Add the config_feature_flag rule.

This rule allows users to define flags as part of the Bazel configuration.
These flags will be select-able through a new attribute on config_setting,
and settable through transitions within certain special rules.

This rule is currently not supported by any other rules, not even
config_setting, and its values cannot be set; accordingly, it's not very
useful yet.

RELNOTES: None.

PiperOrigin-RevId: 151746523

8 files changed, 402 insertions, 5 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/BUILD b/src/main/java/com/google/devtools/build/lib/BUILD
index 03aeea9da7..adfc1a2c3c 100644
--- a/src/main/java/com/google/devtools/build/lib/BUILD
+++ b/src/main/java/com/google/devtools/build/lib/BUILD
@@ -613,6 +613,7 @@ java_library(
         "//src/main/java/com/google/devtools/build/lib/rules/apple",
         "//src/main/java/com/google/devtools/build/lib/rules/apple/cpp",
         "//src/main/java/com/google/devtools/build/lib/rules/apple/swift",
+        "//src/main/java/com/google/devtools/build/lib/rules/config",
         "//src/main/java/com/google/devtools/build/lib/rules/cpp",
         "//src/main/java/com/google/devtools/build/lib/rules/cpp/proto:CcProtoLibrary",
         "//src/main/java/com/google/devtools/build/lib/rules/genquery",
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java
index c9ee722f19..5644d4a358 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java
@@ -101,6 +101,9 @@ import com.google.devtools.build.lib.rules.apple.XcodeVersionRule;
 import com.google.devtools.build.lib.rules.apple.cpp.AppleCcToolchainRule;
 import com.google.devtools.build.lib.rules.apple.swift.SwiftCommandLineOptions;
 import com.google.devtools.build.lib.rules.apple.swift.SwiftConfiguration;
+import com.google.devtools.build.lib.rules.config.ConfigFeatureFlagConfiguration;
+import com.google.devtools.build.lib.rules.config.ConfigFeatureFlagRule;
+import com.google.devtools.build.lib.rules.config.ConfigSkylarkCommon;
 import com.google.devtools.build.lib.rules.cpp.CcIncLibraryRule;
 import com.google.devtools.build.lib.rules.cpp.CcToolchainRule;
 import com.google.devtools.build.lib.rules.cpp.CcToolchainSuiteRule;
@@ -279,7 +282,8 @@ public class BazelRuleClassProvider {
     BAZEL_SETUP.init(builder);
     CORE_RULES.init(builder);
     CORE_WORKSPACE_RULES.init(builder);
-    BASIC_RULES.init(builder);
+    GENERIC_RULES.init(builder);
+    CONFIG_RULES.init(builder);
     PLATFORM_RULES.init(builder);
     PROTO_RULES.init(builder);
     SH_RULES.init(builder);
@@ -357,15 +361,12 @@ public class BazelRuleClassProvider {
         }
       };
 
-  public static final RuleSet BASIC_RULES =
+  public static final RuleSet GENERIC_RULES =
       new RuleSet() {
         @Override
         public void init(Builder builder) {
           builder.addRuleDefinition(new EnvironmentRule());
 
-          builder.addRuleDefinition(new ConfigRuleClasses.ConfigBaseRule());
-          builder.addRuleDefinition(new ConfigRuleClasses.ConfigSettingRule());
-
           builder.addRuleDefinition(new AliasRule());
           builder.addRuleDefinition(new BazelFilegroupRule());
           builder.addRuleDefinition(new TestSuiteRule());
@@ -385,6 +386,26 @@ public class BazelRuleClassProvider {
         }
       };
 
