checker/src/main/java/org/checkerframework/checker/mustcall/MustCallTransfer.java

package org.checkerframework.checker.mustcall;

import com.sun.source.tree.ClassTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.VariableTree;
import com.sun.source.util.TreePath;
import java.util.List;
import javax.annotation.processing.ProcessingEnvironment;
import javax.lang.model.element.AnnotationMirror;
import javax.lang.model.element.Element;
import javax.lang.model.type.TypeMirror;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.dataflow.analysis.TransferInput;
import org.checkerframework.dataflow.analysis.TransferResult;
import org.checkerframework.dataflow.cfg.node.LocalVariableNode;
import org.checkerframework.dataflow.cfg.node.MethodInvocationNode;
import org.checkerframework.dataflow.cfg.node.Node;
import org.checkerframework.dataflow.cfg.node.ObjectCreationNode;
import org.checkerframework.dataflow.cfg.node.StringConversionNode;
import org.checkerframework.dataflow.cfg.node.TernaryExpressionNode;
import org.checkerframework.dataflow.expression.JavaExpression;
import org.checkerframework.framework.flow.CFAnalysis;
import org.checkerframework.framework.flow.CFStore;
import org.checkerframework.framework.flow.CFTransfer;
import org.checkerframework.framework.flow.CFValue;
import org.checkerframework.javacutil.TreePathUtil;
import org.checkerframework.javacutil.TreeUtils;
import org.checkerframework.javacutil.TypesUtils;
import org.checkerframework.javacutil.trees.TreeBuilder;

/**
 * Transfer function for the must-call type system. Its primary purposes are (1) to create temporary
 * variables for expressions (which allow those expressions to have refined information in the
 * store, which the consistency checker can use), and (2) to reset refined information when a method
 * annotated with @CreatesObligation is called.
 */
public class MustCallTransfer extends CFTransfer {

  /** For building new AST nodes. */
  private final TreeBuilder treeBuilder;

  /** The type factory. */
  private MustCallAnnotatedTypeFactory atypeFactory;

  /**
   * A cache for the default type for java.lang.String, to avoid needing to look it up for every
   * implicit string conversion. See {@link #getDefaultStringType(StringConversionNode)}.
   */
  private @MonotonicNonNull AnnotationMirror defaultStringType;

  /**
   * Create a MustCallTransfer.
   *
   * @param analysis the analysis
   */
  public MustCallTransfer(CFAnalysis analysis) {
    super(analysis);
    atypeFactory = (MustCallAnnotatedTypeFactory) analysis.getTypeFactory();
    ProcessingEnvironment env = atypeFactory.getChecker().getProcessingEnvironment();
    treeBuilder = new TreeBuilder(env);
  }

  @Override
  public TransferResult<CFValue, CFStore> visitStringConversion(
      StringConversionNode n, TransferInput<CFValue, CFStore> p) {
    // Implicit String conversions should assume that the String's type is
    // whatever the default for String is, not that the conversion is polymorphic.
    TransferResult<CFValue, CFStore> result = super.visitStringConversion(n, p);
    LocalVariableNode temp = getOrCreateTempVar(n);
    if (temp != null) {
      AnnotationMirror defaultStringType = getDefaultStringType(n);
      JavaExpression localExp = JavaExpression.fromNode(temp);
      insertIntoStores(result, localExp, defaultStringType);
    }
    return result;
  }

  /**
   * Returns the default type for java.lang.String, which is cached in this class to avoid
   * recomputing it. If the cache is currently unset, this method sets it.
   *
   * @param n a string conversion node, from which the type is computed if it is required
   * @return the type of java.lang.String
   */
  private AnnotationMirror getDefaultStringType(StringConversionNode n) {
    if (this.defaultStringType == null) {
      this.defaultStringType =
          atypeFactory
              .getAnnotatedType(TypesUtils.getTypeElement(n.getType()))
              .getAnnotationInHierarchy(atypeFactory.TOP);
    }
    return this.defaultStringType;
  }

  @Override
  public TransferResult<CFValue, CFStore> visitMethodInvocation(
      MethodInvocationNode n, TransferInput<CFValue, CFStore> in) {
    TransferResult<CFValue, CFStore> result = super.visitMethodInvocation(n, in);

    updateStoreWithTempVar(result, n);
    if (!atypeFactory.getChecker().hasOption(MustCallChecker.NO_ACCUMULATION_FRAMES)) {
      List<JavaExpression> targetExprs =
          CreatesObligationElementSupplier.getCreatesObligationExpressions(
              n, atypeFactory, atypeFactory);
      for (JavaExpression targetExpr : targetExprs) {
        AnnotationMirror defaultType =
            atypeFactory
                .getAnnotatedType(TypesUtils.getTypeElement(targetExpr.getType()))
                .getAnnotationInHierarchy(atypeFactory.TOP);

        if (result.containsTwoStores()) {
          CFStore thenStore = result.getThenStore();
          lubWithStoreValue(thenStore, targetExpr, defaultType);

