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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.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");

  /**
   * Return whether the given node represents a GETPROP with a first child THIS inside a named
   * class.
   */
  static boolean isThisPropInsideClassWithName(Node maybeGetProp) {
    return getClassNameOfThisProp(maybeGetProp) != null;
  }

  /**
   * Return the fully qualified name of a this.property inside a constructor. This method called
   * should only be called if `isThisPropInsideClassWithName` returns true.
   */
  static String getFullyQualifiedNameOfThisProp(Node getProp) {
    checkArgument(isThisPropInsideClassWithName(getProp));
    String className = 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 = getMemberFunctionClassName(function);
    if (isNullOrEmpty(className)) {
      return null;
    }
    return className;
  }

  /**
   * Return whether the given node represents a MEMBER_FIELD_DEF that is inside a class with a name.
   */
  static boolean isMemberFieldDefInsideClassWithName(Node fieldNode) {
    return getMemberFieldDefClassName(fieldNode) != null;
  }

  /**
   * Return the fully qualified name of a MEMBER_FIELD_DEF. It is invalid to call this method for a
   * field that belongs to a nameless class.
   */
  static String getFullyQualifiedNameOfMemberFieldDef(Node fieldNode) {
    checkArgument(isMemberFieldDefInsideClassWithName(fieldNode));
    String className = getMemberFieldDefClassName(fieldNode);
    return fieldNode.isStaticMember()
        ? className + "." + fieldNode.getString()
        : className + ".prototype." + fieldNode.getString();
  }

  private static @Nullable String getMemberFieldDefClassName(Node fieldNode) {
    checkArgument(fieldNode.isMemberFieldDef());
    Node classNode = fieldNode.getGrandparent();
    checkState(classNode.isClass());
    return NodeUtil.getName(classNode);
  }

  static String getFullyQualifiedNameOfMethod(Node function) {
    checkArgument(isClassMethod(function));
    String className = getMemberFunctionClassName(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 getMemberFunctionClassName(functionNode) != null;
  }

  private static String getMemberFunctionClassName(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();
  }
}