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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 2011 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 com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.StaticSymbolTable;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.SimpleReference;
import com.google.javascript.rhino.jstype.SimpleSlot;
import com.google.javascript.rhino.jstype.StaticTypedScope;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import org.jspecify.nullness.Nullable;

/**
 * A symbol table for references that are removed by preprocessor passes (like {@code
 * ProcessClosurePrimitives}).
 */
final class PreprocessorSymbolTable
    implements StaticTypedScope, StaticSymbolTable {

  /**
   * All preprocessor symbols are globals.
   */
  private final Map symbols = new LinkedHashMap<>();

  private final Multimap refs =
      ArrayListMultimap.create();

  private final Node root;

  PreprocessorSymbolTable(Node root) {
    this.root = root;
  }

  @Override
  public Node getRootNode() {
    return root;
  }

  @Override
  public @Nullable JSType getTypeOfThis() {
    return null;
  }

  @Override
  public @Nullable StaticTypedScope getParentScope() {
    return null;
  }

  @Override
  public SimpleSlot getSlot(String name) {
    return symbols.get(name);
  }

  @Override
  public SimpleSlot getOwnSlot(String name) {
    return getSlot(name);
  }

  @Override
  public Iterable getReferences(SimpleSlot symbol) {
    return Collections.unmodifiableCollection(refs.get(symbol.getName()));
  }

  @Override
  public Iterable getAllSymbols() {
    return Collections.unmodifiableCollection(symbols.values());
  }

  @Override
  public StaticTypedScope getScope(SimpleSlot slot) {
    return this;
  }

  void addReference(Node node) {
    addReference(node, getQualifiedName(node));
  }

  void addReference(Node node, String name) {
    checkNotNull(name);

    symbols.computeIfAbsent(name, (String k) -> new SimpleSlot(k, null, true));

    refs.put(name, new Reference(symbols.get(name), node));
  }

  /**
   * This variant of Node#getQualifiedName is adds special support STRING nodes which represent
   * module names.
   */
  public String getQualifiedName(Node n) {
    return n.isStringLit() ? n.getString() : n.getQualifiedName();
  }

  static final class Reference extends SimpleReference {
    Reference(SimpleSlot symbol, Node node) {
      super(symbol, node);
    }
  }

  /**
   * Object that maybe contains instance of the table. This object is needed because
   * PreprocessorSymbolTable is used by multiple passes in different parts of code which initialized
   * at different times (some even before compiler object is created). Instead instance of factory
   * is passed around. Each pass that uses PreprocessorSymbolTable has to call maybeInitialize()
   * before getting instance.
   */
  public static class CachedInstanceFactory {

    private @Nullable PreprocessorSymbolTable instance;

    public void maybeInitialize(AbstractCompiler compiler) {
      if (compiler.getOptions().preservesDetailedSourceInfo()) {
        Node root = compiler.getRoot();
        if (instance == null || instance.getRootNode() != root) {
          instance = new PreprocessorSymbolTable(root);
        }
      }
    }

    public @Nullable PreprocessorSymbolTable getInstanceOrNull() {
      return instance;
    }
  }
}