Generate module maps for each objc_* target with compilation support.

This uses CppModuleMap and CppModuleMapAction to generate clang module maps for the target and its transitive dependencies. To enable this feature, you must pass -experimental_objc_enable_module_maps to bazel.

For objc_* targets that need to use the "modules" language features (@import, Swift interop, etc), set the "enable_modules" attribute to 1.

--
MOS_MIGRATED_REVID=103045673

12 files changed, 457 insertions, 115 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/BinaryLinkingTargetFactory.java b/src/main/java/com/google/devtools/build/lib/rules/objc/BinaryLinkingTargetFactory.java
index 21f4518f6f..9e757e2bdc 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/BinaryLinkingTargetFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/BinaryLinkingTargetFactory.java
@@ -201,6 +201,7 @@ abstract class BinaryLinkingTargetFactory implements RuleConfiguredTargetFactory
                     "non_propagated_deps", Mode.TARGET, ObjcProvider.class))
             .setIntermediateArtifacts(intermediateArtifacts)
             .setAlwayslink(false)
+            .setHasModuleMap()
             .addExtraImportLibraries(ObjcRuleClasses.j2ObjcLibraries(ruleContext))
             .setLinkedBinary(intermediateArtifacts.strippedSingleArchitectureBinary());
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java b/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
index d31e9891fa..f8d41c3b4d 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
@@ -27,6 +27,7 @@ import static com.google.devtools.build.lib.rules.objc.ObjcProvider.IMPORTED_LIB
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.INCLUDE;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.INCLUDE_SYSTEM;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.LIBRARY;
+import static com.google.devtools.build.lib.rules.objc.ObjcProvider.MODULE_MAP;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.SDK_DYLIB;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.SDK_FRAMEWORK;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.WEAK_SDK_FRAMEWORK;
@@ -66,6 +67,8 @@ import com.google.devtools.build.lib.analysis.actions.SpawnAction;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.lib.packages.TargetUtils;
 import com.google.devtools.build.lib.packages.Type;
+import com.google.devtools.build.lib.rules.cpp.CppModuleMap;
+import com.google.devtools.build.lib.rules.cpp.CppModuleMapAction;
 import com.google.devtools.build.lib.rules.cpp.LinkerInputs;
 import com.google.devtools.build.lib.rules.java.J2ObjcConfiguration;
 import com.google.devtools.build.lib.rules.objc.ObjcCommon.CompilationAttributes;
@@ -112,6 +115,17 @@ public final class CompilationSupport {
       };
 
   /**
+   * Predicate to remove '.inc' files from an iterable.
+   */
+  private static final Predicate<Artifact> NON_INC_FILES =
+      new Predicate<Artifact>() {
+        @Override
+        public boolean apply(Artifact artifact) {
+          return !artifact.getFilename().endsWith(".inc");
+        }
+      };
+
+  /**
    * Iterable wrapper providing strong type safety for arguments to binary linking.
    */
   static final class ExtraLinkArgs extends IterableWrapper<String> {
@@ -161,10 +175,20 @@ public final class CompilationSupport {
    */
   CompilationSupport registerCompileAndArchiveActions(ObjcCommon common) {
     if (common.getCompilationArtifacts().isPresent()) {
+      registerGenerateModuleMapAction(common.getCompilationArtifacts());
+      IntermediateArtifacts intermediateArtifacts =
+          ObjcRuleClasses.intermediateArtifacts(ruleContext);
+      Optional<CppModuleMap> moduleMap;
+      if (ObjcRuleClasses.objcConfiguration(ruleContext).moduleMapsEnabled()) {
+        moduleMap = Optional.of(intermediateArtifacts.moduleMap());
+      } else {
+        moduleMap = Optional.<CppModuleMap>absent();
+      }
       registerCompileAndArchiveActions(
           common.getCompilationArtifacts().get(),
-          ObjcRuleClasses.intermediateArtifacts(ruleContext),
+          intermediateArtifacts,
           common.getObjcProvider(),
+          moduleMap,
           ruleContext.getConfiguration().isCodeCoverageEnabled());
     }
     return this;
@@ -174,25 +198,42 @@ public final class CompilationSupport {
    * Creates actions to compile each source file individually, and link all the compiled object
    * files into a single archive library.
    */
-  private void registerCompileAndArchiveActions(CompilationArtifacts compilationArtifacts,
-      IntermediateArtifacts intermediateArtifacts, ObjcProvider objcProvider,
+  private void registerCompileAndArchiveActions(
+      CompilationArtifacts compilationArtifacts,
+      IntermediateArtifacts intermediateArtifacts,
+      ObjcProvider objcProvider,
+      Optional<CppModuleMap> moduleMap,
       boolean isCodeCoverageEnabled) {
     ImmutableList.Builder<Artifact> objFiles = new ImmutableList.Builder<>();
     for (Artifact sourceFile : compilationArtifacts.getSrcs()) {
       Artifact objFile = intermediateArtifacts.objFile(sourceFile);
       objFiles.add(objFile);
       if (ObjcRuleClasses.SWIFT_SOURCES.matches(sourceFile.getFilename())) {
-        registerSwiftCompileAction(sourceFile, objFile, intermediateArtifacts);
+        registerSwiftCompileAction(sourceFile, objFile, intermediateArtifacts, objcProvider);
       } else {
-        registerCompileAction(sourceFile, objFile, objcProvider, intermediateArtifacts,
-            compilationArtifacts, ImmutableList.of("-fobjc-arc"), isCodeCoverageEnabled);
+        registerCompileAction(
+            sourceFile,
+            objFile,
+            objcProvider,
+            moduleMap,
+            intermediateArtifacts,
+            compilationArtifacts,
+            ImmutableList.of("-fobjc-arc"),
+            isCodeCoverageEnabled);
       }
     }
     for (Artifact nonArcSourceFile : compilationArtifacts.getNonArcSrcs()) {
       Artifact objFile = intermediateArtifacts.objFile(nonArcSourceFile);
       objFiles.add(objFile);
-      registerCompileAction(nonArcSourceFile, objFile, objcProvider, intermediateArtifacts,
-          compilationArtifacts, ImmutableList.of("-fno-objc-arc"), isCodeCoverageEnabled);
+      registerCompileAction(
+          nonArcSourceFile,
+          objFile,
+          objcProvider,
+          moduleMap,
+          intermediateArtifacts,
+          compilationArtifacts,
+          ImmutableList.of("-fno-objc-arc"),
+          isCodeCoverageEnabled);
     }
 