+  public static final RuleSet CONFIG_RULES =
+      new RuleSet() {
+        @Override
+        public void init(Builder builder) {
+          builder.addRuleDefinition(new ConfigRuleClasses.ConfigBaseRule());
+          builder.addRuleDefinition(new ConfigRuleClasses.ConfigSettingRule());
+          builder.addConfig(
+              ConfigFeatureFlagConfiguration.Options.class,
+              new ConfigFeatureFlagConfiguration.Loader());
+
+          builder.addRuleDefinition(new ConfigFeatureFlagRule());
+          builder.addSkylarkAccessibleTopLevels("config_common", new ConfigSkylarkCommon());
+        }
+
+        @Override
+        public ImmutableList<RuleSet> requires() {
+          return ImmutableList.of(CORE_RULES);
+        }
+      };
+
   public static final RuleSet CORE_WORKSPACE_RULES =
       new RuleSet() {
         @Override
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/BUILD b/src/main/java/com/google/devtools/build/lib/rules/config/BUILD
index 6e480d9628..459150ab5f 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/config/BUILD
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/BUILD
@@ -12,9 +12,15 @@ java_library(
     ]),
     deps = [
         "//src/main/java/com/google/devtools/build/lib:build-base",
+        "//src/main/java/com/google/devtools/build/lib:collect",
+        "//src/main/java/com/google/devtools/build/lib:concurrent",
+        "//src/main/java/com/google/devtools/build/lib:packages-internal",
+        "//src/main/java/com/google/devtools/build/lib:preconditions",
+        "//src/main/java/com/google/devtools/build/lib:skylarkinterface",
         "//src/main/java/com/google/devtools/build/lib/actions",
         "//src/main/java/com/google/devtools/build/lib/cmdline",
         "//src/main/java/com/google/devtools/common/options",
+        "//third_party:auto_value",
         "//third_party:guava",
         "//third_party:jsr305",
     ],
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlag.java b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlag.java
new file mode 100644
index 0000000000..5b9ddb780e
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlag.java
@@ -0,0 +1,104 @@
+// Copyright 2017 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.devtools.build.lib.collect.nestedset.Order.STABLE_ORDER;
+import static com.google.devtools.build.lib.syntax.Type.STRING;
+import static com.google.devtools.build.lib.syntax.Type.STRING_LIST;
+
+import com.google.common.base.Predicate;
+import com.google.common.base.Predicates;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMultiset;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Multiset;
+import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
+import com.google.devtools.build.lib.analysis.RuleContext;
+import com.google.devtools.build.lib.analysis.RunfilesProvider;
+import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
+import com.google.devtools.build.lib.packages.RuleClass.ConfiguredTargetFactory.RuleErrorException;
+import com.google.devtools.build.lib.rules.RuleConfiguredTargetFactory;
+import com.google.devtools.build.lib.syntax.Printer;
+import java.util.List;
+
+/**
+ * The implementation of the config_feature_flag rule for defining custom flags for Android rules.
+ */
+public class ConfigFeatureFlag implements RuleConfiguredTargetFactory {
+
+  @Override
+  public ConfiguredTarget create(RuleContext ruleContext)
+      throws InterruptedException, RuleErrorException {
+    List<String> specifiedValues = ruleContext.attributes().get("allowed_values", STRING_LIST);
+    ImmutableSet<String> values = ImmutableSet.copyOf(specifiedValues);
+    Predicate<String> isValidValue = Predicates.in(values);
+    if (values.size() != specifiedValues.size()) {
+      ImmutableMultiset<String> groupedValues = ImmutableMultiset.copyOf(specifiedValues);
+      ImmutableList.Builder<String> duplicates = new ImmutableList.Builder<String>();
+      for (Multiset.Entry<String> value : groupedValues.entrySet()) {
+        if (value.getCount() > 1) {
+          duplicates.add(value.getElement());
+        }
+      }
+      ruleContext.attributeError(
+          "allowed_values",
+          "cannot contain duplicates, but contained multiple of "
+              + Printer.repr(duplicates.build(), '\''));
+    }
+
+    String defaultValue = ruleContext.attributes().get("default_value", STRING);
+    if (!isValidValue.apply(defaultValue)) {
+      ruleContext.attributeError(
+          "default_value",
+          "must be one of "
+              + Printer.repr(values.asList(), '\'')
+              + ", but was "
+              + Printer.repr(defaultValue, '\''));
+    }
+
+    if (ruleContext.hasErrors()) {
+      // Don't bother validating the value if the flag was already incorrectly specified without
+      // looking at the value.
+      return null;
+    }
+
+    String value =
+        ruleContext
+            .getFragment(ConfigFeatureFlagConfiguration.class)
+            .getFeatureFlagValue(ruleContext.getOwner())
+            .or(defaultValue);
+
+    if (!isValidValue.apply(value)) {
+      // TODO(mstaib): When configurationError is available, use that instead.
