AccessPathNullnessAnalysis.java

/*
 * Copyright 2014 Google Inc. All Rights Reserved.
 *
 * Modifications copyright (C) 2017 Uber Technologies, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.uber.nullaway.dataflow;

import com.google.common.collect.ImmutableList;
import com.google.errorprone.VisitorState;
import com.sun.source.util.TreePath;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.util.Context;
import com.uber.nullaway.Config;
import com.uber.nullaway.Nullness;
import com.uber.nullaway.handlers.Handler;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Optional;
import java.util.Set;
import java.util.function.Predicate;
import javax.annotation.Nullable;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import org.checkerframework.dataflow.cfg.node.MethodInvocationNode;

/**
 * API to our nullness dataflow analysis for access paths.
 *
 * <p>Based on code from Error Prone; see {@link NullnessAnalysis}
 */
public final class AccessPathNullnessAnalysis {

  private static final Context.Key<AccessPathNullnessAnalysis> FIELD_NULLNESS_ANALYSIS_KEY =
      new Context.Key<>();

  private final AccessPathNullnessPropagation nullnessPropagation;

  private final DataFlow dataFlow;

  private static String OPTIONAL_PATH = "java.util.Optional";

  // Use #instance to instantiate
  private AccessPathNullnessAnalysis(
      Predicate<MethodInvocationNode> methodReturnsNonNull,
      Context context,
      Config config,
      Handler handler) {
    this.nullnessPropagation =
        new AccessPathNullnessPropagation(
            Nullness.NONNULL, methodReturnsNonNull, context, config, handler);
    this.dataFlow = new DataFlow(config.assertsEnabled());
  }

  /**
   * @param context Javac context
   * @param methodReturnsNonNull predicate determining whether a method is assumed to return NonNull
   *     value
   * @param config analysis config
   * @return instance of the analysis
   */
  public static AccessPathNullnessAnalysis instance(
      Context context,
      Predicate<MethodInvocationNode> methodReturnsNonNull,
      Config config,
      Handler handler) {
    AccessPathNullnessAnalysis instance = context.get(FIELD_NULLNESS_ANALYSIS_KEY);
    if (instance == null) {
      instance = new AccessPathNullnessAnalysis(methodReturnsNonNull, context, config, handler);
      context.put(FIELD_NULLNESS_ANALYSIS_KEY, instance);
    }
    return instance;
  }

  /**
   * @param exprPath tree path of expression
   * @param context Javac context
   * @return nullness info for expression, from dataflow
   */
  @Nullable
  public Nullness getNullness(TreePath exprPath, Context context) {
    return dataFlow.expressionDataflow(exprPath, context, nullnessPropagation);
  }

  /**
   * @param path tree path of method, or initializer block
   * @param context Javac context
   * @return fields guaranteed to be nonnull at exit of method (or initializer block)
   */
  public Set<Element> getNonnullFieldsOfReceiverAtExit(TreePath path, Context context) {
    NullnessStore nullnessResult = dataFlow.finalResult(path, context, nullnessPropagation);
    if (nullnessResult == null) {
      // this case can occur if the method always throws an exception
      // be conservative and say nothing is initialized
      return Collections.emptySet();
    }
    return getNonnullReceiverFields(nullnessResult);
  }

  private Set<Element> getNonnullReceiverFields(NullnessStore nullnessResult) {
    Set<AccessPath> nonnullAccessPaths = nullnessResult.getAccessPathsWithValue(Nullness.NONNULL);
    Set<Element> result = new LinkedHashSet<>();
    for (AccessPath ap : nonnullAccessPaths) {
      if (ap.getRoot().isReceiver()) {
        ImmutableList<Element> elements = ap.getElements();
        if (elements.size() == 1) {
          Element elem = elements.get(0);
          if (elem.getKind().equals(ElementKind.FIELD)) {
            result.add(elem);
          }
        }
      }
    }
    return result;
  }

  /**
   * @param path tree path of some expression
   * @param context Javac context
   * @return fields of receiver guaranteed to be nonnull before expression is evaluated
   */
  public Set<Element> getNonnullFieldsOfReceiverBefore(TreePath path, Context context) {
    NullnessStore store = dataFlow.resultBeforeExpr(path, context, nullnessPropagation);
    if (store == null) {
      return Collections.emptySet();
    }
    return getNonnullReceiverFields(store);
  }

