com.google.javascript.jscomp.J2clEqualitySameRewriterPass Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of closure-compiler-linter Show documentation

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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

There is a newer version: v20200830

Show newest version

/*
 * Copyright 2016 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.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.JSType;

/** An optimization pass to re-write J2CL Equality.$same. */
public class J2clEqualitySameRewriterPass extends AbstractPeepholeOptimization {

  private final boolean useTypes;
  private boolean shouldRunJ2clPasses;

  J2clEqualitySameRewriterPass(boolean useTypes) {
    this.useTypes = useTypes;
  }

  @Override
  void beginTraversal(AbstractCompiler compiler) {
    super.beginTraversal(compiler);
    shouldRunJ2clPasses = J2clSourceFileChecker.shouldRunJ2clPasses(compiler);
  }

  @Override
  Node optimizeSubtree(Node node) {
    if (!shouldRunJ2clPasses) {
      return node;
    }

    if (!isEqualitySameCall(node)) {
      return node;
    }

    Node replacement = trySubstituteEqualitySame(node);
    if (replacement != node) {
      replacement = replacement.useSourceInfoIfMissingFrom(node);
      node.replaceWith(replacement);
      reportChangeToEnclosingScope(replacement);
    }
    return replacement;
  }

  private Node trySubstituteEqualitySame(Node callNode) {
    Node firstExpr = callNode.getSecondChild();
    NodeValue firstExprValue = getKnownLiteralValue(firstExpr);
    Node secondExpr = callNode.getLastChild();
    NodeValue secondExprValue = getKnownLiteralValue(secondExpr);

    if (firstExprValue == NodeValue.UNKNOWN && secondExprValue == NodeValue.UNKNOWN) {
      return callNode;
    }

    if (firstExprValue == NodeValue.NULL_OR_UNDEFINED) {
      return rewriteNullCheck(secondExpr, firstExpr);
    }

    if (secondExprValue == NodeValue.NULL_OR_UNDEFINED) {
      return rewriteNullCheck(firstExpr, secondExpr);
    }

    // There is a coercion danger (e.g. 0 == null) but since at least one side is not null, we can
    // safely use === that will not trigger any coercion.
    return rewriteAsStrictEq(firstExpr, secondExpr);
  }

  private Node rewriteNullCheck(Node expr, Node nullExpression) {
    expr.detach();
    nullExpression.detach();
    if (useTypes && canOnlyBeObject(expr)) {
      return IR.not(expr);
    }
    // At least one side is null or undefined so no coercion danger with ==.
    return IR.eq(expr, nullExpression);
  }

  private boolean canOnlyBeObject(Node n) {
    JSType type = n.getJSType();
    if (type == null) {
      return false;
    }
    type = type.restrictByNotNullOrUndefined();
    return !type.isUnknownType() && !type.isEmptyType() && !type.isAllType() && type.isObjectType();
  }

  private Node rewriteAsStrictEq(Node firstExpr, Node secondExpr) {
    firstExpr.detach();
    secondExpr.detach();
    return IR.sheq(firstExpr, secondExpr);
  }

  private enum NodeValue {
    NULL_OR_UNDEFINED,
    NON_NULL,
    UNKNOWN,
  }

  private static NodeValue getKnownLiteralValue(Node n) {
    switch (NodeUtil.getKnownValueType(n)) {
      case VOID:
        return NodeUtil.canBeSideEffected(n) ? NodeValue.UNKNOWN : NodeValue.NULL_OR_UNDEFINED;
      case NULL:
        return NodeValue.NULL_OR_UNDEFINED;

      case NUMBER:
      case STRING:
      case BOOLEAN:
      case OBJECT:
        return NodeValue.NON_NULL;

      case UNDETERMINED:
        return NodeValue.UNKNOWN;
    }
    throw new AssertionError("Unknown ValueType");
  }

  private static boolean isEqualitySameCall(Node node) {
    return node.isCall()
        // Do not optimize if one or both parameters were removed
        && node.hasXChildren(3)
        && isEqualitySameMethodName(node.getFirstChild());
  }

  private static boolean isEqualitySameMethodName(Node fnName) {
    if (!fnName.isQualifiedName()) {
      return false;
    }
    // NOTE: This should be rewritten to use method name + file name of definition site
    // like other J2CL passes, which is more precise.
    String originalQname = fnName.getOriginalQualifiedName();
    return originalQname.endsWith(".$same") && originalQname.contains("Equality");
  }
}