src/main/java/com/google/devtools/build/lib/analysis/config/StarlarkDefinedConfigTransition.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.analysis.config;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.skylarkbuildapi.config.ConfigurationTransitionApi;
import com.google.devtools.build.lib.skylarkinterface.SkylarkPrinter;
import com.google.devtools.build.lib.syntax.BaseFunction;
import com.google.devtools.build.lib.syntax.Environment;
import com.google.devtools.build.lib.syntax.EvalException;
import com.google.devtools.build.lib.syntax.Mutability;
import com.google.devtools.build.lib.syntax.SkylarkDict;
import com.google.devtools.build.lib.syntax.SkylarkSemantics;
import java.util.List;
import java.util.Map;

/**
 * Implementation of {@link ConfigurationTransitionApi}.
 *
 * <p>Represents a configuration transition across a dependency edge defined in Starlark.
 */
public abstract class StarlarkDefinedConfigTransition implements ConfigurationTransitionApi {

  private final List<String> inputs;
  private final List<String> outputs;
  private final Location location;

  private StarlarkDefinedConfigTransition(
      List<String> inputs, List<String> outputs, Location location) {
    this.inputs = inputs;
    this.outputs = outputs;
    this.location = location;
  }

  /**
   * Returns true if this transition is for analysis testing. If true, then only attributes of rules
   * with {@code analysis_test=true} may use this transition object.
   */
  public abstract Boolean isForAnalysisTesting();

  /**
   * Returns the input option keys for this transition. Only option keys contained in this
   * list will be provided in the 'settings' argument given to the transition implementation
   * function.
   */
  public List<String> getInputs() {
    return inputs;
  }

  /**
   * Returns the output option keys for this transition. The transition implementation function
   * must return a dictionary where the option keys exactly match the elements of this list.
   */
  public List<String> getOutputs() {
    return outputs;
  }

  /**
   * Returns the location of the Starlark code responsible for determining the transition's changed
   * settings for purposes of error reporting.
   */
  public Location getLocationForErrorReporting() {
    return location;
  }

  /**
   * Given a map of a subset of the "previous" build settings, returns the changed build settings as
   * a result of applying this transition.
   *
   * @param previousSettings a map representing the previous build settings
   * @return a list of changed build setting maps; each element of the list represents a different
   *     child configuration (split transitions will have multiple elements in this list, other
   *     transitions should have a single element). Each build setting map is a map from build
   *     setting to target setting value; all other build settings will remain unchanged
   * @throws EvalException if there is an error evaluating the transition
   * @throws InterruptedException if evaluating the transition is interrupted
   */
  public abstract ImmutableList<Map<String, Object>> getChangedSettings(
      Map<String, Object> previousSettings) throws EvalException, InterruptedException;

  public static StarlarkDefinedConfigTransition newRegularTransition(
      BaseFunction impl,
      List<String> inputs,
      List<String> outputs,
      SkylarkSemantics semantics,
      EventHandler eventHandler) {
    return new RegularTransition(impl, inputs, outputs, semantics, eventHandler);
  }

  public static StarlarkDefinedConfigTransition newAnalysisTestTransition(
      Map<String, Object> changedSettings, Location location) {
    return new AnalysisTestTransition(changedSettings, location);
  }

  private static class AnalysisTestTransition extends StarlarkDefinedConfigTransition {
    private final Map<String, Object> changedSettings;

    public AnalysisTestTransition(Map<String, Object> changedSettings, Location location) {
      super(ImmutableList.of(), ImmutableList.copyOf(changedSettings.keySet()), location);
      this.changedSettings = changedSettings;
    }

    @Override
    public Boolean isForAnalysisTesting() {
      return true;
    }

    @Override
    public ImmutableList<Map<String, Object>> getChangedSettings(
        Map<String, Object> previousSettings) {
      return ImmutableList.of(changedSettings);
    }

    @Override
    public void repr(SkylarkPrinter printer) {
      printer.append("<analysis_test_transition object>");
    }
  }

  private static class RegularTransition extends StarlarkDefinedConfigTransition {
    private final BaseFunction impl;
    private final SkylarkSemantics semantics;
    private final EventHandler eventHandler;

    public RegularTransition(
        BaseFunction impl,
        List<String> inputs,
        List<String> outputs,
        SkylarkSemantics semantics,
        EventHandler eventHandler) {
      super(inputs, outputs, impl.getLocation());
      this.impl = impl;
      this.semantics = semantics;
      this.eventHandler = eventHandler;
    }

    @Override
    public Boolean isForAnalysisTesting() {
      return false;
    }

    @Override
    public ImmutableList<Map<String, Object>> getChangedSettings(
        Map<String, Object> previousSettings) throws EvalException, InterruptedException {
      Object result;
      try {
        result = evalFunction(impl, previousSettings);
      } catch (EvalException e) {
        throw new EvalException(impl.getLocation(), e.getMessage());
      }

      if (!(result instanceof SkylarkDict<?, ?>)) {
        throw new EvalException(
            impl.getLocation(), "Transition function must return a dictionary.");
      }

      // The result is either:
      // 1. a dictionary mapping option name to new option value (for a single transition), or
      // 2. a dictionary of such dictionaries (for a split transition).
      //
      // First try to parse the result as a dictionary of option dictionaries; then try it as an
      // option dictionary.
      SkylarkDict<?, ?> dictOrDictOfDict = (SkylarkDict<?, ?>) result;

      try {
        Map<String, SkylarkDict> dictOfDict =
            dictOrDictOfDict.getContents(
                String.class, SkylarkDict.class, "dictionary of option dictionaries");

        ImmutableList.Builder<Map<String, Object>> builder = ImmutableList.builder();
        for (Map.Entry<String, SkylarkDict> entry : dictOfDict.entrySet()) {
          Map<String, Object> dict =
              entry.getValue().getContents(String.class, Object.class, "an option dictionary");
          builder.add(dict);
        }
        return builder.build();
      } catch (EvalException e) {
        // Fall through.
      }

      Map<String, Object> dict;
      try {
        dict = dictOrDictOfDict.getContents(String.class, Object.class, "an option dictionary");
      } catch (EvalException e) {
        throw new EvalException(impl.getLocation(), e.getMessage());
      }

      return ImmutableList.of(dict);
    }

    @Override
    public void repr(SkylarkPrinter printer) {
      printer.append("<transition object>");
    }

    /** Evaluate the input function with the given argument, and return the return value. */
    private Object evalFunction(BaseFunction function, Object arg)
        throws InterruptedException, EvalException {
      try (Mutability mutability = Mutability.create("eval_transition_function")) {
        Environment env =
            Environment.builder(mutability)
                .setSemantics(semantics)
                .setEventHandler(eventHandler)
                .build();

        return function.call(ImmutableList.of(arg), ImmutableMap.of(), null, env);
      }
    }
  }
}