DefinitionUseSiteFinder.java

/*
 * Copyright 2009 The Closure Compiler Authors.
 *
 * 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.google.javascript.jscomp;

import com.google.common.base.Preconditions;
import com.google.common.collect.LinkedHashMultimap;
import com.google.common.collect.Multimap;
import com.google.javascript.jscomp.DefinitionsRemover.Definition;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;
import java.util.Collection;

/**
 * Built on top of the {@link NameBasedDefinitionProvider}, this class additionally collects the
 * use sites for each definition. It is useful for constructing a full reference graph of the entire
 * ast.
 *
 */
// TODO(stalcup): track useSites in lhs of GET_ELEM nodes as well.
public class DefinitionUseSiteFinder extends NameBasedDefinitionProvider {

  private final Multimap<String, UseSite> nameUseSiteMultimap;

  public DefinitionUseSiteFinder(AbstractCompiler compiler) {
    super(compiler, false);
    this.nameUseSiteMultimap = LinkedHashMultimap.create();
  }

  @Override
  public void process(Node externs, Node source) {
    super.process(externs, source);
    NodeTraversal.traverseEs6(
        compiler, source, new UseSiteGatheringCallback());
  }

  /**
   * Returns a collection of use sites that may refer to provided definition. Returns an empty
   * collection if the definition is not used anywhere.
   *
   * @param definition Definition of interest.
   * @return use site collection.
   */
  public Collection<UseSite> getUseSites(Definition definition) {
    Preconditions.checkState(hasProcessBeenRun, "The process was not run");
    String name = getSimplifiedName(definition.getLValue());
    return nameUseSiteMultimap.get(name);
  }

  private class UseSiteGatheringCallback extends AbstractPostOrderCallback {
    @Override
    public void visit(NodeTraversal traversal, Node node, Node parent) {
      if (!node.isGetProp() && !node.isName()) {
        return;
      }

      Collection<Definition> defs = getDefinitionsReferencedAt(node);
      if (defs == null) {
        return;
      }

      Definition first = defs.iterator().next();

      String name = getSimplifiedName(first.getLValue());
      Preconditions.checkNotNull(name);
      nameUseSiteMultimap.put(
          name,
          new UseSite(node, traversal.getScope(), traversal.getModule()));
    }
  }

  /**
   * @param use A use site to check.
   * @return Whether the use is a call or new.
   */
  static boolean isCallOrNewSite(UseSite use) {
    Node call = use.node.getParent();
    if (call == null) {
      // The node has been removed from the AST.
      return false;
    }
    // We need to make sure we're dealing with a call to the function we're
    // optimizing. If the the first child of the parent is not the site, this
    // is a nested call and it's a call to another function.
    return NodeUtil.isCallOrNew(call) && call.getFirstChild() == use.node;
  }

  boolean canModifyDefinition(Definition definition) {
    if (isExported(definition)) {
      return false;
    }

    // Don't modify unused definitions for two reasons:
    // 1) It causes unnecessary churn
    // 2) Other definitions might be used to reflect on this one using
    //    goog.reflect.object (the check for definitions with uses is below).
    Collection<UseSite> useSites = getUseSites(definition);
    if (useSites.isEmpty()) {
      return false;
    }

    for (UseSite site : useSites) {
      // This catches the case where an object literal in goog.reflect.object
      // and a prototype method have the same property name.

      // NOTE(nicksantos): Maps and trogedit both do this by different
      // mechanisms.

      Node nameNode = site.node;
      Collection<Definition> singleSiteDefinitions =
          getDefinitionsReferencedAt(nameNode);
      if (singleSiteDefinitions.size() > 1) {
        return false;
      }

      Preconditions.checkState(!singleSiteDefinitions.isEmpty());
      Preconditions.checkState(singleSiteDefinitions.contains(definition));
    }

    return true;
  }

  /**
   * @return Whether the definition is directly exported.
   */
  private boolean isExported(Definition definition) {
    // Assume an exported method result is used.
    Node lValue = definition.getLValue();
    if (lValue == null) {
      return true;
    }

    String partialName;
    if (lValue.isGetProp()) {
      partialName = lValue.getLastChild().getString();
    } else if (lValue.isName()) {
      partialName = lValue.getString();
    } else {
      // GETELEM is assumed to be an export or other expression are unknown
      // uses.
      return true;
    }

    CodingConvention codingConvention = compiler.getCodingConvention();
    return codingConvention.isExported(partialName);
  }

  /**
   * Traverse a node and its children and remove any references to from
   * the structures.
   */
  void removeReferences(Node node) {
    if (DefinitionsRemover.isDefinitionNode(node)) {
      DefinitionSite defSite = definitionNodeByDefinitionSite.get(node);
      if (defSite != null) {
        Definition def = defSite.definition;
        String name = getSimplifiedName(def.getLValue());
        if (name != null) {
          this.definitionNodeByDefinitionSite.remove(node);
          this.nameDefinitionMultimap.remove(name, def);
        }
      }
    } else {
      Node useSite = node;
      if (useSite.isGetProp()) {
        String propName = useSite.getLastChild().getString();
        if (propName.equals("apply") || propName.equals("call")) {
          useSite = useSite.getFirstChild();
        }
      }
      String name = getSimplifiedName(useSite);
      if (name != null) {
        this.nameUseSiteMultimap.remove(name, new UseSite(useSite, null, null));
      }
    }

    for (Node child : node.children()) {
      removeReferences(child);
    }
  }
}