     if (compilationArtifacts.hasSwiftSources()) {
@@ -208,6 +249,7 @@ public final class CompilationSupport {
       Artifact sourceFile,
       Artifact objFile,
       ObjcProvider objcProvider,
+      Optional<CppModuleMap> moduleMap,
       IntermediateArtifacts intermediateArtifacts,
       CompilationArtifacts compilationArtifacts,
       Iterable<String> otherFlags,
@@ -259,6 +301,28 @@ public final class CompilationSupport {
         .add("-MD")
         .addExecPath("-MF", dotdFile);
 
+    if (moduleMap.isPresent()) {
+      // -fmodule-map-file only loads the module in Xcode 7, so we add the module maps's directory
+      // to the include path instead.
+      // TODO(bazel-team): Use -fmodule-map-file when Xcode 6 support is dropped.
+      commandLine
+          .add(attributes.enableModules() ? "-fmodules" : "-fmodule-maps")
+          .add("-iquote")
+          .add(
+              moduleMap
+                  .get()
+                  .getArtifact()
+                  .getExecPath()
+                  .getParentDirectory()
+                  .toString())
+          .add("-fmodule-name=" + moduleMap.get().getName());
+      if (attributes.enableModules()) {
+        String cachePath =
+            ruleContext.getConfiguration().getGenfilesFragment() + "/_objc_module_cache";
+        commandLine.add("-fmodules-cache-path=" + cachePath);
+      }
+    }
+
     // TODO(bazel-team): Remote private headers from inputs once they're added to the provider.
     ruleContext.registerAction(ObjcRuleClasses.spawnOnDarwinActionBuilder(ruleContext)
         .setMnemonic("ObjcCompile")
@@ -270,6 +334,7 @@ public final class CompilationSupport {
         .addOutputs(gcnoFiles.build())
         .addOutput(dotdFile)
         .addTransitiveInputs(objcProvider.get(HEADER))
+        .addTransitiveInputs(objcProvider.get(MODULE_MAP))
         .addInputs(compilationArtifacts.getPrivateHdrs())
         .addTransitiveInputs(objcProvider.get(FRAMEWORK_FILE))
         .addInputs(compilationArtifacts.getPchFile().asSet())
@@ -285,7 +350,8 @@ public final class CompilationSupport {
   private void registerSwiftCompileAction(
       Artifact sourceFile,
       Artifact objFile,
-      IntermediateArtifacts intermediateArtifacts) {
+      IntermediateArtifacts intermediateArtifacts,
+      ObjcProvider objcProvider) {
     ObjcConfiguration objcConfiguration = ObjcRuleClasses.objcConfiguration(ruleContext);
 
     // Compiling a single swift file requires knowledge of all of the other
@@ -331,16 +397,27 @@ public final class CompilationSupport {
       inputHeaders.add(bridgingHeader.get());
     }
 
-    ruleContext.registerAction(ObjcRuleClasses.spawnOnDarwinActionBuilder(ruleContext)
-        .setMnemonic("SwiftCompile")
-        .setExecutable(SWIFT)
-        .setCommandLine(commandLine.build())
-        .addInput(sourceFile)
-        .addInputs(otherSwiftSources)
-        .addInputs(inputHeaders.build())
-        .addOutput(objFile)
-        .addOutput(intermediateArtifacts.swiftModuleFile(sourceFile))
-        .build(ruleContext));
+    // Import the Objective-C module map.
+    // TODO(bazel-team): Find a way to import the module map directly, instead of the parent
+    // directory?
+    if (objcConfiguration.moduleMapsEnabled()) {
+      PathFragment moduleMapPath = intermediateArtifacts.moduleMap().getArtifact().getExecPath();
+      commandLine.add("-I").add(moduleMapPath.getParentDirectory().toString());
+    }
+
+    ruleContext.registerAction(
+        ObjcRuleClasses.spawnOnDarwinActionBuilder(ruleContext)
+            .setMnemonic("SwiftCompile")
+            .setExecutable(SWIFT)
+            .setCommandLine(commandLine.build())
+            .addInput(sourceFile)
+            .addInputs(otherSwiftSources)
+            .addInputs(inputHeaders.build())
+            .addTransitiveInputs(objcProvider.get(HEADER))
+            .addTransitiveInputs(objcProvider.get(MODULE_MAP))
+            .addOutput(objFile)
+            .addOutput(intermediateArtifacts.swiftModuleFile(sourceFile))
+            .build(ruleContext));
   }
 
   /**
@@ -459,6 +536,53 @@ public final class CompilationSupport {
     return this;
   }
 
