1 files changed, 27 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/IosApplication.java b/src/main/java/com/google/devtools/build/lib/rules/objc/IosApplication.java
index e23af613bd..f57e53a4b6 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/IosApplication.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/IosApplication.java
@@ -14,7 +14,10 @@
 
 package com.google.devtools.build.lib.rules.objc;
 
+import com.google.common.base.Predicate;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
 import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
@@ -23,6 +26,7 @@ import com.google.devtools.build.lib.analysis.config.BuildOptions;
 import com.google.devtools.build.lib.packages.Attribute.SplitTransition;
 import com.google.devtools.build.lib.rules.apple.AppleConfiguration;
 import com.google.devtools.build.lib.rules.apple.Platform;
+import com.google.devtools.build.lib.rules.objc.ObjcProvider.Flag;
 import com.google.devtools.build.lib.rules.objc.ReleaseBundlingSupport.SplitArchTransition;
 import com.google.devtools.build.lib.rules.objc.ReleaseBundlingSupport.SplitArchTransition.ConfigurationDistinguisher;
 
@@ -48,6 +52,29 @@ public class IosApplication extends ReleaseBundlingTargetFactory {
     super(ReleaseBundlingSupport.APP_BUNDLE_DIR_FORMAT, XcodeProductType.APPLICATION,
         DEPENDENCY_ATTRIBUTES, ConfigurationDistinguisher.IOS_APPLICATION);
   }
+  
+  /**
+   * Validates that there is exactly one watch extension for each OS version.
+   */
+  @Override
+  protected void validateAttributes(RuleContext ruleContext) {
+    Iterable<ObjcProvider> extensionProviders = ruleContext.getPrerequisites(
+        "extensions", Mode.TARGET, ObjcProvider.class);
+    if (hasMoreThanOneWatchExtension(extensionProviders, Flag.HAS_WATCH1_EXTENSION)) {
+      ruleContext.attributeError("extensions", "An iOS application can contain exactly one "
+          + "watch extension for each watch OS version");
+    }
+  }
+  
+  private boolean hasMoreThanOneWatchExtension(Iterable<ObjcProvider> objcProviders,
+      final Flag watchExtensionVersionFlag) {
+    return Lists.newArrayList(Iterables.filter(objcProviders, new Predicate<ObjcProvider>() {
+      @Override
+      public boolean apply(ObjcProvider objcProvider) {
+        return objcProvider.is(watchExtensionVersionFlag);
+      }
+    })).size() > 1;
+  }
 
   @Override
   protected void configureTarget(RuleConfiguredTargetBuilder target, RuleContext ruleContext,