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A fast dependency injector for Android and Java.
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/*
 * Copyright (C) 2023 The Dagger 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 dagger.internal.codegen.binding;

import static androidx.room.compiler.processing.XElementKt.isMethod;
import static androidx.room.compiler.processing.XElementKt.isVariableElement;
import static dagger.internal.codegen.xprocessing.XAnnotations.getClassName;
import static dagger.internal.codegen.xprocessing.XElements.asMethod;
import static dagger.internal.codegen.xprocessing.XElements.asVariable;

import androidx.room.compiler.processing.XAnnotation;
import androidx.room.compiler.processing.XElement;
import androidx.room.compiler.processing.XNullability;
import androidx.room.compiler.processing.XType;
import com.google.auto.value.AutoValue;
import java.util.Optional;

/**
 * Contains information about the nullability of an element.
 *
 * Note that an element can be nullable if either:
 *
 * 

 *   The element is annotated with {@code Nullable} or
 *   
the associated kotlin type is nullable (i.e. {@code T?} types in Kotlin source).
 * 
 */
@AutoValue
public abstract class Nullability {
  /** A constant that can represent any non-null element. */
  public static final Nullability NOT_NULLABLE = new AutoValue_Nullability(false, Optional.empty());

  public static Nullability of(XElement element) {
    Optional nullableAnnotation = getNullableAnnotation(element);
    boolean isNullable = isKotlinTypeNullable(element) || nullableAnnotation.isPresent();
    return isNullable ? new AutoValue_Nullability(isNullable, nullableAnnotation) : NOT_NULLABLE;
  }

  private static boolean isKotlinTypeNullable(XElement element) {
    if (isMethod(element)) {
      return isKotlinTypeNullable(asMethod(element).getReturnType());
    } else if (isVariableElement(element)) {
      return isKotlinTypeNullable(asVariable(element).getType());
    } else {
      return false;
    }
  }

  private static boolean isKotlinTypeNullable(XType type) {
    return type.getNullability() == XNullability.NULLABLE;
  }

  /** Returns the first type that specifies this' nullability, or empty if none. */
  private static Optional getNullableAnnotation(XElement element) {
    return element.getAllAnnotations().stream()
        .filter(annotation -> getClassName(annotation).simpleName().contentEquals("Nullable"))
        .findFirst();
  }

  public abstract boolean isNullable();

  public abstract Optional nullableAnnotation();

  Nullability() {}
}