+  /**
+   * Registers an action that will generate a clang module map for this target, using the hdrs
+   * attribute of this rule.
+   */
+  public CompilationSupport registerGenerateModuleMapAction(
+      Optional<CompilationArtifacts> compilationArtifacts) {
+    if (ObjcRuleClasses.objcConfiguration(ruleContext).moduleMapsEnabled()) {
+      Iterable<Artifact> publicHeaders = attributes.hdrs();
+      Iterable<Artifact> privateHeaders = ImmutableList.<Artifact>of();
+      if (compilationArtifacts.isPresent()) {
+        CompilationArtifacts artifacts = compilationArtifacts.get();
+        publicHeaders = Iterables.concat(publicHeaders, artifacts.getAdditionalHdrs());
+        privateHeaders = Iterables.concat(privateHeaders, artifacts.getPrivateHdrs());
+      }
+      CppModuleMap moduleMap = ObjcRuleClasses.intermediateArtifacts(ruleContext).moduleMap();
+      registerGenerateModuleMapAction(moduleMap, publicHeaders, privateHeaders);
+    }
+    return this;
+  }
+
+  /**
+   * Registers an action that will generate a clang module map.
+   *
+   * @param moduleMap the module map to generate
+   * @param publicHeaders the headers that should be directly accessible by dependers
+   * @param privateHeaders the headers that should only be directly accessible by this module
+   */
+  private void registerGenerateModuleMapAction(
+      CppModuleMap moduleMap, Iterable<Artifact> publicHeaders, Iterable<Artifact> privateHeaders) {
+    // The current clang (clang-600.0.57) on Darwin doesn't support 'textual', so we can't have
+    // '.inc' files in the module map (since they're implictly textual).
+    // TODO(bazel-team): Remove filtering once clang-700 is the base clang we support.
+    publicHeaders = Iterables.filter(publicHeaders, NON_INC_FILES);
+    privateHeaders = Iterables.filter(privateHeaders, NON_INC_FILES);
+    ruleContext.registerAction(
+        new CppModuleMapAction(
+            ruleContext.getActionOwner(),
+            moduleMap,
+            privateHeaders,
+            publicHeaders,
+            attributes.moduleMapsForDirectDeps(),
+            ImmutableList.<PathFragment>of(),
+            /*compiledModule=*/ true,
+            /*moduleMapHomeIsCwd=*/ false,
+            /*generateSubModules=*/ true));
+  }
+
   private void registerLinkAction(ObjcProvider objcProvider, ExtraLinkArgs extraLinkArgs,
       Iterable<Artifact> extraLinkInputs, Optional<Artifact> dsymBundle) {
     ObjcConfiguration objcConfiguration = ObjcRuleClasses.objcConfiguration(ruleContext);
@@ -688,7 +812,22 @@ public final class CompilationSupport {
             .setIntermediateArtifacts(intermediateArtifacts)
             .setPchFile(Optional.<Artifact>absent())
             .build();
-        registerCompileAndArchiveActions(compilationArtifact, intermediateArtifacts, objcProvider,
+        // The module map that the above intermediateArtifacts would point to is a combination of
+        // the current target and the java target. Instead, we want the one generated for that
+        // source, but there is no easy way to get that. So for now, compile the source with the
+        // module map (and therefore module name) for this rule.
+        // TODO(bazel-team): Generate module maps along with the J2Objc sources, and use that here.
+        Optional<CppModuleMap> moduleMap;
+        if (ObjcRuleClasses.objcConfiguration(ruleContext).moduleMapsEnabled()) {
+          moduleMap = Optional.of(ObjcRuleClasses.intermediateArtifacts(ruleContext).moduleMap());
+        } else {
+          moduleMap = Optional.<CppModuleMap>absent();
+        }
+        registerCompileAndArchiveActions(
+            compilationArtifact,
+            intermediateArtifacts,
+            objcProvider,
+            moduleMap,
             ruleContext.getConfiguration().isCodeCoverageEnabled());
       }
     }
@@ -696,6 +835,24 @@ public final class CompilationSupport {
     return this;
   }
 
+  /**
+   * Registers actions that generates a module map for all {@link J2ObjcSource}s in
+   * {@link J2ObjcSrcsProvider}.
+   *
+   * @return this compilation support
+   */
+  public CompilationSupport registerJ2ObjcGenerateModuleMapAction(J2ObjcSrcsProvider provider) {
+    if (ObjcRuleClasses.objcConfiguration(ruleContext).moduleMapsEnabled()) {
+      CppModuleMap moduleMap = ObjcRuleClasses.intermediateArtifacts(ruleContext).moduleMap();
+      ImmutableSet.Builder<Artifact> headers = ImmutableSet.builder();
+      for (J2ObjcSource j2ObjcSource : provider.getSrcs()) {
+        headers.addAll(j2ObjcSource.getObjcHdrs());
+      }
+      registerGenerateModuleMapAction(moduleMap, headers.build(), ImmutableList.<Artifact>of());
+    }
+    return this;
+  }
+
   private void registerJ2ObjcDeadCodeRemovalActions(Iterable<J2ObjcSource> j2ObjcSources,
       Iterable<String> entryClasses) {
     Artifact pruner = ruleContext.getPrerequisiteArtifact("$j2objc_dead_code_pruner", Mode.HOST);
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/IntermediateArtifacts.java b/src/main/java/com/google/devtools/build/lib/rules/objc/IntermediateArtifacts.java
index 59f9b07f67..923ed6c79f 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/IntermediateArtifacts.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/IntermediateArtifacts.java
@@ -17,8 +17,10 @@ package com.google.devtools.build.lib.rules.objc;
 import com.google.common.base.Optional;
 import com.google.common.base.Preconditions;
 import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.actions.Root;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
 import com.google.devtools.build.lib.analysis.RuleContext;
+import com.google.devtools.build.lib.rules.cpp.CppModuleMap;
 import com.google.devtools.build.lib.syntax.Label;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -28,7 +30,7 @@ import com.google.devtools.build.lib.vfs.PathFragment;
  */
 // TODO(bazel-team): This should really be named DerivedArtifacts as it contains methods for
 // final as well as intermediate artifacts.
-final class IntermediateArtifacts {
+public final class IntermediateArtifacts {
 