+      ruleContext.ruleError(
+          "value must be one of "
+              + Printer.repr(values.asList(), '\'')
+              + ", but was "
+              + Printer.repr(value, '\''));
+      return null;
+    }
+
+    ConfigFeatureFlagProvider provider = ConfigFeatureFlagProvider.create(value, isValidValue);
+
+    return new RuleConfiguredTargetBuilder(ruleContext)
+        .setFilesToBuild(NestedSetBuilder.<Artifact>emptySet(STABLE_ORDER))
+        .addProvider(RunfilesProvider.class, RunfilesProvider.EMPTY)
+        .addProvider(ConfigFeatureFlagProvider.class, provider)
+        .addNativeDeclaredProvider(provider)
+        .build();
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagProvider.java b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagProvider.java
new file mode 100644
index 0000000000..0a25669615
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagProvider.java
@@ -0,0 +1,98 @@
+// Copyright 2017 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 com.google.auto.value.AutoValue;
+import com.google.common.base.Predicate;
+import com.google.common.collect.ImmutableMap;
+import com.google.devtools.build.lib.analysis.TransitiveInfoCollection;
+import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
+import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.packages.ClassObjectConstructor;
+import com.google.devtools.build.lib.packages.NativeClassObjectConstructor;
+import com.google.devtools.build.lib.packages.SkylarkClassObject;
+import com.google.devtools.build.lib.packages.SkylarkProviderIdentifier;
+import com.google.devtools.build.lib.skylarkinterface.Param;
+import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
+import com.google.devtools.build.lib.skylarkinterface.SkylarkModule;
+import com.google.devtools.build.lib.util.Preconditions;
+
+/** Provider for exporting value and valid value predicate of feature flags to consuming targets. */
+@SkylarkModule(
+  name = "FeatureFlagInfo",
+  doc = "A provider used to access information about config_feature_flag rules."
+)
+@AutoValue
+@Immutable
+public abstract class ConfigFeatureFlagProvider extends SkylarkClassObject
+    implements TransitiveInfoProvider {
+
+  /** Name used in Skylark for accessing ConfigFeatureFlagProvider. */
+  static final String SKYLARK_NAME = "FeatureFlagInfo";
+
+  /** Skylark constructor and identifier for ConfigFeatureFlagProvider. */
+  static final ClassObjectConstructor SKYLARK_CONSTRUCTOR =
+      new NativeClassObjectConstructor(SKYLARK_NAME) {};
+
+  /** Identifier used to retrieve this provider from rules which export it. */
+  private static final SkylarkProviderIdentifier SKYLARK_IDENTIFIER =
+      SkylarkProviderIdentifier.forKey(SKYLARK_CONSTRUCTOR.getKey());
+
+  ConfigFeatureFlagProvider() {
+    super(SKYLARK_CONSTRUCTOR, ImmutableMap.<String, Object>of());
+  }
+
+  /** Creates a new ConfigFeatureFlagProvider with the given value and valid value predicate. */
+  public static ConfigFeatureFlagProvider create(String value, Predicate<String> isValidValue) {
+    return new AutoValue_ConfigFeatureFlagProvider(value, isValidValue);
+  }
+
+  /** Retrieves and casts the provider from the given target. */
+  public static ConfigFeatureFlagProvider fromTarget(TransitiveInfoCollection target) {
+    Object provider = target.get(SKYLARK_IDENTIFIER);
+    if (provider == null) {
+      return null;
+    }
+    Preconditions.checkState(provider instanceof ConfigFeatureFlagProvider);
+    return (ConfigFeatureFlagProvider) provider;
+  }
+
+  /** Gets the current value of the flag in the flag's current configuration. */
+  @SkylarkCallable(
+    name = "value",
+    structField = true,
+    doc = "The value of the flag in the configuration used by the flag rule."
+  )
+  public abstract String getValue();
+
+  /** Returns whether this value is valid for this flag. */
+  @SkylarkCallable(
+    name = "is_valid_value",
+    doc = "The value of the flag in the configuration used by the flag rule.",
+    parameters = {
+      @Param(
+        name = "value",
+        type = String.class,
+        doc = "String, the value to check for validity for this flag."
+      ),
+    }
+  )
+  public boolean isValidValue(String value) {
+    return getIsValidValue().apply(value);
+  }
+
+  /** Gets the predicate which determines valid values for this flag. */
+  abstract Predicate<String> getIsValidValue();
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagRule.java b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagRule.java
new file mode 100644
index 0000000000..3600b496aa
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagRule.java
@@ -0,0 +1,55 @@
+// Copyright 2017 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.devtools.build.lib.packages.Attribute.attr;
+import static com.google.devtools.build.lib.syntax.Type.STRING;
+import static com.google.devtools.build.lib.syntax.Type.STRING_LIST;
+
+import com.google.devtools.build.lib.analysis.BaseRuleClasses;
+import com.google.devtools.build.lib.analysis.RuleDefinition;
+import com.google.devtools.build.lib.analysis.RuleDefinitionEnvironment;
