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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 2004 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.checkArgument;
import static com.google.common.base.Preconditions.checkState;

import com.google.javascript.rhino.Node;
import org.jspecify.nullness.Nullable;

/**
 * Scope contains information about a variable scope in JavaScript. Scopes can be nested, a scope
 * points back to its parent scope. A Scope contains information about variables defined in that
 * scope.
 *
 * @see NodeTraversal
 */
public final class Scope extends AbstractScope {

  private final @Nullable Scope parent;
  private final int depth;

  static Scope createGlobalScope(Node rootNode) {
    return new Scope(rootNode);
  }

  static Scope createChildScope(Scope parent, Node rootNode) {
    return new Scope(parent, rootNode);
  }

  private Scope(Scope parent, Node rootNode) {
    super(rootNode);
    checkChildScope(parent);
    this.parent = parent;
    this.depth = parent.getDepth() + 1;
  }

  private Scope(Node rootNode) {
    super(rootNode);
    checkRootScope();
    this.parent = null;
    this.depth = 0;
  }

  @Override
  public Scope untyped() {
    return this;
  }

  @Override
  public int getDepth() {
    return depth;
  }

  @Override
  public Scope getParent() {
    return parent;
  }

  /**
   * Declares a variable.
   *
   * @param name name of the variable
   * @param nameNode the NAME node declaring the variable
   * @param input the input in which this variable is defined.
   */
  Var declare(String name, Node nameNode, CompilerInput input) {
    checkArgument(!name.isEmpty());
    // Make sure that it's declared only once
    checkState(getOwnSlot(name) == null);
    Var var =
        new Var(
            name,
            nameNode,
            this,
            getVarCount(),
            input,
            /* implicitGoogNamespaceDefinition= */ null);
    declareInternal(name, var);
    return var;
  }

  /**
   * Declares an implicit goog.provide or goog.module namespace in this scope
   *
   * @param name name of the variable
   * @param definition the STRINGLIT node holding the full namespace
   */
  Var declareImplicitGoogNamespaceIfAbsent(String name, Node definition) {
    checkArgument(!name.isEmpty());
    checkState(this.isGlobal(), "Cannot declare implicit goog namespace in local scope %s", this);
    // Allow redeclarations of provides, since they are implicit and don't have a single
    // declaration site.
    Var var = getOwnSlot(name);
    if (var == null) {
      var = Var.createImplicitGoogNamespace(name, this, definition);
      declareInternal(name, var);
    } else if (var.isImplicitGoogNamespace()) {
      var.addImplicitGoogNamespaceDefinition(definition);
    }
    return var;
  }

  @Override
  Var makeImplicitVar(ImplicitVar var) {
    return new Var(
        var.name,
        /* nameNode= */ null,
        this,
        /* index= */ -1,
        /* input= */ null,
        /* implicitGoogNamespaceDefinition= */ null);
  }
}