// 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.rules.config;

import static com.google.common.collect.ImmutableSortedMap.toImmutableSortedMap;
import static com.google.common.truth.Truth.assertThat;

import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.Iterables;
import com.google.common.collect.Ordering;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.analysis.ConfiguredRuleClassProvider;
import com.google.devtools.build.lib.analysis.ConfiguredTarget;
import com.google.devtools.build.lib.analysis.RuleContext;
import com.google.devtools.build.lib.analysis.actions.FileWriteAction;
import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
import com.google.devtools.build.lib.analysis.configuredtargets.RuleConfiguredTarget.Mode;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.skylark.util.SkylarkTestCase;
import com.google.devtools.build.lib.testutil.TestRuleClassProvider;
import java.util.Map;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/** Tests for manual trimming of feature flags with the transitive_configs attribute. */
@RunWith(JUnit4.class)
public final class FeatureFlagManualTrimmingTest extends SkylarkTestCase {

  @Before
  public void enableManualTrimming() throws Exception {
    useConfiguration("--enforce_transitive_configs_for_config_feature_flag");
  }

  @Override
  protected ConfiguredRuleClassProvider getRuleClassProvider() {
    ConfiguredRuleClassProvider.Builder builder =
        new ConfiguredRuleClassProvider.Builder().addRuleDefinition(new FeatureFlagSetterRule());
    TestRuleClassProvider.addStandardRules(builder);
    return builder.build();
  }

  @Before
  public void setUpFlagReadingRule() throws Exception {
    scratch.file(
        "test/read_flags.bzl",
        "def _read_flags_impl(ctx):",
        "  ctx.actions.write(",
        "    ctx.outputs.flagdict,",
        "    '\\n'.join(['%s:::%s' % (dep.label, dep[config_common.FeatureFlagInfo].value)",
        "                for dep in ctx.attr.flags]))",
        "  return [DefaultInfo(files = depset([ctx.outputs.flagdict]))]",
        "read_flags = rule(",
        "  implementation = _read_flags_impl,",
        "  attrs = {'flags': attr.label_list()},",
        "  outputs = {'flagdict': '%{name}.flags'},",
        ")");
  }

  @Before
  public void setUpHostTransitionRule() throws Exception {
    scratch.file(
        "test/host_transition.bzl",
        "def _host_transition_impl(ctx):",
        "  files = depset(transitive = [src[DefaultInfo].files for src in ctx.attr.srcs])",
        "  return [DefaultInfo(files = files)]",
        "host_transition = rule(",
        "  implementation = _host_transition_impl,",
        "  attrs = {'srcs': attr.label_list(cfg='host')},",
        ")");
  }

  private ImmutableSortedMap<Label, String> getFlagMapFromConfiguration(BuildConfiguration config) {
    return config.getOptions().get(ConfigFeatureFlagOptions.class).getFlagValues();
  }

  private ImmutableSortedMap<Label, String> getFlagValuesFromOutputFile(Artifact flagDict) {
    String fileContents =
        ((FileWriteAction) getActionGraph().getGeneratingAction(flagDict)).getFileContents();
    return Splitter.on('\n')
        .withKeyValueSeparator(":::")
        .split(fileContents)
        .entrySet()
        .stream()
        .collect(
            toImmutableSortedMap(
                Ordering.natural(),
                (entry) -> Label.parseAbsoluteUnchecked(entry.getKey()),
                Map.Entry::getValue));
  }

