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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.ijs;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Strings.isNullOrEmpty;

import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.QualifiedName;
import org.jspecify.nullness.Nullable;

/**
 * Static utility methods for dealing with classes.  The primary benefit is for papering over
 * the differences between ES6 class and goog.defineClass syntax.
 */
final class ClassUtil {
  private ClassUtil() {}

  private static final QualifiedName GOOG_DEFINECLASS = QualifiedName.of("goog.defineClass");

  static boolean isThisProp(Node getprop) {
    return getClassNameOfThisProp(getprop) != null;
  }

  static String getPrototypeNameOfThisProp(Node getprop) {
    String className = checkNotNull(getClassNameOfThisProp(getprop));
    return className + ".prototype." + getprop.getString();
  }

  private static @Nullable String getClassNameOfThisProp(Node getprop) {
    if (!getprop.isGetProp() || !getprop.getFirstChild().isThis()) {
      return null;
    }
    Node function = NodeUtil.getEnclosingFunction(getprop);
    if (function == null) {
      return null;
    }
    String className = getClassName(function);
    if (isNullOrEmpty(className)) {
      return null;
    }
    return className;
  }

  static String getFullyQualifiedNameOfMethod(Node function) {
    checkArgument(isClassMethod(function));
    String className = getClassName(function);
    checkState(className != null && !className.isEmpty());
    Node memberFunctionDef = function.getParent();
    String methodName = memberFunctionDef.getString();
    return memberFunctionDef.isStaticMember()
        ? className + "." + methodName
        : className + ".prototype." + methodName;
  }

  static boolean isClassMethod(Node functionNode) {
    checkArgument(functionNode.isFunction());
    Node parent = functionNode.getParent();
    if (parent.isMemberFunctionDef()
        && parent.getParent().isClassMembers()) {
      // ES6 class
      return true;
    }
    // goog.defineClass
    return parent.isStringKey()
        && parent.getParent().isObjectLit()
        && parent.getGrandparent().isCall()
        && GOOG_DEFINECLASS.matches(parent.getGrandparent().getFirstChild());
  }

  /**
   * Checks whether the given constructor/member function belongs to a named class, as
   * opposed to an anonymous class.
   */
  static boolean hasNamedClass(Node functionNode) {
    checkArgument(functionNode.isFunction());
    return getClassName(functionNode) != null;
  }

  private static String getClassName(Node functionNode) {
    checkArgument(functionNode.isFunction());
    if (isClassMethod(functionNode)) {
      Node parent = functionNode.getParent();
      if (parent.isMemberFunctionDef()) {
        // ES6 class
        Node classNode = functionNode.getGrandparent().getParent();
        checkState(classNode.isClass());
        return NodeUtil.getName(classNode);
      }
      // goog.defineClass
      checkState(parent.isStringKey());
      Node defineClassCall = parent.getGrandparent();
      checkState(defineClassCall.isCall());
      return NodeUtil.getBestLValue(defineClassCall).getQualifiedName();
    }
    return NodeUtil.getName(functionNode);
  }

  static boolean isConstructor(Node functionNode) {
    if (isClassMethod(functionNode)) {
      return NodeUtil.isEs6Constructor(functionNode)
          ||
          // TODO(b/124020008): Delete this case when `goog.defineClass` is dropped.
          "constructor".equals(functionNode.getParent().getString());
    }
    JSDocInfo jsdoc = NodeUtil.getBestJSDocInfo(functionNode);
    return jsdoc != null && jsdoc.isConstructorOrInterface();
  }
}