   /**
    * Extension used on the temporary zipped dsym bundle location. Must contain {@code .dSYM} for
@@ -100,6 +102,16 @@ final class IntermediateArtifacts {
   }
 
   /**
+   * Returns a derived artifact in the genfiles directory obtained by appending some extension to
+   * the end of the {@link PathFragment} corresponding to the owner {@link Label}.
+   */
+  private Artifact appendExtensionInGenfiles(String extension) {
+    PathFragment name = new PathFragment(ruleContext.getLabel().getName());
+    return scopedArtifact(
+        name.replaceName(name.getBaseName() + extension), /* inGenfiles = */ true);
+  }
+
+  /**
    * The output of using {@code actoolzip} to run {@code actool} for a given bundle which is
    * merged under the {@code .app} or {@code .bundle} directory root.
    */
@@ -161,23 +173,34 @@ final class IntermediateArtifacts {
     return appendExtension("_lipobin");
   }
 
-  private Artifact scopedArtifact(PathFragment scopeRelative) {
+  private Artifact scopedArtifact(PathFragment scopeRelative, boolean inGenfiles) {
+    Root root =
+        inGenfiles
+            ? ruleContext.getConfiguration().getGenfilesDirectory()
+            : ruleContext.getConfiguration().getBinDirectory();
     if (scopingLabel.isPresent()) {
       // The path of this artifact will be
       // RULE_PACKAGE/_intermediate_scoped/RULE_LABEL/SCOPING_PACKAGE/SCOPING_LABEL/SCOPERELATIVE
-      return ruleContext.getUniqueDirectoryArtifact("_intermediate_scoped",
-          scopingLabel.get().getPackageIdentifier().getPathFragment()
+      return ruleContext.getUniqueDirectoryArtifact(
+          "_intermediate_scoped",
+          scopingLabel
+              .get()
+              .getPackageIdentifier()
+              .getPathFragment()
               .getRelative(scopingLabel.get().getName())
               .getRelative(scopeRelative),
-          ruleContext.getConfiguration().getBinDirectory());
+          root);
     } else {
       // The path of this artifact will be
       // RULE_PACKAGE/SCOPERELATIVE
-      return ruleContext.getPackageRelativeArtifact(scopeRelative,
-          ruleContext.getConfiguration().getBinDirectory());
+      return ruleContext.getPackageRelativeArtifact(scopeRelative, root);
     }
   }
 
+  private Artifact scopedArtifact(PathFragment scopeRelative) {
+    return scopedArtifact(scopeRelative, /* inGenfiles = */ false);
+  }
+
   /**
    * The {@code .a} file which contains all the compiled sources for a rule.
    */
@@ -339,4 +362,23 @@ final class IntermediateArtifacts {
   public Artifact dotdFile(Artifact source) {
      return inUniqueObjsDir(source, ".d");
   }
+
+  /**
+   * {@link CppModuleMap} that provides the clang module map for this target.
+   */
+  public CppModuleMap moduleMap() {
+    if (!ObjcRuleClasses.objcConfiguration(ruleContext).moduleMapsEnabled()) {
+      throw new IllegalStateException();
+    }
+    String moduleName =
+        ruleContext
+            .getLabel()
+            .toString()
+            .replace("//", "")
+            .replace("/", "_")
+            .replace(":", "_");
+    // To get Swift to pick up module maps, we need to name them "module.modulemap" and have their
+    // parent directory in the module map search paths.
+    return new CppModuleMap(appendExtensionInGenfiles(".modulemaps/module.modulemap"), moduleName);
+  }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcLibrary.java b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcLibrary.java
index 0281538fbe..2e2b23eca0 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcLibrary.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcLibrary.java
@@ -27,6 +27,7 @@ import com.google.devtools.build.lib.analysis.RunfilesProvider;
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
 import com.google.devtools.build.lib.packages.Type;
 import com.google.devtools.build.lib.rules.RuleConfiguredTargetFactory;
+import com.google.devtools.build.lib.rules.cpp.CppModuleMap;
 import com.google.devtools.build.lib.rules.java.J2ObjcConfiguration;
 import com.google.devtools.build.lib.vfs.PathFragment;
 
@@ -97,6 +98,10 @@ public class J2ObjcLibrary implements RuleConfiguredTargetFactory {
           ImmutableList.of(j2objcSource.getObjcFilePath(), genDirHeaderSearchPath));
     }
 
+    if (ObjcRuleClasses.objcConfiguration(ruleContext).moduleMapsEnabled()) {
+      configureModuleMap(ruleContext, objcProviderBuilder, j2ObjcSrcsProvider);
+    }
+
     ObjcProvider objcProvider = objcProviderBuilder.build();
     xcodeSupport.addXcodeSettings(xcodeProviderBuilder, objcProvider, LIBRARY_STATIC);
 
@@ -111,6 +116,21 @@ public class J2ObjcLibrary implements RuleConfiguredTargetFactory {
         .build();
   }
 