  /**
   * @param path tree path of some expression
   * @param context Javac context
   * @return static fields guaranteed to be nonnull before expression is evaluated
   */
  public Set<Element> getNonnullStaticFieldsBefore(TreePath path, Context context) {
    NullnessStore store = dataFlow.resultBeforeExpr(path, context, nullnessPropagation);
    if (store == null) {
      return Collections.emptySet();
    }
    return getNonnullStaticFields(store);
  }

  /**
   * Get nullness info for local variables before some node
   *
   * @param path tree path to some AST node within a method / lambda / initializer
   * @param state visitor state
   * @return nullness info for local variables just before the node
   */
  public NullnessStore getLocalVarInfoBefore(TreePath path, VisitorState state) {
    NullnessStore store = dataFlow.resultBefore(path, state.context, nullnessPropagation);
    if (store == null) {
      return NullnessStore.empty();
    }
    return store.filterAccessPaths(
        (ap) -> {
          if (ap.getElements().size() == 0) {
            AccessPath.Root root = ap.getRoot();
            if (!root.isReceiver()) {
              Element e = root.getVarElement();
              return e.getKind().equals(ElementKind.PARAMETER)
                  || e.getKind().equals(ElementKind.LOCAL_VARIABLE);
            }
          }

          // a filter for Optional get() call
          if (ap.getElements().size() == 1) {
            AccessPath.Root root = ap.getRoot();
            if (!root.isReceiver() && (ap.getElements().get(0) instanceof Symbol.MethodSymbol)) {
              final Element e = root.getVarElement();
              final Symbol.MethodSymbol g = (Symbol.MethodSymbol) ap.getElements().get(0);
              final Optional<Type> tbaseType =
                  Optional.ofNullable(state.getTypeFromString(OPTIONAL_PATH))
                      .map(state.getTypes()::erasure);
              return e.getKind().equals(ElementKind.LOCAL_VARIABLE)
                  && g.getSimpleName().toString().equals("get")
                  && g.getParameters().length() == 0
                  && tbaseType.isPresent()
                  && state.getTypes().isSubtype(g.owner.type, tbaseType.get());
            }
          }
          return false;
        });
  }

  /**
   * @param path tree path of static method, or initializer block
   * @param context Javac context
   * @return fields guaranteed to be nonnull at exit of static method (or initializer block)
   */
  public Set<Element> getNonnullStaticFieldsAtExit(TreePath path, Context context) {
    NullnessStore nullnessResult = dataFlow.finalResult(path, context, nullnessPropagation);
    if (nullnessResult == null) {
      // this case can occur if the method always throws an exception
      // be conservative and say nothing is initialized
      return Collections.emptySet();
    }
    return getNonnullStaticFields(nullnessResult);
  }

  private Set<Element> getNonnullStaticFields(NullnessStore nullnessResult) {
    Set<AccessPath> nonnullAccessPaths = nullnessResult.getAccessPathsWithValue(Nullness.NONNULL);
    Set<Element> result = new LinkedHashSet<>();
    for (AccessPath ap : nonnullAccessPaths) {
      assert !ap.getRoot().isReceiver();
      Element varElement = ap.getRoot().getVarElement();
      if (varElement.getKind().equals(ElementKind.FIELD)) {
        result.add(varElement);
      }
    }
    return result;
  }

  /**
   * Forces a run of the access path nullness analysis on the method (or lambda) at the given
   * TreePath.
   *
   * <p>Because of caching, if the analysis has run in the past for this particular path, it might
   * not be re-run. The intended usage of this method is to force an analysis pass and thus the
   * execution of any Handler hooks into the dataflow analysis (such as `onDataflowInitialStore` or
   * `onDataflowVisitX`).
   *
   * @param methodPath tree path of the method (or lambda) to analyze.
   * @param context Javac context
   * @return the final NullnessStore on exit from the method.
   */
  public NullnessStore forceRunOnMethod(TreePath methodPath, Context context) {
    return dataFlow.finalResult(methodPath, context, nullnessPropagation);
  }

  /** invalidate all caches */
  public void invalidateCaches() {
    dataFlow.invalidateCaches();
  }
}