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The Checker Framework enhances Java's type system to make it more powerful and useful. This lets software developers detect and prevent errors in their Java programs. The Checker Framework includes compiler plug-ins ("checkers") that find bugs or verify their absence. It also permits you to write your own compiler plug-ins.

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package org.checkerframework.framework.util.element;

import com.sun.tools.javac.code.Attribute;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.TargetType;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import org.checkerframework.framework.type.AnnotatedTypeFactory;
import org.checkerframework.framework.type.AnnotatedTypeMirror;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedTypeVariable;
import org.checkerframework.framework.util.element.ElementAnnotationUtil.UnexpectedAnnotationLocationException;
import org.checkerframework.javacutil.BugInCF;

/** Applies the annotations present for a method type parameter onto an AnnotatedTypeVariable. */
public class MethodTypeParamApplier extends TypeParamElementAnnotationApplier {

  /** Apply annotations from {@code element} to {@code type}. */
  public static void apply(
      AnnotatedTypeVariable type, Element element, AnnotatedTypeFactory typeFactory)
      throws UnexpectedAnnotationLocationException {
    new MethodTypeParamApplier(type, element, typeFactory).extractAndApply();
  }

  /**
   * Returns true if element represents a type parameter for a method.
   *
   * @param type ignored
   * @param element the element that might be a type parameter for a method
   * @return true if element represents a type parameter for a method
   */
  public static boolean accepts(AnnotatedTypeMirror type, Element element) {
    return element.getKind() == ElementKind.TYPE_PARAMETER
        && element.getEnclosingElement() instanceof Symbol.MethodSymbol;
  }

  private final Symbol.MethodSymbol enclosingMethod;

  MethodTypeParamApplier(
      AnnotatedTypeVariable type, Element element, AnnotatedTypeFactory typeFactory) {
    super(type, element, typeFactory);

    if (!(element.getEnclosingElement() instanceof Symbol.MethodSymbol)) {
      throw new BugInCF(
          "TypeParameter not enclosed by method?  Type( "
              + type
              + " ) "
              + "Element ( "
              + element
              + " ) ");
    }

    enclosingMethod = (Symbol.MethodSymbol) element.getEnclosingElement();
  }

  /**
   * Returns TargetType.METHOD_TYPE_PARAMETER.
   *
   * @return TargetType.METHOD_TYPE_PARAMETER
   */
  @Override
  protected TargetType lowerBoundTarget() {
    return TargetType.METHOD_TYPE_PARAMETER;
  }

  /**
   * Returns TargetType.METHOD_TYPE_PARAMETER_BOUND.
   *
   * @return TargetType.METHOD_TYPE_PARAMETER_BOUND
   */
  @Override
  protected TargetType upperBoundTarget() {
    return TargetType.METHOD_TYPE_PARAMETER_BOUND;
  }

  /**
   * Returns the index of element in the type parameter list of its enclosing method.
   *
   * @return the index of element in the type parameter list of its enclosing method
   */
  @Override
  public int getElementIndex() {
    return enclosingMethod.getTypeParameters().indexOf(element);
  }

  /** The valid targets. */
  private static final TargetType[] validTargets =
      new TargetType[] {
        TargetType.METHOD_RETURN,
        TargetType.METHOD_FORMAL_PARAMETER,
        TargetType.METHOD_RECEIVER,
        TargetType.THROWS,
        TargetType.LOCAL_VARIABLE,
        TargetType.RESOURCE_VARIABLE,
        TargetType.EXCEPTION_PARAMETER,
        TargetType.NEW,
        TargetType.CAST,
        TargetType.INSTANCEOF,
        TargetType.METHOD_INVOCATION_TYPE_ARGUMENT,
        TargetType.CONSTRUCTOR_INVOCATION_TYPE_ARGUMENT,
        TargetType.METHOD_REFERENCE,
        TargetType.CONSTRUCTOR_REFERENCE,
        TargetType.METHOD_REFERENCE_TYPE_ARGUMENT,
        TargetType.CONSTRUCTOR_REFERENCE_TYPE_ARGUMENT,
        // TODO: from generic anonymous classes; remove when
        // we can depend on only seeing classfiles that were
        // generated by a javac that contains a fix for:
        // https://bugs.openjdk.org/browse/JDK-8198945
        TargetType.CLASS_EXTENDS,
        // TODO: Test case from Issue 3277 produces invalid position.
        // Ignore until this javac bug is fixed:
        // https://bugs.openjdk.org/browse/JDK-8233945
        TargetType.UNKNOWN
      };

  @Override
  protected TargetType[] validTargets() {
    return validTargets;
  }

  /**
   * Returns the TypeCompounds (annotations) of the declaring element.
   *
   * @return the TypeCompounds (annotations) of the declaring element
   */
  @Override
  protected Iterable getRawTypeAttributes() {
    return enclosingMethod.getRawTypeAttributes();
  }

  @Override
  protected boolean isAccepted() {
    return accepts(type, element);
  }
}