+  /**
+   * Configures a module map for all the sources in {@code j2ObjcSrcsProvider}, registering
+   * an action to generate the module map and exposing that module map through {@code objcProvider}.
+   */
+  private void configureModuleMap(
+      RuleContext ruleContext,
+      ObjcProvider.Builder objcProvider,
+      J2ObjcSrcsProvider j2ObjcSrcsProvider) {
+    new CompilationSupport(ruleContext).registerJ2ObjcGenerateModuleMapAction(j2ObjcSrcsProvider);
+
+    CppModuleMap moduleMap = ObjcRuleClasses.intermediateArtifacts(ruleContext).moduleMap();
+    objcProvider.add(ObjcProvider.MODULE_MAP, moduleMap.getArtifact());
+    objcProvider.add(ObjcProvider.TOP_LEVEL_MODULE_MAP, moduleMap);
+  }
+
   private static void checkAttributes(RuleContext ruleContext) {
     checkAttributes(ruleContext, "deps");
     checkAttributes(ruleContext, "exports");
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java
index c4f70e36fe..08a69a6818 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java
@@ -152,12 +152,23 @@ public class ObjcCommandLineOptions extends FragmentOptions {
       help = "Uses these strings as objc fastbuild compiler options.")
   public List<String> fastbuildOptions;
 
-  @Option(name = "objc_enable_binary_stripping",
-      defaultValue = "false",
-      category = "flags",
-      help = "Whether to perform symbol and dead-code strippings on linked binaries. Binary "
-          + "strippings will be performed if both this flag and --compilationMode=opt are "
-          + "specified.")
+  @Option(
+    name = "experimental_objc_enable_module_maps",
+    defaultValue = "false",
+    category = "undocumented",
+    help = "Enables module map generation and interpretation."
+  )
+  public boolean enableModuleMaps;
+
+  @Option(
+    name = "objc_enable_binary_stripping",
+    defaultValue = "false",
+    category = "flags",
+    help =
+        "Whether to perform symbol and dead-code strippings on linked binaries. Binary "
+            + "strippings will be performed if both this flag and --compilationMode=opt are "
+            + "specified."
+  )
   public boolean enableBinaryStripping;
 
   // This option exists because two configurations are not allowed to have the same cache key
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommon.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommon.java
index 657062b730..775c53db8e 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommon.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommon.java
@@ -37,11 +37,13 @@ import static com.google.devtools.build.lib.rules.objc.ObjcProvider.INCLUDE_SYST
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.INSTRUMENTED_SOURCE;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.LIBRARY;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.LINKED_BINARY;
+import static com.google.devtools.build.lib.rules.objc.ObjcProvider.MODULE_MAP;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.SDK_DYLIB;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.SDK_FRAMEWORK;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.SOURCE;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.STORYBOARD;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.STRINGS;
+import static com.google.devtools.build.lib.rules.objc.ObjcProvider.TOP_LEVEL_MODULE_MAP;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.WEAK_SDK_FRAMEWORK;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.XCASSETS_DIR;
 import static com.google.devtools.build.lib.rules.objc.ObjcProvider.XCDATAMODEL;
@@ -63,10 +65,12 @@ import com.google.devtools.build.lib.packages.Type;
 import com.google.devtools.build.lib.rules.cpp.CcCommon;
 import com.google.devtools.build.lib.rules.cpp.CcLinkParamsProvider;
 import com.google.devtools.build.lib.rules.cpp.CppCompilationContext;
+import com.google.devtools.build.lib.rules.cpp.CppModuleMap;
 import com.google.devtools.build.lib.util.FileType;
 import com.google.devtools.build.lib.util.RegexFilter;
 import com.google.devtools.build.lib.vfs.PathFragment;
 
+import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
@@ -188,6 +192,46 @@ public final class ObjcCommon {
       }
       return optionsProvider.getCopts();
     }
+
+    /**
+     * The clang module maps of direct dependencies of this rule. These are needed to generate
+     * this rule's module map.
+     */
+    public List<CppModuleMap> moduleMapsForDirectDeps() {
+      // Make sure all dependencies that have headers are included here. If a module map is missing,
+      // its private headers will be treated as public!
+      ArrayList<CppModuleMap> moduleMaps = new ArrayList<>();
+      collectModuleMapsFromAttributeIfExists(moduleMaps, "deps");
+      collectModuleMapsFromAttributeIfExists(moduleMaps, "non_propagated_deps");
+      return moduleMaps;
+    }
+
+    /**
+     * Collects all module maps from the targets in a certain attribute and adds them into
+     * {@code moduleMaps}.
+     *
+     * @param moduleMaps an {@link ArrayList} to collect the module maps into
+     * @param attribute the name of a label list attribute to collect module maps from
+     */
+    private void collectModuleMapsFromAttributeIfExists(
+        ArrayList<CppModuleMap> moduleMaps, String attribute) {
+      if (ruleContext.attributes().has(attribute, Type.LABEL_LIST)) {
+        Iterable<ObjcProvider> providers =
+            ruleContext.getPrerequisites(attribute, Mode.TARGET, ObjcProvider.class);
+        for (ObjcProvider provider : providers) {
+          moduleMaps.addAll(provider.get(TOP_LEVEL_MODULE_MAP).toCollection());
+        }
+      }
+    }
+
+    /**
+     * Returns whether this target uses language features that require clang modules, such as
+     * @import.
+     */
+    public boolean enableModules() {
+      return ruleContext.attributes().has("enable_modules", Type.BOOLEAN)
+          && ruleContext.attributes().get("enable_modules", Type.BOOLEAN);
+    }
   }
 
   /**
@@ -248,6 +292,7 @@ public final class ObjcCommon {
     private Iterable<PathFragment> userHeaderSearchPaths = ImmutableList.of();
     private IntermediateArtifacts intermediateArtifacts;
     private boolean alwayslink;
+    private boolean hasModuleMap;
     private Iterable<Artifact> extraImportLibraries = ImmutableList.of();
     private Optional<Artifact> linkedBinary = Optional.absent();
     private Optional<Artifact> breakpadFile = Optional.absent();
@@ -341,6 +386,17 @@ public final class ObjcCommon {
     }
 
