com.google.javascript.jscomp.RewriteNullishCoalesceOperator 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 2020 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.Supplier;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.Node;

/** Replaces the ES2020 `??` operator with conditional (?:). */
public final class RewriteNullishCoalesceOperator
    implements NodeTraversal.Callback, HotSwapCompilerPass {

  private static final String TEMP_VAR_NAME_PREFIX = "$jscomp$nullish$tmp";
  private static final FeatureSet TRANSPILED_FEATURES =
      FeatureSet.BARE_MINIMUM.with(Feature.NULL_COALESCE_OP);

  private final AbstractCompiler compiler;
  private final AstFactory astFactory;
  private final Supplier uniqueNameIdSuppier;

  public RewriteNullishCoalesceOperator(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.astFactory = compiler.createAstFactory();
    this.uniqueNameIdSuppier = compiler.getUniqueNameIdSupplier();
  }

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

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

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

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (n.isNullishCoalesce()) {
      visitNullishCoalesce(t, n);
      t.reportCodeChange();
    }
  }

  private void visitNullishCoalesce(NodeTraversal t, Node n) {
    // a() ?? b()
    // let temp;
    // (temp = a) != null) : temp ? b()
    String tempVarName = TEMP_VAR_NAME_PREFIX + uniqueNameIdSuppier.get();
    Node enclosingStatement = NodeUtil.getEnclosingStatement(n);
    Node body = enclosingStatement.getParent();

    Node left = n.getFirstChild().detach();
    Node right = n.getLastChild().detach();

    Node let = astFactory.declareSingleLet(tempVarName, left.getJSType());
    Node assignName = astFactory.createName(tempVarName, left.getJSType());
    Node assign = astFactory.createAssign(assignName, left);
    Node ne = astFactory.createNe(assign, astFactory.createNull());
    Node hookName = astFactory.createName(tempVarName, left.getJSType());
    Node hook = astFactory.createHook(ne, hookName, right);

    let.useSourceInfoIfMissingFromForTree(left);
    assignName.useSourceInfoIfMissingFromForTree(left);
    assign.useSourceInfoIfMissingFromForTree(left);
    ne.useSourceInfoIfMissingFromForTree(left);
    hookName.useSourceInfoIfMissingFromForTree(left);

    body.addChildBefore(let, enclosingStatement);
    n.replaceWith(hook);

    NodeUtil.addFeatureToScript(t.getCurrentScript(), Feature.LET_DECLARATIONS, compiler);
    compiler.reportChangeToEnclosingScope(hook);
  }
}