/*
 * Copyright 2015 Google Inc. All Rights Reserved.
 *
 * 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.errorprone.bugpatterns;

import static com.google.errorprone.BugPattern.Category.JDK;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import static com.google.errorprone.matchers.Description.NO_MATCH;

import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.util.ASTHelpers;
import com.sun.source.tree.AnnotationTree;
import com.sun.source.tree.MethodTree;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import javax.lang.model.type.TypeKind;

/** @author cushon@google.com (Liam Miller-Cushon) */
@BugPattern(
  name = "NullableVoid",
  summary =
      "void-returning methods should not be annotated with @Nullable,"
          + " since they cannot return null",
  explanation = "void-returning methods cannot return null.",
  category = JDK,
  severity = WARNING
)
public class NullableVoid extends BugChecker implements MethodTreeMatcher {

  @Override
  public Description matchMethod(MethodTree tree, VisitorState state) {
    MethodSymbol sym = ASTHelpers.getSymbol(tree);
    if (sym == null) {
      return NO_MATCH;
    }
    if (sym.getReturnType().getKind() != TypeKind.VOID) {
      return NO_MATCH;
    }
    AnnotationTree annotation =
        ASTHelpers.getAnnotationWithSimpleName(tree.getModifiers().getAnnotations(), "Nullable");
    if (annotation == null) {
      return NO_MATCH;
    }
    return describeMatch(annotation, SuggestedFix.delete(annotation));
  }
}