src/main/java/com/google/devtools/build/lib/starlarkbuildapi/FragmentCollectionApi.java

// Copyright 2018 The Bazel Authors. 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.devtools.build.lib.starlarkbuildapi;

import com.google.common.base.Joiner;
import com.google.devtools.build.docgen.annot.DocCategory;
import javax.annotation.Nullable;
import net.starlark.java.annot.StarlarkBuiltin;
import net.starlark.java.eval.StarlarkValue;
import net.starlark.java.eval.Structure;

/** Represents a collection of configuration fragments in Starlark. */
@StarlarkBuiltin(
    name = "fragments",
    category = DocCategory.BUILTIN,
    doc =
        "A collection of configuration fragments available in the current rule implementation"
            + " context. Access a specific fragment by its field name. For example,"
            + " <code>ctx.fragments.java</code> <p>Only configuration fragments which are declared"
            + " in the rule definition may be accessed in this collection.</p><p>See the <a"
            + " href=\"../fragments.html\">configuration"
            + " fragment reference</a> for a list of available fragments and the <a"
            + " href=\"https://bazel.build/extending/rules#configuration_fragments\">rules"
            + " documentation</a> for how to use them.")
public interface FragmentCollectionApi extends Structure, StarlarkValue {

  @Override
  @Nullable
  default String getErrorMessageForUnknownField(String name) {
    return String.format(
        "There is no configuration fragment named '%s'. Available fragments: %s",
        name, fieldsToString());
  }

  default String fieldsToString() {
    return String.format("'%s'", Joiner.on("', '").join(getFieldNames()));
  }
}