invalid
* input, or throw an exception, the tool infrastructure must treat
* this as an error condition.
*
* <p>To be robust when running in different tool implementations, an
* annotation processor should have the following properties:
*
* <ol>
*
* <li>The result of processing a given input is not a function of the presence or absence
* of other inputs (orthogonality).
*
* <li>Processing the same input produces the same output (consistency).
*
* <li>Processing input <i>A</i> followed by processing input <i>B</i>
* is equivalent to processing <i>B</i> then <i>A</i>
* (commutativity)
*
* <li>Processing an input does not rely on the presence of the output
* of other annotation processors (independence)
*
* </ol>
*
* <p>The {@link Filer} interface discusses restrictions on how
* processors can operate on files.
*
* <p>Note that implementors of this interface may find it convenient
* to extend {@link AbstractProcessor} rather than implementing this
* interface directly.
*
* @author Joseph D. Darcy
* @author Scott Seligman
* @author Peter von der Ahé
* @since 1.6
*/
public interface Processor {
/**
* Returns the options recognized by this processor. An
* implementation of the processing tool must provide a way to
* pass processor-specific options distinctly from options passed
* to the tool itself, see {@link ProcessingEnvironment#getOptions
* getOptions}.
*
* <p>Each string returned in the set must be a period separated
* sequence of {@linkplain
* javax.lang.model.SourceVersion#isIdentifier identifiers}:
*
* <blockquote>
* <dl>
* <dt><i>SupportedOptionString:</i>
* <dd><i>Identifiers</i>
*
* <dt><i>Identifiers:</i>
* <dd> <i>Identifier</i>
* <dd> <i>Identifier</i> {@code .} <i>Identifiers</i>
*
* <dt><i>Identifier:</i>
* <dd>Syntactic identifier, including keywords and literals
* </dl>
* </blockquote>
*
* <p> A tool might use this information to determine if any
* options provided by a user are unrecognized by any processor,
* in which case it may wish to report a warning.
*
* @return the options recognized by this processor or an
* empty collection if none
* @see javax.annotation.processing.SupportedOptions
*/
Set<String> getSupportedOptions();
/**
* Returns the names of the annotation types supported by this
* processor. An element of the result may be the canonical
* (fully qualified) name of a supported annotation type.
* Alternately it may be of the form "<tt><i>name</i>.*</tt>"
* representing the set of all annotation types with canonical
* names beginning with "<tt><i>name.</i></tt>". Finally, {@code
* "*"} by itself represents the set of all annotation types,
* including the empty set. Note that a processor should not
* claim {@code "*"} unless it is actually processing all files;
* claiming unnecessary annotations may cause a performance
* slowdown in some environments.
*
* <p>Each string returned in the set must be accepted by the
* following grammar:
*
* <blockquote>
* <dl>
* <dt><i>SupportedAnnotationTypeString:</i>
* <dd><i>TypeName</i> <i>DotStar</i><sub><i>opt</i></sub>
* <dd><tt>*</tt>
*
* <dt><i>DotStar:</i>
* <dd><tt>.</tt> <tt>*</tt>
* </dl>
* </blockquote>
*
* where <i>TypeName</i> is as defined in
* <cite>The Java™ Language Specification</cite>.
*
* @return the names of the annotation types supported by this processor
* @see javax.annotation.processing.SupportedAnnotationTypes
* @jls 3.8 Identifiers
* @jls 6.5.5 Meaning of Type Names
*/
Set<String> getSupportedAnnotationTypes();
/**
* Returns the latest source version supported by this annotation
* processor.
*
* @return the latest source version supported by this annotation
* processor.
* @see javax.annotation.processing.SupportedSourceVersion
* @see ProcessingEnvironment#getSourceVersion
*/
SourceVersion getSupportedSourceVersion();
/**
* Initializes the processor with the processing environment.
*
* @param processingEnv environment for facilities the tool framework
* provides to the processor
*/
void init(ProcessingEnvironment processingEnv);
/**
* Processes a set of annotation types on type elements
* originating from the prior round and returns whether or not
* these annotation types are claimed by this processor. If {@code
* true} is returned, the annotation types are claimed and subsequent
* processors will not be asked to process them; if {@code false}
* is returned, the annotation types are unclaimed and subsequent
* processors may be asked to process them. A processor may
* always return the same boolean value or may vary the result
* based on chosen criteria.
