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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 2021 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 static com.google.common.base.Preconditions.checkNotNull;
import static com.google.javascript.jscomp.AstFactory.type;

import com.google.common.annotations.GwtIncompatible;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;

/**
 * Contains compiler passes to protect `goog.LOCALE` from optimization during the main optimizations
 * phase of compilation, then replace it with the specific destination locale near the end of
 * compilation.
 */
@GwtIncompatible("Unnecessary")
final class LocaleDataPasses {

  private LocaleDataPasses() {}

  // Replacements for values that needed to be protected from optimizations.
  static final String GOOG_LOCALE_REPLACEMENT = "__JSC_LOCALE__";

  static class ProtectGoogLocale implements CompilerPass {
    private final AbstractCompiler compiler;

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

    @Override
    public void process(Node externs, Node root) {
      // Create the extern symbols
      NodeUtil.createSynthesizedExternsSymbol(compiler, GOOG_LOCALE_REPLACEMENT);
      ProtectCurrentLocale protectLocaleCallback = new ProtectCurrentLocale(compiler);
      NodeTraversal.traverse(compiler, root, protectLocaleCallback);
    }
  }

  /** Protect `goog.LOCALE` by replacing it with an extern-defined name. */
  private static class ProtectCurrentLocale extends AbstractPostOrderCallback {
    private final AbstractCompiler compiler;
    private final AstFactory astFactory;

    ProtectCurrentLocale(AbstractCompiler compiler) {
      this.compiler = compiler;
      this.astFactory = compiler.createAstFactory();
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      if (isGoogDotLocaleReference(n)) {
        // We will replace the RHS of `goog.LOCALE = goog.define(...);`, but everywhere
        // else we will replace `goog.LOCALE` itself, so we don't have to waste time
        // inlining it later.
        final Node nodeToReplace = NodeUtil.isLhsOfAssign(n) ? n.getNext() : n;
        Node replacement = astFactory.createName(GOOG_LOCALE_REPLACEMENT, type(nodeToReplace));
        replacement.putBooleanProp(Node.IS_CONSTANT_NAME, true);
        nodeToReplace.replaceWith(replacement);
        compiler.reportChangeToEnclosingScope(parent);
      }
    }
  }

  // matching against an actual Node is faster than matching against the string "goog.LOCALE"
  private static final Node QNAME_FOR_GOOG_LOCALE = IR.getprop(IR.name("goog"), "LOCALE");

  private static boolean isGoogDotLocaleReference(Node n) {
    // NOTE: Theoretically there could be a local variable named `goog`, but it's not worth checking
    // for that.
    return n.matchesQualifiedName(QNAME_FOR_GOOG_LOCALE);
  }

  /** This class replaces `__JSC_LOCALE__` with the actual locale string. */
  static class LocaleSubstitutions extends AbstractPostOrderCallback implements CompilerPass {

    private static final String DEFAULT_LOCALE = "en";
    private final Node qnameForLocale = IR.name(GOOG_LOCALE_REPLACEMENT);

    private final AbstractCompiler compiler;
    private final AstFactory astFactory;
    private final String locale;

    LocaleSubstitutions(AbstractCompiler compiler, String locale) {
      this.compiler = compiler;
      this.astFactory = compiler.createAstFactory();
      // Use the "default" locale if not otherwise set.
      this.locale = locale == null ? DEFAULT_LOCALE : locale;
    }

    @Override
    public void process(Node externs, Node root) {
      // Create the extern symbol
      NodeTraversal.traverse(compiler, root, this);
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      if (n.matchesName(this.qnameForLocale)) {
        Node replacement = astFactory.createString(checkNotNull(locale)).srcref(n);
        n.replaceWith(replacement);
        compiler.reportChangeToEnclosingScope(replacement);
      }
    }
  }
}