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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 2015 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.newtypes;

import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;

/**
 * Represents a declaration of a javascript type.
 *
 * See {@link #checkValid} for invariants on a declaration's state.
 * In most cases, only one of the instance fields can be non null.
 */
public class Declaration {
  // Type of local, formal, or extern that the declaration refers to
  private JSType simpleType;
  private Typedef typedef;
  private Namespace ns;
  private DeclaredTypeRegistry funScope;
  private boolean isTypeVar;
  private boolean isConstant;

  public Declaration(JSType simpleType, Typedef typedef, Namespace ns,
      DeclaredTypeRegistry funScope, boolean isTypeVar, boolean isConstant) {
    this.simpleType = simpleType;
    this.typedef = typedef;
    this.ns = ns;
    this.funScope = funScope;
    this.isTypeVar = isTypeVar;
    this.isConstant = isConstant;
    checkValid();
  }

  private void checkValid() {
    if (this.simpleType != null) {
      Preconditions.checkState(this.typedef == null);
    }
    if (this.typedef != null) {
      Preconditions.checkState(
          this.simpleType == null && this.ns == null && this.funScope == null);
    }
    if (this.ns != null) {
      // Note: Non-null nominal with null function is allowed,
      // e.g., /** @constructor */ var Bar = Foo;
      Preconditions.checkState(this.typedef == null);
    }
    if (this.funScope != null) {
      Preconditions.checkState(this.typedef == null);
    }
  }

  public JSType getTypeOfSimpleDecl() {
    return this.simpleType;
  }

  public Typedef getTypedef() {
    return this.typedef;
  }

  public EnumType getEnum() {
    return this.ns instanceof EnumType ? ((EnumType) this.ns) : null;
  }

  public DeclaredTypeRegistry getFunctionScope() {
    return this.funScope;
  }

  public RawNominalType getNominal() {
    return this.ns instanceof RawNominalType ? ((RawNominalType) this.ns) : null;
  }

  public boolean isTypeVar() {
    return this.isTypeVar;
  }

  public boolean isConstant() {
    return this.isConstant;
  }

  public Namespace getNamespace() {
    return this.ns;
  }

  public String toString() {
    return MoreObjects.toStringHelper(this).omitNullValues()
        .add("simpleType", this.simpleType)
        .add("typedef", this.typedef)
        .add("namespace", this.ns)
        .add("scope", this.funScope)
        .toString();
  }
}