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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. 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.

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/*
 * Copyright 2014 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.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.JSTypeNative;
import com.google.javascript.rhino.jstype.JSTypeRegistry;

/** Replaces the ES7 `**` and `**=` operators to calls to `Math.pow`. */
public final class Es7RewriteExponentialOperator
    implements NodeTraversal.Callback, HotSwapCompilerPass {

  private static final FeatureSet transpiledFeatures =
      FeatureSet.BARE_MINIMUM.with(Feature.EXPONENT_OP);

  private final AbstractCompiler compiler;
  private final Node mathPowCall; // This node should only ever be cloned, not directly inserted.

  private final JSType numberType;
  private final JSType stringType;
  private final JSType mathType;
  private final JSType mathPowType;

  public Es7RewriteExponentialOperator(AbstractCompiler compiler) {
    this.compiler = compiler;

    if (compiler.hasTypeCheckingRun()) {
      JSTypeRegistry registry = compiler.getTypeRegistry();
      this.numberType = registry.getNativeType(JSTypeNative.NUMBER_TYPE);
      this.stringType = registry.getNativeType(JSTypeNative.STRING_TYPE);
      // TODO(nickreid): Get the actual type of the `Math` object here in case optimizations care.
      this.mathType = registry.getNativeType(JSTypeNative.UNKNOWN_TYPE);
      this.mathPowType = registry.createFunctionType(numberType, numberType, numberType);
    } else {
      this.numberType = null;
      this.stringType = null;
      this.mathType = null;
      this.mathPowType = null;
    }

    this.mathPowCall = createMathPowCall();
  }

  @Override
  public void process(Node externs, Node root) {
    TranspilationPasses.processTranspile(compiler, externs, transpiledFeatures, this);
    TranspilationPasses.processTranspile(compiler, root, transpiledFeatures, this);
    TranspilationPasses.maybeMarkFeaturesAsTranspiledAway(compiler, transpiledFeatures);
  }

  @Override
  public void hotSwapScript(Node scriptRoot, Node originalRoot) {
    TranspilationPasses.hotSwapTranspile(compiler, scriptRoot, transpiledFeatures, this);
    TranspilationPasses.maybeMarkFeaturesAsTranspiledAway(compiler, transpiledFeatures);
  }

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

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case EXPONENT:
        visitExponentiationOperator(n);
        break;
      case ASSIGN_EXPONENT:
        visitExponentiationAssignmentOperator(n);
        break;
      default:
        break;
    }
  }

  private void visitExponentiationOperator(Node operator) {
    Node callClone = mathPowCall.cloneTree();
    callClone.addChildToBack(operator.removeFirstChild()); // Base argument.
    callClone.addChildToBack(operator.removeFirstChild()); // Exponent argument.

    callClone.useSourceInfoIfMissingFromForTree(operator);
    operator.replaceWith(callClone);

    compiler.reportChangeToEnclosingScope(callClone);
  }

  private void visitExponentiationAssignmentOperator(Node operator) {
    Node lValue = operator.removeFirstChild();

    Node callClone = mathPowCall.cloneTree();
    callClone.addChildToBack(lValue.cloneTree()); // Base argument.
    callClone.addChildToBack(operator.removeFirstChild()); // Exponent argument.

    Node assignment = IR.assign(lValue, callClone).setJSType(numberType);

    assignment.useSourceInfoIfMissingFromForTree(operator);
    operator.replaceWith(assignment);

    compiler.reportChangeToEnclosingScope(assignment);
  }

  private Node createMathPowCall() {
    return IR.call(
            IR.getprop(
                    IR.name("Math").setJSType(mathType), // Force wrapping.
                    IR.string("pow").setJSType(stringType))
                .setJSType(mathPowType))
        .setJSType(numberType);
  }
}