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

1 files changed, 104 insertions, 0 deletions

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();
+  }
+}