  @Test
  public void duplicateTargetsCreatedWithTrimmingDisabled() throws Exception {
    useConfiguration("--noenforce_transitive_configs_for_config_feature_flag");
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'left',",
        "    deps = [':common'],",
        "    flag_values = {",
        "        ':different_flag': 'left',",
        "        ':common_flag': 'configured',",
        "    },",
        "    transitive_configs = [':common_flag'],",
        ")",
        "feature_flag_setter(",
        "    name = 'right',",
        "    deps = [':common'],",
        "    flag_values = {",
        "        ':different_flag': 'right',",
        "        ':common_flag': 'configured',",
        "    },",
        "    transitive_configs = [':common_flag'],",
        ")",
        "read_flags(",
        "    name = 'common',",
        "    flags = [':common_flag'],",
        "    transitive_configs = [':common_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'different_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'common_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    Artifact leftFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:left")).toList());
    Artifact rightFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:right")).toList());

    assertThat(leftFlags).isNotEqualTo(rightFlags);
  }

  @Test
  public void featureFlagSetAndInTransitiveConfigs_GetsSetValue() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':trimmed_flag': 'left',",
        "        ':used_flag': 'configured',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'trimmed_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    Artifact targetFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:target")).toList());

    Label usedFlag = Label.parseAbsolute("//test:used_flag", ImmutableMap.of());
    assertThat(getFlagValuesFromOutputFile(targetFlags)).containsEntry(usedFlag, "configured");
  }

  @Test
  public void featureFlagSetButNotInTransitiveConfigs_IsTrimmedOutAndCollapsesDuplicates()
      throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'left',",
        "    deps = [':common'],",
        "    flag_values = {",
        "        ':different_flag': 'left',",
        "        ':common_flag': 'configured',",
        "    },",
        "    transitive_configs = [':common_flag'],",
        ")",
        "feature_flag_setter(",
        "    name = 'right',",
        "    deps = [':common'],",
        "    flag_values = {" ,
        "        ':different_flag': 'right',",
        "        ':common_flag': 'configured',",
        "    },",
        "    transitive_configs = [':common_flag'],",
        ")",
        "read_flags(",
        "    name = 'common',",
        "    flags = [':common_flag'],",
        "    transitive_configs = [':common_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'different_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'common_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    Artifact leftFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:left")).toList());
    Artifact rightFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:right")).toList());

    assertThat(leftFlags).isEqualTo(rightFlags);
    assertThat(leftFlags.getArtifactOwner()).isEqualTo(rightFlags.getArtifactOwner());
  }

  @Test
  public void featureFlagInTransitiveConfigsButNotSet_GetsDefaultValue() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':trimmed_flag': 'left',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'trimmed_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    Artifact targetFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:target")).toList());

    Label usedFlag = Label.parseAbsolute("//test:used_flag", ImmutableMap.of());
    assertThat(getFlagValuesFromOutputFile(targetFlags)).containsEntry(usedFlag, "default");
  }

  @Test
  public void featureFlagInTransitiveConfigsButNotInTransitiveClosure_IsWastefulButDoesNotError()
      throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'left',",
        "    deps = [':common'],",
        "    flag_values = {",
        "        ':different_flag': 'left',",
        "        ':common_flag': 'configured',",
        "    },",
        "    transitive_configs = [':different_flag', ':common_flag'],",
        ")",
        "feature_flag_setter(",
        "    name = 'right',",
        "    deps = [':common'],",
        "    flag_values = {",
        "        ':different_flag': 'right',",
        "        ':common_flag': 'configured',",
        "    },",
        "    transitive_configs = [':different_flag', ':common_flag'],",
        ")",
        "read_flags(",
        "    name = 'common',",
        "    flags = [':common_flag'],",
        "    transitive_configs = [':different_flag', ':common_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'different_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'common_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    Artifact leftFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:left")).toList());
    Artifact rightFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:right")).toList());

    assertThat(leftFlags).isNotEqualTo(rightFlags);
    assertThat(leftFlags.getArtifactOwner()).isNotEqualTo(rightFlags.getArtifactOwner());
  }

  @Test
  public void emptyTransitiveConfigs_EquivalentRegardlessOfFeatureFlags() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'left',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':used_flag': 'left',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "feature_flag_setter(",
        "    name = 'right',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':used_flag': 'right',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    transitive_configs = [],",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")");

    Artifact leftFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:left")).toList());
    Artifact rightFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:right")).toList());
    Artifact directFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:reader")).toList());

    assertThat(leftFlags).isEqualTo(rightFlags);
    assertThat(leftFlags).isEqualTo(directFlags);
  }

