/*
 * Copyright 2017-present Facebook, Inc.
 *
 * 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.facebook.buck.rules.coercer;

import com.facebook.buck.core.cell.CellPathResolver;
import com.facebook.buck.core.model.TargetConfiguration;
import com.facebook.buck.io.filesystem.ProjectFilesystem;
import com.facebook.buck.rules.coercer.TypeCoercer.Traversal;
import com.facebook.buck.rules.macros.OutputMacro;
import com.google.common.collect.ImmutableList;
import java.nio.file.Path;

/**
 * Handles '$(output ...)' macro.
 *
 * @see com.facebook.buck.rules.macros.OutputMacroExpander
 */
public class OutputMacroTypeCoercer implements MacroTypeCoercer<OutputMacro> {

  @Override
  public boolean hasElementClass(Class<?>[] types) {
    for (Class<?> type : types) {
      if (type.isAssignableFrom(getOutputClass())) {
        return true;
      }
    }
    return false;
  }

  @Override
  public Class<OutputMacro> getOutputClass() {
    return OutputMacro.class;
  }

  @Override
  public void traverse(CellPathResolver cellRoots, OutputMacro macro, Traversal traversal) {
    traversal.traverse(macro);
  }

  @Override
  public OutputMacro coerce(
      CellPathResolver cellRoots,
      ProjectFilesystem filesystem,
      Path pathRelativeToProjectRoot,
      TargetConfiguration targetConfiguration,
      ImmutableList<String> args)
      throws CoerceFailedException {
    if (args.size() != 1) {
      throw new CoerceFailedException(
          String.format("expected exactly one argument (found %d)", args.size()));
    }
    return OutputMacro.of(args.get(0));
  }
}

@@ -1919,16 +1919,41 @@
 e() != 1
+ %7C%7C args.get(0).isEmpty()
 ) %7B%0A    

Make output macro fail when no arguments supplied