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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 2017 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.rhino.Node;
import com.google.javascript.rhino.Token;
import java.io.Serializable;

/**
 * Represents a section of code that is uninterrupted by control structures (conditional or
 * iterative logic).
 */
final class BasicBlock implements Serializable {

  private final BasicBlock parent;

  private final Node root;

  /** Whether this block denotes a function scope. */
  private final boolean isFunction;

  /** Whether this block denotes a loop. */
  private final boolean isLoop;

  /**
   * Creates a new block.
   *
   * @param parent The containing block.
   * @param root The root node of the block.
   */
  BasicBlock(BasicBlock parent, Node root) {
    this.parent = parent;
    this.root = root;

    this.isFunction = root.isFunction();

    if (root.hasParent()) {
      Token pType = root.getParent().getToken();
      this.isLoop =
          pType == Token.DO
              || pType == Token.WHILE
              || pType == Token.FOR
              || pType == Token.FOR_OF
              || pType == Token.FOR_AWAIT_OF
              || pType == Token.FOR_IN;
    } else {
      this.isLoop = false;
    }
  }

  BasicBlock getParent() {
    return parent;
  }

  /**
   * Determines whether this block is equivalent to the very first block that is created when
   * reference collection traversal enters global scope. Note that when traversing a single script
   * in a hot-swap fashion a new instance of {@code BasicBlock} is created.
   *
   * @return true if this is global scope block.
   */
  boolean isGlobalScopeBlock() {
    return getParent() == null;
  }

  /** Determines whether this block is guaranteed to begin executing before the given block does. */
  boolean provablyExecutesBefore(BasicBlock thatBlock) {
    // If thatBlock is a descendant of this block, and there are no hoisted
    // blocks between them, then this block must start before thatBlock.
    BasicBlock currentBlock;
    for (currentBlock = thatBlock;
        currentBlock != null && currentBlock != this;
        currentBlock = currentBlock.getParent()) {}

    if (currentBlock == this) {
      return true;
    }
    return isGlobalScopeBlock() && thatBlock.isGlobalScopeBlock();
  }

  boolean isFunction() {
    return isFunction;
  }

  boolean isLoop() {
    return isLoop;
  }

  Node getRoot() {
    return root;
  }

  @Override
  public String toString() {
    return "BasicBlock @ " + root;
  }
}