  @Test
  public void absentTransitiveConfigs_EquivalentRegardlessOfFeatureFlags() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'left',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':used_flag': 'left',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "feature_flag_setter(",
        "    name = 'right',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':used_flag': 'right',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        // no transitive_configs = equivalent to []
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")");

    Artifact leftFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:left")).toList());
    Artifact rightFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:right")).toList());
    Artifact directFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:reader")).toList());

    assertThat(leftFlags).isEqualTo(rightFlags);
    assertThat(leftFlags).isEqualTo(directFlags);
  }

  @Test
  public void nonexistentLabelInTransitiveConfigs_DoesNotError() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':trimmed_flag': 'left',",
        "    },",
        "    transitive_configs = [':false_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    transitive_configs = [':false_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'trimmed_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")");

    getConfiguredTarget("//test:target");
    assertNoEvents();
  }

  @Test
  public void flagSetBySetterButNotInTransitiveConfigs_CanBeUsedByDeps() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':not_actually_trimmed_flag': 'left',",
        "    },",
        "    transitive_configs = [],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':not_actually_trimmed_flag'],",
        "    transitive_configs = [':not_actually_trimmed_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'not_actually_trimmed_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")");

    getConfiguredTarget("//test:target");
    assertNoEvents();
  }

  @Test
  public void featureFlagInUnusedSelectBranchButNotInTransitiveConfigs_DoesNotError()
      throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':trimmed_flag': 'left',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = select({':used_flag@other': [':trimmed_flag'], '//conditions:default': []}),",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_setting(",
        "    name = 'used_flag@other',",
        "    flag_values = {':used_flag': 'other'},",
        ")",
        "config_feature_flag(",
        "    name = 'trimmed_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    getConfiguredTarget("//test:target");
    assertNoEvents();
  }

  @Test
  public void featureFlagTarget_IsTrimmedToOnlyItself() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    exports_flag = ':read_flag',",
        "    flag_values = {",
        "        ':trimmed_flag': 'left',",
        "        ':read_flag': 'configured',",
        "    },",
        "    transitive_configs = [':trimmed_flag', ':read_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'trimmed_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'read_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    ConfiguredTarget target = getConfiguredTarget("//test:target");
    RuleContext ruleContext = getRuleContext(target);
    BuildConfiguration childConfiguration =
        Iterables.getOnlyElement(ruleContext.getPrerequisiteConfiguredTargetAndTargets("exports_flag", Mode.TARGET)).getConfiguration();

    Label childLabel = Label.parseAbsoluteUnchecked("//test:read_flag");
    assertThat(getFlagMapFromConfiguration(childConfiguration).keySet())
        .containsExactly(childLabel);
  }

  @Test
  public void featureFlagAccessedByPathWithMissingLabel_ProducesError() throws Exception {
    reporter.removeHandler(failFastHandler); // expecting an error
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':broken'],",
        "    flag_values = {",
        "        ':used_flag': 'configured',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "filegroup(",
        "    name = 'broken',",
        "    srcs = [':reader'],",
        "    transitive_configs = [],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    assertThat(getConfiguredTarget("//test:target")).isNull();
    assertContainsEvent(
        "Feature flag //test:used_flag was accessed in a configuration it is not present in. All "
            + "targets which depend on //test:used_flag directly or indirectly must name it in "
            + "their transitive_configs attribute.");
  }

  @Test
  public void featureFlagAccessedByPathWithMissingTransitiveConfigs_ProducesError()
      throws Exception {
    reporter.removeHandler(failFastHandler); // expecting an error
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':broken'],",
        "    flag_values = {",
        "        ':used_flag': 'configured',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "filegroup(",
        "    name = 'broken',",
        "    srcs = [':reader'],",
        // no transitive_configs = equivalent to []
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    assertThat(getConfiguredTarget("//test:target")).isNull();
    assertContainsEvent(
        "Feature flag //test:used_flag was accessed in a configuration it is not present in. All "
            + "targets which depend on //test:used_flag directly or indirectly must name it in "
            + "their transitive_configs attribute.");
  }