+import com.google.devtools.build.lib.packages.RuleClass;
+
+/** Rule definition for Android's config_feature_flag rule. */
+public final class ConfigFeatureFlagRule implements RuleDefinition {
+
+  @Override
+  public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env) {
+    return builder
+        .setUndocumented(/* It's unusable as yet, as there are no ways to interact with it. */)
+        .requiresConfigurationFragments(ConfigFeatureFlagConfiguration.class)
+        .add(
+            attr("allowed_values", STRING_LIST)
+                .mandatory()
+                .nonEmpty()
+                .orderIndependent()
+                .nonconfigurable("policy decision; this is defining an element of configuration"))
+        .add(
+            attr("default_value", STRING)
+                .mandatory()
+                .nonconfigurable("policy decision; this is defining an element of configuration"))
+        .build();
+  }
+
+  @Override
+  public RuleDefinition.Metadata getMetadata() {
+    return RuleDefinition.Metadata.builder()
+        .name("config_feature_flag")
+        .ancestors(BaseRuleClasses.BaseRule.class)
+        .factoryClass(ConfigFeatureFlag.class)
+        .build();
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagTransitionFactory.java b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagTransitionFactory.java
new file mode 100644
index 0000000000..8f7ab87954
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagTransitionFactory.java
@@ -0,0 +1,75 @@
+// Copyright 2017 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.devtools.build.lib.packages.BuildType.LABEL_KEYED_STRING_DICT;
+
+import com.google.common.collect.ImmutableSortedMap;
+import com.google.devtools.build.lib.analysis.config.BuildOptions;
+import com.google.devtools.build.lib.analysis.config.PatchTransition;
+import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.packages.NonconfigurableAttributeMapper;
+import com.google.devtools.build.lib.packages.Rule;
+import com.google.devtools.build.lib.packages.RuleTransitionFactory;
+import java.util.Map;
+
+/**
+ * Transition factory which allows for setting the values of config_feature_flags below the rule
+ * it is attached to based on one of that rule's attributes.
+ *
+ * <p>Currently, this is only intended for use by android_binary and other Android top-level rules.
+ */
+public class ConfigFeatureFlagTransitionFactory implements RuleTransitionFactory {
+
+  /** Transition which resets the set of flag-value pairs to the map it was constructed with. */
+  private static final class ConfigFeatureFlagValuesTransition implements PatchTransition {
+    private final ImmutableSortedMap<Label, String> flagValues;
+
+    public ConfigFeatureFlagValuesTransition(Map<Label, String> flagValues) {
+      this.flagValues = ImmutableSortedMap.copyOf(flagValues);
+    }
+
+    @Override
+    public BuildOptions apply(BuildOptions options) {
+      BuildOptions result = options.clone();
+      result.get(ConfigFeatureFlagConfiguration.Options.class).replaceFlagValues(flagValues);
+      return result;
+    }
+
+    @Override
+    public boolean defaultsToSelf() {
+      throw new UnsupportedOperationException("supported in dynamic mode only");
+    }
+  }
+
+  private final String attributeName;
+
+  /**
+   * Creates a transition factory which will generate a transition over a given rule which sets
+   * exactly the flag values in the attribute with the given {@code attributeName} of that rule,
+   * unsetting any flag values not listed there.
+   *
+   * <p>This attribute must be a nonconfigurable {@code LABEL_KEYED_STRING_DICT}.
+   */
+  public ConfigFeatureFlagTransitionFactory(String attributeName) {
+    this.attributeName = attributeName;
+  }
+
+  @Override
+  public PatchTransition buildTransitionFor(Rule rule) {
+    return new ConfigFeatureFlagValuesTransition(
+        NonconfigurableAttributeMapper.of(rule).get(attributeName, LABEL_KEYED_STRING_DICT));
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigSkylarkCommon.java b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigSkylarkCommon.java
new file mode 100644
index 0000000000..f464a45537
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigSkylarkCommon.java
@@ -0,0 +1,37 @@
+// Copyright 2017 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 com.google.devtools.build.lib.packages.ClassObjectConstructor;
+import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
+import com.google.devtools.build.lib.skylarkinterface.SkylarkModule;
+
+/**
+ * Skylark namespace used to interact with Blaze's configurability APIs.
+ */
+@SkylarkModule(
+  name = "config_common",
+  doc = "Functions for Skylark to interact with Blaze's configurability APIs."
+)
+public class ConfigSkylarkCommon {
+  @SkylarkCallable(
+    name = ConfigFeatureFlagProvider.SKYLARK_NAME,
+    doc = "The key used to retrieve the provider containing config_feature_flag's value.",
+    structField = true
+  )
+  public ClassObjectConstructor getConfigFeatureFlagProviderConstructor() {
+    return ConfigFeatureFlagProvider.SKYLARK_CONSTRUCTOR;
+  }
+}