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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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/*
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Bob Jervis
 *   Google Inc.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

/**
 * For functions with function(this: T, ...) and T as arguments, type inference
 * will set the type of this on a function literal argument to the actual type
 * of T.
 *
 */
package com.google.javascript.rhino.jstype;

import static com.google.javascript.jscomp.base.JSCompObjects.identical;

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

/** A placeholder type, used as keys in {@link TemplateTypeMap}s. */
public final class TemplateType extends ProxyObjectType {
  private static final JSTypeClass TYPE_CLASS = JSTypeClass.TEMPLATE;

  private final String name;
  private JSType bound;
  private final Node typeTransformation;

  TemplateType(JSTypeRegistry registry, String name) {
    this(registry, name, null, null);
  }

  TemplateType(JSTypeRegistry registry, String name, JSType bound) {
    this(registry, name, bound, null);
  }

  TemplateType(JSTypeRegistry registry, String name, Node typeTransformation) {
    this(registry, name, null, typeTransformation);
  }

  private TemplateType(
      JSTypeRegistry registry,
      String name,
      @Nullable JSType bound,
      @Nullable Node typeTransformation) {
    super(
        registry, bound == null ? registry.getNativeObjectType(JSTypeNative.UNKNOWN_TYPE) : bound);
    this.name = name;
    this.bound = bound == null ? registry.getNativeObjectType(JSTypeNative.UNKNOWN_TYPE) : bound;
    this.typeTransformation = typeTransformation;

    registry.getResolver().resolveIfClosed(this, TYPE_CLASS);
  }

  @Override
  JSTypeClass getTypeClass() {
    return TYPE_CLASS;
  }

  @Override
  public String getReferenceName() {
    return name;
  }

  @Override
  void appendTo(TypeStringBuilder sb) {
    if (identical(bound, registry.getNativeObjectType(JSTypeNative.UNKNOWN_TYPE))) {
      // This is an unbound template, don't print it's bound
      sb.append(this.name);
    } else {
      sb.append(this.name).append(" extends ").append(bound);
    }
  }

  @Override
  public TemplateType toMaybeTemplateType() {
    return this;
  }

  @Override
  public boolean hasAnyTemplateTypesInternal() {
    return true;
  }

  @Override
  public  T visit(Visitor visitor) {
    return visitor.caseTemplateType(this);
  }

  @Override  T visit(RelationshipVisitor visitor, JSType that) {
    return visitor.caseTemplateType(this, that);
  }

  public boolean isTypeTransformation() {
    return typeTransformation != null;
  }

  public Node getTypeTransformation() {
    return typeTransformation;
  }

  public JSType getBound() {
    return bound;
  }

  public void setBound(JSType bound) {
    this.bound = bound;
    this.setReferencedType(bound);
  }

  @Override
  public boolean setValidator(Predicate validator) {
    // ProxyObjectType will delegate to the unknown type's setValidator, which we don't want.
    // Some validator functions special-case template types.
    // Note that this.isUnknownType() is still true, so this override only affects validators that
    // treat TemplateTypes differently from a random type for which isUnknownType() is true.
    // (e.g. FunctionTypeBuilder#ExtendedTypeValidator)
    return validator.apply(this);
  }

  /**
   * This function returns whether or not there is a cycle in the reference chain of this type.
   */
  public boolean containsCycle() {
    // By passing in an unreachable type `null` as the target, the visitor will only return if a
    // cycle is found or a terminating type is reached.
    ContainsUpperBoundSuperTypeVisitor typeVisitor = new ContainsUpperBoundSuperTypeVisitor(null);
    return this.visit(typeVisitor) == ContainsUpperBoundSuperTypeVisitor.Result.CYCLE;
  }

  @Override
  int recursionUnsafeHashCode() {
    // Since TemplateType has identity semantics for equality (see EqualityChecker),
    // use identity hash code to avoid spurious hash conflicts
    return System.identityHashCode(this);
  }
}