     /**
+     * Specifies that this target has a clang module map. This should be called if this target
+     * compiles sources or exposes headers for other targets to use. Note that this does not add
+     * the action to generate the module map. It simply indicates that it should be added to the
+     * provider.
+     */
+    Builder setHasModuleMap() {
+      this.hasModuleMap = true;
+      return this;
+    }
+
+    /**
      * Adds additional static libraries to be linked into the final ObjC application bundle.
      */
     Builder addExtraImportLibraries(Iterable<Artifact> extraImportLibraries) {
@@ -506,6 +562,12 @@ public final class ObjcCommon {
         }
       }
 
+      if (hasModuleMap && ObjcRuleClasses.objcConfiguration(context).moduleMapsEnabled()) {
+        CppModuleMap moduleMap = intermediateArtifacts.moduleMap();
+        objcProvider.add(MODULE_MAP, moduleMap.getArtifact());
+        objcProvider.add(TOP_LEVEL_MODULE_MAP, moduleMap);
+      }
+
       objcProvider.addAll(LINKED_BINARY, linkedBinary.asSet())
           .addAll(BREAKPAD_FILE, breakpadFile.asSet());
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java
index 8f073a18ad..9209c4ebda 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java
@@ -66,6 +66,7 @@ public class ObjcConfiguration extends BuildConfiguration.Fragment {
   private final boolean perProtoIncludes;
   private final List<String> fastbuildOptions;
   private final boolean enableBinaryStripping;
+  private final boolean moduleMapsEnabled;
   private final ConfigurationDistinguisher configurationDistinguisher;
   @Nullable private final Path clientWorkspaceRoot;
 
@@ -104,6 +105,7 @@ public class ObjcConfiguration extends BuildConfiguration.Fragment {
     this.perProtoIncludes = objcOptions.perProtoIncludes;
     this.fastbuildOptions = ImmutableList.copyOf(objcOptions.fastbuildOptions);
     this.enableBinaryStripping = objcOptions.enableBinaryStripping;
+    this.moduleMapsEnabled = objcOptions.enableModuleMaps;
     this.configurationDistinguisher = objcOptions.configurationDistinguisher;
     this.clientWorkspaceRoot = directories != null ? directories.getWorkspace() : null;
   }
@@ -261,6 +263,13 @@ public class ObjcConfiguration extends BuildConfiguration.Fragment {
   }
 
   /**
+   * Whether module map generation and interpretation is enabled.
+   */
+  public boolean moduleMapsEnabled() {
+    return moduleMapsEnabled;
+  }
+
+  /**
    * Returns the unique identifier distinguishing configurations that are otherwise the same.
    *
    * <p>Use this value for situations in which two configurations create two outputs that are the
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcImport.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcImport.java
index c3b35c22cc..143858de7d 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcImport.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcImport.java
@@ -16,6 +16,7 @@ package com.google.devtools.build.lib.rules.objc;
 
 import static com.google.devtools.build.lib.rules.objc.XcodeProductType.LIBRARY_STATIC;
 
+import com.google.common.base.Optional;
 import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
@@ -32,21 +33,24 @@ import com.google.devtools.build.lib.rules.objc.ObjcCommon.ResourceAttributes;
 public class ObjcImport implements RuleConfiguredTargetFactory {
   @Override
   public ConfiguredTarget create(RuleContext ruleContext) throws InterruptedException {
-    ObjcCommon common = new ObjcCommon.Builder(ruleContext)
-        .setCompilationAttributes(new CompilationAttributes(ruleContext))
-        .setResourceAttributes(new ResourceAttributes(ruleContext))
-        .setIntermediateArtifacts(ObjcRuleClasses.intermediateArtifacts(ruleContext))
-        .setAlwayslink(ruleContext.attributes().get("alwayslink", Type.BOOLEAN))
-        .addExtraImportLibraries(
-            ruleContext.getPrerequisiteArtifacts("archives", Mode.TARGET).list())
-        .addDepObjcProviders(
-            ruleContext.getPrerequisites("bundles", Mode.TARGET, ObjcProvider.class))
-        .build();
+    ObjcCommon common =
+        new ObjcCommon.Builder(ruleContext)
+            .setCompilationAttributes(new CompilationAttributes(ruleContext))
+            .setResourceAttributes(new ResourceAttributes(ruleContext))
+            .setIntermediateArtifacts(ObjcRuleClasses.intermediateArtifacts(ruleContext))
+            .setAlwayslink(ruleContext.attributes().get("alwayslink", Type.BOOLEAN))
+            .setHasModuleMap()
+            .addExtraImportLibraries(
+                ruleContext.getPrerequisiteArtifacts("archives", Mode.TARGET).list())
+            .addDepObjcProviders(
+                ruleContext.getPrerequisites("bundles", Mode.TARGET, ObjcProvider.class))
+            .build();
 
