Expose ConfigFeatureFlagProvider to skylark

This will be used to create thin skylark rules to allow for select() on provider values, with xcode_config_alias's XcodeProperties to be the first.
This is demonstrated in XcodeConfigTest.

RELNOTES: None.
PiperOrigin-RevId: 167204266

2 files changed, 27 insertions, 3 deletions

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 647c284106..e76a34e67c 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
@@ -15,6 +15,7 @@ java_library(
         "//src/main/java/com/google/devtools/build/lib:build-configuration-option-details",
         "//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:events",
         "//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",
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
index 588ef283a3..80b122c711 100644
--- 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
@@ -15,15 +15,19 @@
 package com.google.devtools.build.lib.rules.config;
 
 import com.google.common.base.Predicate;
+import com.google.common.base.Predicates;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.analysis.TransitiveInfoCollection;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.events.Location;
 import com.google.devtools.build.lib.packages.NativeInfo;
 import com.google.devtools.build.lib.packages.NativeProvider;
 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.syntax.EvalException;
+import java.util.Map;
 
 /** Provider for exporting value and valid value predicate of feature flags to consuming targets. */
 @SkylarkModule(
@@ -37,9 +41,7 @@ public class ConfigFeatureFlagProvider extends NativeInfo {
   static final String SKYLARK_NAME = "FeatureFlagInfo";
 
   /** Skylark constructor and identifier for ConfigFeatureFlagProvider. */
-  static final NativeProvider<ConfigFeatureFlagProvider> SKYLARK_CONSTRUCTOR =
-      new NativeProvider<ConfigFeatureFlagProvider>(
-          ConfigFeatureFlagProvider.class, SKYLARK_NAME) {};
+  static final NativeProvider<ConfigFeatureFlagProvider> SKYLARK_CONSTRUCTOR = new Constructor();
 
   private final String value;
   private final Predicate<String> validityPredicate;
@@ -56,6 +58,27 @@ public class ConfigFeatureFlagProvider extends NativeInfo {
     return new ConfigFeatureFlagProvider(value, isValidValue);
   }
 
+  /** A constructor callable from Skylark for OutputGroupProvider. */
+  private static class Constructor extends NativeProvider<ConfigFeatureFlagProvider> {
+
+    private Constructor() {
+      super(ConfigFeatureFlagProvider.class, SKYLARK_NAME);
+    }
+
+    @Override
+    protected ConfigFeatureFlagProvider createInstanceFromSkylark(Object[] args, Location loc)
+        throws EvalException {
+
+      @SuppressWarnings("unchecked")
+      Map<String, Object> kwargs = (Map<String, Object>) args[0];
+
+      if (!kwargs.containsKey("value") || !(kwargs.get("value") instanceof String)) {
+        throw new EvalException(loc, "FeatureFlagInfo requires 'value' to be set to a string");
+      }
+      return create((String) kwargs.get("value"), Predicates.alwaysTrue());
+    }
+}
+
   public static SkylarkProviderIdentifier id() {
     return SKYLARK_CONSTRUCTOR.id();
   }