framework/src/main/java/org/checkerframework/framework/util/typeinference/constraint/FIsAReducer.java

package org.checkerframework.framework.util.typeinference.constraint;

import java.util.List;
import java.util.Set;
import javax.lang.model.type.TypeKind;
import org.checkerframework.framework.type.AnnotatedTypeFactory;
import org.checkerframework.framework.type.AnnotatedTypeMirror;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedArrayType;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedDeclaredType;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedIntersectionType;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedNullType;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedPrimitiveType;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedTypeVariable;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedUnionType;
import org.checkerframework.framework.type.AnnotatedTypeMirror.AnnotatedWildcardType;
import org.checkerframework.framework.type.visitor.AbstractAtmComboVisitor;
import org.checkerframework.framework.util.AnnotatedTypes;
import org.plumelib.util.StringsPlume;

/**
 * FIsAReducer takes an FIsA constraint that is not irreducible (@see AFConstraint.isIrreducible)
 * and reduces it by one step. The resulting constraint may still be reducible.
 *
 * <p>Generally reductions should map to corresponding rules in
 * https://docs.oracle.com/javase/specs/jls/se11/html/jls-15.html#jls-15.12.2.7
 */
public class FIsAReducer implements AFReducer {

  protected final FIsAReducingVisitor visitor;
  private final AnnotatedTypeFactory typeFactory;

  public FIsAReducer(final AnnotatedTypeFactory typeFactory) {
    this.typeFactory = typeFactory;
    this.visitor = new FIsAReducingVisitor();
  }

  @Override
  public boolean reduce(AFConstraint constraint, Set<AFConstraint> newConstraints) {
    if (constraint instanceof FIsA) {
      final FIsA fIsA = (FIsA) constraint;
      visitor.visit(fIsA.formalParameter, fIsA.argument, newConstraints);
      return true;

    } else {
      return false;
    }
  }

  /**
   * Given an FIsA constraint of the form: FIsA( typeFromFormalParameter, typeFromMethodArgument )
   *
   * <p>FIsAReducingVisitor visits the constraint as follows: visit ( typeFromFormalParameter,
   * typeFromMethodArgument, newConstraints )
   *
   * <p>The visit method will determine if the given constraint should either:
   *
   * <ul>
   *   <li>be discarded -- in this case, the visitor just returns
   *   <li>reduced to a simpler constraint or set of constraints -- in this case, the new constraint
   *       or set of constraints is added to newConstraints
   * </ul>
   *
   * From the JLS, in general there are 2 rules that govern F = A constraints: If F = Tj, then the
   * constraint Tj = A is implied. If F = U[], where the type U involves Tj, then if A is an array
   * type V[], or a type variable with an upper bound that is an array type V[], where V is a
   * reference type, this algorithm is applied recursively to the constraint {@code V >> U}.
   * Otherwise, no constraint is implied on Tj.
   *
   * <p>Since both F and A may have component types this visitor delves into their components and
   * applies these rules to the components. However, only one step is taken at a time (i.e. this is
   * not a scanner)
   */
  private class FIsAReducingVisitor extends AbstractAtmComboVisitor<Void, Set<AFConstraint>> {
    @Override
    protected String defaultErrorMessage(
        AnnotatedTypeMirror argument,
        AnnotatedTypeMirror parameter,
        Set<AFConstraint> afConstraints) {
      return StringsPlume.joinLines(
          "Unexpected FIsA Combination:",
          "argument=" + argument,
          "parameter=" + parameter,
          "constraints=[",
          StringsPlume.join(", ", afConstraints),
          "]");
    }
    // ------------------------------------------------------------------------
    // Arrays as arguments

    @Override
    public Void visitArray_Array(
        AnnotatedArrayType parameter, AnnotatedArrayType argument, Set<AFConstraint> constraints) {
      constraints.add(new FIsA(parameter.getComponentType(), argument.getComponentType()));
      return null;
    }

    @Override
    public Void visitArray_Declared(
        AnnotatedArrayType parameter,
        AnnotatedDeclaredType argument,
        Set<AFConstraint> constraints) {
      return null;
    }

    @Override
    public Void visitArray_Null(
        AnnotatedArrayType parameter, AnnotatedNullType argument, Set<AFConstraint> constraints) {
      return null;
    }

    @Override
    public Void visitArray_Wildcard(
        AnnotatedArrayType parameter,
        AnnotatedWildcardType argument,
        Set<AFConstraint> constraints) {
      constraints.add(new FIsA(parameter, argument.getExtendsBound()));
      return null;
    }