     XcodeProvider.Builder xcodeProviderBuilder = new XcodeProvider.Builder();
     NestedSetBuilder<Artifact> filesToBuild = NestedSetBuilder.stableOrder();
 
     new CompilationSupport(ruleContext)
+        .registerGenerateModuleMapAction(Optional.<CompilationArtifacts>absent())
         .addXcodeSettings(xcodeProviderBuilder, common)
         .validateAttributes();
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcLibrary.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcLibrary.java
index 98f4fe9597..e03d9ba814 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcLibrary.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcLibrary.java
@@ -68,14 +68,15 @@ public class ObjcLibrary implements RuleConfiguredTargetFactory {
         .addDepObjcProviders(ruleContext.getPrerequisites("deps", Mode.TARGET, ObjcProvider.class))
         .addDepObjcProviders(
             ruleContext.getPrerequisites("bundles", Mode.TARGET, ObjcProvider.class))
-        .addNonPropagatedDepObjcProviders(ruleContext.getPrerequisites("non_propagated_deps",
-            Mode.TARGET, ObjcProvider.class))
+        .addNonPropagatedDepObjcProviders(
+            ruleContext.getPrerequisites("non_propagated_deps", Mode.TARGET, ObjcProvider.class))
         .addDepCcHeaderProviders(
             ruleContext.getPrerequisites("deps", Mode.TARGET, CppCompilationContext.class))
         .addDepCcLinkProviders(
             ruleContext.getPrerequisites("deps", Mode.TARGET, CcLinkParamsProvider.class))
         .setIntermediateArtifacts(ObjcRuleClasses.intermediateArtifacts(ruleContext))
         .setAlwayslink(alwayslink)
+        .setHasModuleMap()
         .addExtraImportLibraries(extraImportLibraries)
         .addDepObjcProviders(extraDepObjcProviders)
         .build();
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProtoLibrary.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProtoLibrary.java
index 4057c25d50..8349b48d29 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProtoLibrary.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProtoLibrary.java
@@ -175,13 +175,16 @@ public class ObjcProtoLibrary implements RuleConfiguredTargetFactory {
     }
     ImmutableSet<PathFragment> searchPathEntries = searchPathEntriesBuilder.build();
 
-    ObjcCommon common = new ObjcCommon.Builder(ruleContext)
-        .setCompilationArtifacts(compilationArtifacts)
-        .addUserHeaderSearchPaths(searchPathEntries)
-        .addDepObjcProviders(ruleContext.getPrerequisites(
-            ObjcProtoLibraryRule.LIBPROTOBUF_ATTR, Mode.TARGET, ObjcProvider.class))
-        .setIntermediateArtifacts(intermediateArtifacts)
-        .build();
+    ObjcCommon common =
+        new ObjcCommon.Builder(ruleContext)
+            .setCompilationArtifacts(compilationArtifacts)
+            .addUserHeaderSearchPaths(searchPathEntries)
+            .addDepObjcProviders(
+                ruleContext.getPrerequisites(
+                    ObjcProtoLibraryRule.LIBPROTOBUF_ATTR, Mode.TARGET, ObjcProvider.class))
+            .setIntermediateArtifacts(intermediateArtifacts)
+            .setHasModuleMap()
+            .build();
 
     NestedSetBuilder<Artifact> filesToBuild = NestedSetBuilder.<Artifact>stableOrder()
         .addAll(common.getCompiledArchive().asSet())
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProvider.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProvider.java
index e8be3684fa..bbee7c675c 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProvider.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcProvider.java
@@ -27,6 +27,7 @@ import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
 import com.google.devtools.build.lib.collect.nestedset.Order;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.rules.cpp.CppModuleMap;
 import com.google.devtools.build.lib.rules.cpp.LinkerInputs;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.build.xcode.xcodegen.proto.XcodeGenProtos.TargetControl;
@@ -150,6 +151,19 @@ public final class ObjcProvider implements TransitiveInfoProvider {
   public static final Key<Flag> FLAG = new Key<>(STABLE_ORDER);
 
   /**
+   * Clang module maps, used to enforce proper use of private header files.
+   */
+  public static final Key<Artifact> MODULE_MAP = new Key<>(STABLE_ORDER);
+
+  /**
+   * Information about this provider's module map, in the form of a {@link CppModuleMap}. This
+   * is intransitive, and can be used to get just the target's module map to pass to clang or to
+   * get the module maps for direct but not transitive dependencies. You should only add module maps
+   * for this key using {@link Builder#addWithoutPropagating}.
+   */
+  public static final Key<CppModuleMap> TOP_LEVEL_MODULE_MAP = new Key<>(STABLE_ORDER);
+
+  /**
    * Merge zips to include in the bundle. The entries of these zip files are included in the final
    * bundle with the same path. The entries in the merge zips should not include the bundle root
    * path (e.g. {@code Foo.app}).
@@ -287,9 +301,10 @@ public final class ObjcProvider implements TransitiveInfoProvider {
     }
 
     @SuppressWarnings({"rawtypes", "unchecked"})
-    private void uncheckedAddAll(Key key, Iterable toAdd) {
-      maybeAddEmptyBuilder(items, key);
-      items.get(key).addAll(toAdd);
+    private void uncheckedAddAll(Key key, Iterable toAdd, boolean propagate) {
+      Map<Key<?>, NestedSetBuilder<?>> set = propagate ? items : nonPropagatedItems;
+      maybeAddEmptyBuilder(set, key);
+      set.get(key).addAll(toAdd);
     }
 
     @SuppressWarnings({"rawtypes", "unchecked"})
@@ -357,7 +372,7 @@ public final class ObjcProvider implements TransitiveInfoProvider {
      * Add element, and propagate it to any (transitive) dependers on this ObjcProvider.
      */
     public <E> Builder add(Key<E> key, E toAdd) {
-      uncheckedAddAll(key, ImmutableList.of(toAdd));
+      uncheckedAddAll(key, ImmutableList.of(toAdd), true);
       return this;
     }
 