*
* <p>The input set will be empty if the processor supports {@code
* "*"} and the root elements have no annotations. A {@code
* Processor} must gracefully handle an empty set of annotations.
*
* @param annotations the annotation types requested to be processed
* @param roundEnv environment for information about the current and prior round
* @return whether or not the set of annotation types are claimed by this processor
*/
boolean process(Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv);
/**
* Returns to the tool infrastructure an iterable of suggested
* completions to an annotation. Since completions are being asked
* for, the information provided about the annotation may be
* incomplete, as if for a source code fragment. A processor may
* return an empty iterable. Annotation processors should focus
* their efforts on providing completions for annotation members
* with additional validity constraints known to the processor, for
* example an {@code int} member whose value should lie between 1
* and 10 or a string member that should be recognized by a known
* grammar, such as a regular expression or a URL.
*
* <p>Since incomplete programs are being modeled, some of the
* parameters may only have partial information or may be {@code
* null}. At least one of {@code element} and {@code userText}
* must be non-{@code null}. If {@code element} is non-{@code
* null}, {@code annotation} and {@code member} may be {@code
* null}. Processors may not throw a {@code NullPointerException}
* if some parameters are {@code null}; if a processor has no
* completions to offer based on the provided information, an
* empty iterable can be returned. The processor may also return
* a single completion with an empty value string and a message
* describing why there are no completions.
*
* <p>Completions are informative and may reflect additional
* validity checks performed by annotation processors. For
* example, consider the simple annotation:
*
* <blockquote>
* <pre>
* @MersennePrime {
* int value();
* }
* </pre>
* </blockquote>
*
* (A Mersenne prime is prime number of the form
* 2<sup><i>n</i></sup> - 1.) Given an {@code AnnotationMirror}
* for this annotation type, a list of all such primes in the
* {@code int} range could be returned without examining any other
* arguments to {@code getCompletions}:
*
* <blockquote>
* <pre>
* import static javax.annotation.processing.Completions.*;
* ...
* return Arrays.asList({@link Completions#of(String) of}("3"),
* of("7"),
* of("31"),
* of("127"),
* of("8191"),
* of("131071"),
* of("524287"),
* of("2147483647"));
* </pre>
* </blockquote>
*
* A more informative set of completions would include the number
* of each prime:
*
* <blockquote>
* <pre>
* return Arrays.asList({@link Completions#of(String, String) of}("3", "M2"),
* of("7", "M3"),
* of("31", "M5"),
* of("127", "M7"),
* of("8191", "M13"),
* of("131071", "M17"),
* of("524287", "M19"),
* of("2147483647", "M31"));
* </pre>
* </blockquote>
*
* However, if the {@code userText} is available, it can be checked
* to see if only a subset of the Mersenne primes are valid. For
* example, if the user has typed
*
* <blockquote>
* <code>
* @MersennePrime(1
* </code>
* </blockquote>
*
* the value of {@code userText} will be {@code "1"}; and only
* two of the primes are possible completions:
*
* <blockquote>
* <pre>
* return Arrays.asList(of("127", "M7"),
* of("131071", "M17"));
* </pre>
* </blockquote>
*
* Sometimes no valid completion is possible. For example, there
* is no in-range Mersenne prime starting with 9:
*
* <blockquote>
* <code>
* @MersennePrime(9
* </code>
* </blockquote>
*
* An appropriate response in this case is to either return an
* empty list of completions,
*
* <blockquote>
* <pre>
* return Collections.emptyList();
* </pre>
* </blockquote>
*
* or a single empty completion with a helpful message
*
* <blockquote>
* <pre>
* return Arrays.asList(of("", "No in-range Mersenne primes start with 9"));
* </pre>
* </blockquote>
*
* @param element the element being annotated
* @param annotation the (perhaps partial) annotation being
* applied to the element
* @param member the annotation member to return possible completions for
* @param userText source code text to be completed
*
* @return suggested completions to the annotation
*/
Iterable<? extends Completion> getCompletions(Element element,
AnnotationMirror annotation,
ExecutableElement member,
String userText);
}