    // ------------------------------------------------------------------------
    // Declared as argument
    @Override
    public Void visitDeclared_Array(
        AnnotatedDeclaredType parameter,
        AnnotatedArrayType argument,
        Set<AFConstraint> constraints) {
      // should this be Array<String> - T[] the new A2F(String, T)
      return null;
    }

    @Override
    public Void visitDeclared_Declared(
        AnnotatedDeclaredType parameter,
        AnnotatedDeclaredType argument,
        Set<AFConstraint> constraints) {
      if (argument.wasRaw() || parameter.wasRaw()) {
        return null;
      }

      AnnotatedDeclaredType argumentAsParam =
          AnnotatedTypes.castedAsSuper(typeFactory, argument, parameter);
      if (argumentAsParam == null) {
        return null;
      }

      final List<AnnotatedTypeMirror> argTypeArgs = argumentAsParam.getTypeArguments();
      final List<AnnotatedTypeMirror> paramTypeArgs = parameter.getTypeArguments();
      for (int i = 0; i < argTypeArgs.size(); i++) {
        final AnnotatedTypeMirror argTypeArg = argTypeArgs.get(i);
        final AnnotatedTypeMirror paramTypeArg = paramTypeArgs.get(i);

        if (paramTypeArg.getKind() == TypeKind.WILDCARD) {
          final AnnotatedWildcardType paramWc = (AnnotatedWildcardType) paramTypeArg;

          if (argTypeArg.getKind() == TypeKind.WILDCARD) {
            final AnnotatedWildcardType argWc = (AnnotatedWildcardType) argTypeArg;
            constraints.add(new FIsA(paramWc.getExtendsBound(), argWc.getExtendsBound()));
            constraints.add(new FIsA(paramWc.getSuperBound(), argWc.getSuperBound()));
          }

        } else {
          constraints.add(new FIsA(paramTypeArgs.get(i), argTypeArgs.get(i)));
        }
      }

      return null;
    }

    @Override
    public Void visitDeclared_Null(
        AnnotatedDeclaredType parameter,
        AnnotatedNullType argument,
        Set<AFConstraint> constraints) {
      return null;
    }

    @Override
    public Void visitDeclared_Primitive(
        AnnotatedDeclaredType parameter,
        AnnotatedPrimitiveType argument,
        Set<AFConstraint> constraints) {
      return null;
    }

    @Override
    public Void visitDeclared_Union(
        AnnotatedDeclaredType parameter,
        AnnotatedUnionType argument,
        Set<AFConstraint> constraints) {
      return null; // TODO: NOT SUPPORTED AT THE MOMENT
    }

    @Override
    public Void visitIntersection_Intersection(
        AnnotatedIntersectionType parameter,
        AnnotatedIntersectionType argument,
        Set<AFConstraint> constraints) {
      return null; // TODO: NOT SUPPORTED AT THE MOMENT
    }

    @Override
    public Void visitIntersection_Null(
        AnnotatedIntersectionType parameter,
        AnnotatedNullType argument,
        Set<AFConstraint> constraints) {
      return null;
    }

    @Override
    public Void visitNull_Null(
        AnnotatedNullType parameter, AnnotatedNullType argument, Set<AFConstraint> afConstraints) {
      // we sometimes get these when we have captured types passed as arguments
      // regardless they don't give any information
      return null;
    }

    // ------------------------------------------------------------------------
    // Primitive as argument
    @Override
    public Void visitPrimitive_Declared(
        AnnotatedPrimitiveType parameter,
        AnnotatedDeclaredType argument,
        Set<AFConstraint> constraints) {
      // we may be able to eliminate this case, since I believe the corresponding constraint
      // will just be discarded as the parameter must be a boxed primitive
      constraints.add(new FIsA(typeFactory.getBoxedType(parameter), argument));
      return null;
    }

    @Override
    public Void visitPrimitive_Primitive(
        AnnotatedPrimitiveType parameter,
        AnnotatedPrimitiveType argument,
        Set<AFConstraint> constraints) {
      return null;
    }

    @Override
    public Void visitTypevar_Typevar(
        AnnotatedTypeVariable parameter,
        AnnotatedTypeVariable argument,
        Set<AFConstraint> constraints) {
      // if we've reached this point and the two are corresponding type variables, then they
      // are NOT ones that may have a type variable we are inferring types for and therefore
      // we can discard this constraint
      return null;
    }

    @Override
    public Void visitTypevar_Null(
        AnnotatedTypeVariable argument,
        AnnotatedNullType parameter,
        Set<AFConstraint> constraints) {
      return null;
    }
  }
}