          CFStore elseStore = result.getElseStore();
          lubWithStoreValue(elseStore, targetExpr, defaultType);
        } else {
          CFStore store = result.getRegularStore();
          lubWithStoreValue(store, targetExpr, defaultType);
        }
      }
    }
    return result;
  }

  /**
   * Computes the LUB of the current value in the store for expr, if it exists, and defaultType.
   * Inserts that LUB into the store as the new value for expr.
   *
   * @param store a CFStore
   * @param expr an expression that might be in the store
   * @param defaultType the default type of the expression's static type
   */
  private void lubWithStoreValue(CFStore store, JavaExpression expr, AnnotationMirror defaultType) {
    CFValue value = store.getValue(expr);
    CFValue defaultTypeAsCFValue =
        analysis.createSingleAnnotationValue(defaultType, expr.getType());
    CFValue newValue = defaultTypeAsCFValue.leastUpperBound(value);
    store.clearValue(expr);
    store.insertValue(expr, newValue);
  }

  @Override
  public TransferResult<CFValue, CFStore> visitObjectCreation(
      ObjectCreationNode node, TransferInput<CFValue, CFStore> input) {
    TransferResult<CFValue, CFStore> result = super.visitObjectCreation(node, input);
    updateStoreWithTempVar(result, node);
    return result;
  }

  @Override
  public TransferResult<CFValue, CFStore> visitTernaryExpression(
      TernaryExpressionNode node, TransferInput<CFValue, CFStore> input) {
    TransferResult<CFValue, CFStore> result = super.visitTernaryExpression(node, input);
    updateStoreWithTempVar(result, node);
    return result;
  }

  /**
   * This method either creates or looks up the temp var t for node, and then updates the store to
   * give t the same type as node.
   *
   * @param node the node to be assigned to a temporary variable
   * @param result the transfer result containing the store to be modified
   */
  public void updateStoreWithTempVar(TransferResult<CFValue, CFStore> result, Node node) {
    // Must-call obligations on primitives are not supported.
    if (!TypesUtils.isPrimitiveOrBoxed(node.getType())) {
      LocalVariableNode temp = getOrCreateTempVar(node);
      if (temp != null) {
        JavaExpression localExp = JavaExpression.fromNode(temp);
        AnnotationMirror anm =
            atypeFactory
                .getAnnotatedType(node.getTree())
                .getAnnotationInHierarchy(atypeFactory.TOP);
        insertIntoStores(result, localExp, anm == null ? atypeFactory.TOP : anm);
      }
    }
  }

  /**
   * Either returns the temporary variable associated with node, or creates one if one does not
   * exist.
   *
   * @param node a node, which must be an expression (not a statement)
   * @return a temporary variable node representing {@code node} that can be placed into a store
   */
  private @Nullable LocalVariableNode getOrCreateTempVar(Node node) {
    LocalVariableNode localVariableNode = atypeFactory.tempVars.get(node.getTree());
    if (localVariableNode == null) {
      VariableTree temp = createTemporaryVar(node);
      if (temp != null) {
        IdentifierTree identifierTree = treeBuilder.buildVariableUse(temp);
        localVariableNode = new LocalVariableNode(identifierTree);
        localVariableNode.setInSource(true);
        atypeFactory.tempVars.put(node.getTree(), localVariableNode);
      }
    }
    return localVariableNode;
  }

  /**
   * Creates a variable declaration for the given expression node, if possible.
   *
   * @param node an expression node
   * @return a variable tree for the node, or null if an appropriate containing element cannot be
   *     located
   */
  protected @Nullable VariableTree createTemporaryVar(Node node) {
    ExpressionTree tree = (ExpressionTree) node.getTree();
    TypeMirror treeType = TreeUtils.typeOf(tree);
    Element enclosingElement;
    TreePath path = atypeFactory.getPath(tree);
    if (path == null) {
      enclosingElement = TreeUtils.elementFromTree(tree).getEnclosingElement();
    } else {
      ClassTree classTree = TreePathUtil.enclosingClass(path);
      enclosingElement = TreeUtils.elementFromTree(classTree);
    }
    if (enclosingElement == null) {
      return null;
    }
    // Declare and initialize a new, unique variable
    VariableTree tmpVarTree =
        treeBuilder.buildVariableDecl(treeType, uniqueName("temp-var"), enclosingElement, tree);
    return tmpVarTree;
  }

  /** A unique identifier counter for node names. */
  protected long uid = 0;

  /**
   * Creates a unique, abitrary string that can be used as a name for a temporary variable, using
   * the given prefix. Can be used up to Long.MAX_VALUE times.
   *
   * @param prefix the prefix for the name
   * @return a unique name that starts with the prefix
   */
  protected String uniqueName(String prefix) {
    return prefix + "-" + uid++;
  }
}