com.google.javascript.jscomp.ChainCalls Maven / Gradle / Ivy

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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.
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/*
 * 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.javascript.jscomp.ControlFlowGraph.Branch;
import com.google.javascript.jscomp.DefinitionsRemover.Definition;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.NodeTraversal.ScopedCallback;
import com.google.javascript.jscomp.graph.DiGraph.DiGraphEdge;
import com.google.javascript.rhino.Node;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * Chain calls to functions that return this.
 *
 */
class ChainCalls implements CompilerPass {
  private final AbstractCompiler compiler;
  private final Set badFunctionNodes = new HashSet<>();
  private final Set goodFunctionNodes = new HashSet<>();
  private final List callSites = new ArrayList<>();
  private NameBasedDefinitionProvider defFinder;
  private GatherFunctions gatherFunctions = new GatherFunctions();

  ChainCalls(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    defFinder = new NameBasedDefinitionProvider(compiler, false);
    defFinder.process(externs, root);

    NodeTraversal.traverseEs6(compiler, root, new GatherCallSites());

    for (CallSite callSite : callSites) {
      callSite.parent.removeChild(callSite.n);
      callSite.n.removeChild(callSite.callNode);
      callSite.nextGetPropNode.replaceChild(callSite.nextGetPropFirstChildNode,
                                            callSite.callNode);
      compiler.reportCodeChange();
    }
  }

  /**
   * Determines whether a function always returns this.
   */
  private class GatherFunctions implements ScopedCallback {
    @Override
    public void enterScope(NodeTraversal t) {
      ControlFlowGraph cfg = t.getControlFlowGraph();

      for (DiGraphEdge s : cfg.getImplicitReturn().getInEdges()) {
        Node exitNode = s.getSource().getValue();
        if (!exitNode.isReturn() ||
            exitNode.getFirstChild() == null ||
            !exitNode.getFirstChild().isThis()) {
          badFunctionNodes.add(t.getScopeRoot());
          return;
        }
      }

      goodFunctionNodes.add(t.getScopeRoot());
    }

    @Override
    public void exitScope(NodeTraversal t) {
    }

    @Override
    public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n,
                                  Node parent) {
      return true;
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
    }
  }

  private class GatherCallSites extends AbstractPostOrderCallback {
    /**
     * If the function call returns this and the next statement has the same
     * target expression, record the call site.
     */
    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      if (!n.isExprResult()) {
        return;
      }

      Node callNode = n.getFirstChild();
      if (!callNode.isCall()) {
        return;
      }

      Node getPropNode = callNode.getFirstChild();
      if (!getPropNode.isGetProp()) {
        return;
      }

      Node getPropFirstChildNode = getPropNode.getFirstChild();

      Collection definitions =
          defFinder.getDefinitionsReferencedAt(getPropNode);
      if (definitions == null) {
        return;
      }
      for (Definition definition : definitions) {
        Node rValue = definition.getRValue();
        if (rValue == null) {
          return;
        }
        if (badFunctionNodes.contains(rValue)) {
          return;
        }
        if (!goodFunctionNodes.contains(rValue)) {
          new NodeTraversal(compiler, gatherFunctions, new Es6SyntacticScopeCreator(compiler))
              .traverseInnerNode(
                  rValue, rValue.getParent(), t.getClosestHoistScope().getParent());
          if (badFunctionNodes.contains(rValue)) {
            return;
          }
        }
      }

      Node nextNode = n.getNext();
      if (nextNode == null || !nextNode.isExprResult()) {
        return;
      }

      Node nextCallNode = nextNode.getFirstChild();
      if (!nextCallNode.isCall()) {
        return;
      }

      Node nextGetPropNode = nextCallNode.getFirstChild();
      if (!nextGetPropNode.isGetProp()) {
        return;
      }

      Node nextGetPropFirstChildNode = nextGetPropNode.getFirstChild();
      if (!compiler.areNodesEqualForInlining(
              nextGetPropFirstChildNode, getPropFirstChildNode)) {
        return;
      }

      if (NodeUtil.mayEffectMutableState(getPropFirstChildNode)) {
        return;
      }

      // We can't chain immediately as it we wouldn't recognize further
      // opportunities to chain.
      callSites.add(new CallSite(parent, n, callNode, nextGetPropNode,
                                 nextGetPropFirstChildNode));
    }
  }

  /** Records a call site to chain. */
  private static class CallSite {
    final Node parent;
    final Node n;
    final Node callNode;
    final Node nextGetPropNode;
    final Node nextGetPropFirstChildNode;

    CallSite(Node parent, Node n, Node callNode, Node nextGetPropNode,
             Node nextGetPropFirstChildNode) {
      this.parent = parent;
      this.n = n;
      this.callNode = callNode;
      this.nextGetPropNode = nextGetPropNode;
      this.nextGetPropFirstChildNode = nextGetPropFirstChildNode;
    }
  }
}