  @Test
  public void featureFlagInHostConfiguration_HasDefaultValue() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':host_transition.bzl', 'host_transition')",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':host'],",
        "    flag_values = {",
        "        ':used_flag': 'configured',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "host_transition(",
        "    name = 'host',",
        "    srcs = [':reader'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    Artifact targetFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:target")).toList());

    Label usedFlag = Label.parseAbsolute("//test:used_flag", ImmutableMap.of());
    assertThat(getFlagValuesFromOutputFile(targetFlags)).containsEntry(usedFlag, "default");
  }

  @Test
  public void featureFlagInHostConfiguration_HasNoTransitiveConfigEnforcement() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':host_transition.bzl', 'host_transition')",
        "load(':read_flags.bzl', 'read_flags')",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':host'],",
        "    flag_values = {",
        "        ':used_flag': 'configured',",
        "    },",
        // no transitive_configs
        ")",
        "host_transition(",
        "    name = 'host',",
        "    srcs = [':reader'],",
        // no transitive_configs
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        // no transitive_configs
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    getConfiguredTarget("//test:target");
    assertNoEvents();
  }

  @Test
  public void featureFlagAccessedDirectly_ReturnsDefaultValue() throws Exception {
    scratch.file(
        "test/BUILD",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    assertThat(
            ConfigFeatureFlagProvider.fromTarget(getConfiguredTarget("//test:used_flag"))
                .getFlagValue())
        .isEqualTo("default");
  }

  @Test
  public void featureFlagAccessedViaTopLevelLibraryTarget_ReturnsDefaultValue() throws Exception {
    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");
    Artifact targetFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:reader")).toList());

    Label usedFlag = Label.parseAbsolute("//test:used_flag", ImmutableMap.of());
    assertThat(getFlagValuesFromOutputFile(targetFlags)).containsEntry(usedFlag, "default");
  }

  @Test
  public void featureFlagSettingRules_OverrideFlagsFromReverseTransitiveClosure()
      throws Exception {
    // In other words: if you have a dependency which sets feature flags itself, you don't need to
    // name any of the feature flags used by that target or its transitive closure, as it sets
    // feature flags itself.
    // This is because the feature flag setting transition (which calls replaceFlagValues) runs
    // before the trimming transition and completely replaces the feature flag set. Thus, when
    // the trimming transition (which calls trimFlagValues) runs, its requests are always satisfied.

    scratch.file(
        "test/BUILD",
        "load(':read_flags.bzl', 'read_flags')",
        "filegroup(",
        "    name = 'toplevel',",
        "    srcs = [':target'],",
        // no transitive_configs
        ")",
        "feature_flag_setter(",
        "    name = 'target',",
        "    deps = [':reader'],",
        "    flag_values = {",
        "        ':trimmed_flag': 'left',",
        "        ':used_flag': 'configured',",
        "    },",
        "    transitive_configs = [':used_flag'],",
        ")",
        "read_flags(",
        "    name = 'reader',",
        "    flags = [':used_flag'],",
        "    transitive_configs = [':used_flag'],",
        ")",
        "config_feature_flag(",
        "    name = 'trimmed_flag',",
        "    allowed_values = ['default', 'left', 'right'],",
        "    default_value = 'default',",
        ")",
        "config_feature_flag(",
        "    name = 'used_flag',",
        "    allowed_values = ['default', 'configured', 'other'],",
        "    default_value = 'default',",
        ")");

    Artifact targetFlags =
        Iterables.getOnlyElement(getFilesToBuild(getConfiguredTarget("//test:toplevel")).toList());

    Label usedFlag = Label.parseAbsolute("//test:used_flag", ImmutableMap.of());
    assertThat(getFlagValuesFromOutputFile(targetFlags)).containsEntry(usedFlag, "configured");
  }
}