// Copyright 2015 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.
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//
//    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,
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package com.google.devtools.build.lib.analysis.constraints;

import com.google.auto.value.AutoValue;
import com.google.devtools.build.lib.analysis.LabelAndLocation;
import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
import com.google.devtools.build.lib.cmdline.Label;

/**
 * A provider that advertises which environments the associated target is compatible with
 * (from the point of view of the constraint enforcement system).
 */
public interface SupportedEnvironmentsProvider extends TransitiveInfoProvider {

  /**
   * Returns the static environments this target is compatible with. Static environments
   * are those that are independent of build configuration (e.g. declared in {@code restricted_to} /
   * {@code compatible_with}). See {@link ConstraintSemantics} for details.
   */
  EnvironmentCollection getStaticEnvironments();

  /**
   * Returns the refined environments this rule is compatible with. Refined environments are
   * static environments with unsupported environments from {@code select}able deps removed (on the
   * principle that others paths in the select would have provided those environments, so this rule
   * is "refined" to match whichever deps got chosen).
   *
   * <p>>Refined environments require knowledge of the build configuration. See
   * {@link ConstraintSemantics} for details.
   */
  EnvironmentCollection getRefinedEnvironments();

  /**
   * Provides all context necessary to communicate which dependencies caused an environment to be
   * refined out of the current rule.
   *
   * <p>The culprit<b>s</b> are actually two rules:
   *
   * <pre>
   *   some_rule(name = "adep", restricted_to = ["//foo:a"])
   *
   *   some_rule(name = "bdep", restricted_to = ["//foo:b"])
   *
   *   some_rule(
   *       name = "has_select",
   *       restricted_to = ["//foo:a", "//foo:b"],
   *       deps = select({
   *         ":acond": [:"adep"],
   *         ":bcond": [:"bdep"],
   *       }
   * </pre>
   *
   * <p>If we build a target with <code>":has_select"</code> somewhere in its deps and trigger
   * <code>":bcond"</code> and that strips <code>"//foo:a"</code> out of the top-level target's
   * environments in a way that triggers an error, the user needs to understand two rules to trace
   * this error. <code>":has_select"</code> is the direct culprit, because this is the first rule
   * that strips <code>"//foo:a"</code>. But it does that because its <code>select()</code> path
   * chooses <code>":bdep"</code>, and <code>":bdep"</code> is why <code>":has_select"</code>
   * decides it's a <code>"//foo:b"</code>-only rule for this build.
   */
  @AutoValue
  abstract class RemovedEnvironmentCulprit {
    public static RemovedEnvironmentCulprit create(LabelAndLocation culprit,
        Label selectedDepForCulprit) {
      return new AutoValue_SupportedEnvironmentsProvider_RemovedEnvironmentCulprit(culprit,
          selectedDepForCulprit);
    }

    public abstract LabelAndLocation culprit();

    public abstract Label selectedDepForCulprit();
  }

  /**
   * If the given environment was refined away from this target's set of supported environments,
   * returns the dependency that originally removed the environment.
   *
   * <p>For example, if the current rule is restricted_to [E] and depends on D1, D1 is restricted_to
   * [E] and depends on D2, and D2 is restricted_to [E, F] and has a select() with one path
   * following an E-restricted dep and the other path following an F-restricted dep, then when the
   * build chooses the F path the current rule has [E] refined to [] and D2 is the culprit.
   *
   * <p>If the given environment was not refined away for this rule, returns null.
   *
   * <p>See {@link ConstraintSemantics} class documentation for more details on refinement.
   */
  RemovedEnvironmentCulprit getRemovedEnvironmentCulprit(Label environment);
}