@@ -365,7 +380,17 @@ public final class ObjcProvider implements TransitiveInfoProvider {
      * Add elements in toAdd, and propagate them to any (transitive) dependers on this ObjcProvider.
      */
     public <E> Builder addAll(Key<E> key, Iterable<? extends E> toAdd) {
-      uncheckedAddAll(key, toAdd);
+      uncheckedAddAll(key, toAdd, true);
+      return this;
+    }
+
+    /**
+     * Add element, but don't propagate dependers on this ObjcProvider. These elements will be
+     * exposed to {@link #get(Key)} calls, but not to any ObjcProviders which add this provider to
+     * themselves.
+     */
+    public <E> Builder addWithoutPropagating(Key<E> key, E toAdd) {
+      uncheckedAddAll(key, ImmutableList.of(toAdd), false);
       return this;
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java
index 04be1426cd..7b53bcae59 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java
@@ -74,8 +74,8 @@ public class ObjcRuleClasses {
     throw new UnsupportedOperationException("static-only");
   }
 
-  static IntermediateArtifacts intermediateArtifacts(RuleContext ruleContext) {
-    return new IntermediateArtifacts(ruleContext, /*archiveFileNameSuffix=*/"");
+  public static IntermediateArtifacts intermediateArtifacts(RuleContext ruleContext) {
+    return new IntermediateArtifacts(ruleContext, /*archiveFileNameSuffix=*/ "");
   }
 
   /**
@@ -617,68 +617,75 @@ public class ObjcRuleClasses {
     public RuleClass build(Builder builder, RuleDefinitionEnvironment env) {
       return builder
           /* <!-- #BLAZE_RULE($objc_compiling_rule).ATTRIBUTE(srcs) -->
-          The list of C, C++, Objective-C, and Objective-C++ source and header
-          files that are processed to create the library target.
-          ${SYNOPSIS}
-          These are your checked-in files, plus any generated files.
-          Source files are compiled into .o files with Clang. Header files
-          may be included/imported by any source or header in the srcs attribute
-          of this target, but not by headers in hdrs or any targets that depend
-          on this rule.
-          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
-          .add(attr("srcs", LABEL_LIST)
-              .direct_compile_time_input()
-              .allowedFileTypes(SRCS_TYPE))
+           The list of C, C++, Objective-C, and Objective-C++ source and header
+           files that are processed to create the library target.
+           ${SYNOPSIS}
+           These are your checked-in files, plus any generated files.
+           Source files are compiled into .o files with Clang. Header files
+           may be included/imported by any source or header in the srcs attribute
+           of this target, but not by headers in hdrs or any targets that depend
+           on this rule.
+           <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+          .add(attr("srcs", LABEL_LIST).direct_compile_time_input().allowedFileTypes(SRCS_TYPE))
           /* <!-- #BLAZE_RULE($objc_compiling_rule).ATTRIBUTE(non_arc_srcs) -->
-          The list of Objective-C files that are processed to create the
-          library target that DO NOT use ARC.
-          ${SYNOPSIS}
-          The files in this attribute are treated very similar to those in the
-          srcs attribute, but are compiled without ARC enabled.
-          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
-          .add(attr("non_arc_srcs", LABEL_LIST)
-              .direct_compile_time_input()
-              .allowedFileTypes(NON_ARC_SRCS_TYPE))
+           The list of Objective-C files that are processed to create the
+           library target that DO NOT use ARC.
+           ${SYNOPSIS}
+           The files in this attribute are treated very similar to those in the
+           srcs attribute, but are compiled without ARC enabled.
+           <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+          .add(
+              attr("non_arc_srcs", LABEL_LIST)
+                  .direct_compile_time_input()
+                  .allowedFileTypes(NON_ARC_SRCS_TYPE))
           /* <!-- #BLAZE_RULE($objc_compiling_rule).ATTRIBUTE(pch) -->
-          Header file to prepend to every source file being compiled (both arc
-          and non-arc).
-          ${SYNOPSIS}
-          Note that the file will not be precompiled - this is simply a
-          convenience, not a build-speed enhancement.
-          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
-          .add(attr("pch", LABEL)
-              .direct_compile_time_input()
-              .allowedFileTypes(FileType.of(".pch")))
+           Header file to prepend to every source file being compiled (both arc
+           and non-arc).
+           ${SYNOPSIS}
+           Note that the file will not be precompiled - this is simply a
+           convenience, not a build-speed enhancement.
+           <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+          .add(attr("pch", LABEL).direct_compile_time_input().allowedFileTypes(FileType.of(".pch")))
           /* <!-- #BLAZE_RULE($objc_compiling_rule).ATTRIBUTE(deps) -->
-          The list of targets that are linked together to form the final bundle.
-          ${SYNOPSIS}
-          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
-          .override(attr("deps", LABEL_LIST)
-              .direct_compile_time_input()
-              .allowedRuleClasses(ALLOWED_DEPS_RULE_CLASSES)
-              .allowedFileTypes())
+           The list of targets that are linked together to form the final bundle.
+           ${SYNOPSIS}
+           <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+          .override(
+              attr("deps", LABEL_LIST)
+                  .direct_compile_time_input()
+                  .allowedRuleClasses(ALLOWED_DEPS_RULE_CLASSES)
+                  .allowedFileTypes())
           /* <!-- #BLAZE_RULE($objc_compiling_rule).ATTRIBUTE(non_propagated_deps) -->
-          The list of targets that are required in order to build this target,
-          but which are not included in the final bundle.
-          ${SYNOPSIS}
-          This attribute should only rarely be used, and probably only for proto
-          dependencies.
-          ${SYNOPSIS}
-          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
-          .add(attr("non_propagated_deps", LABEL_LIST)
-              .direct_compile_time_input()
-              .allowedRuleClasses(ALLOWED_DEPS_RULE_CLASSES)
-              .allowedFileTypes())
+           The list of targets that are required in order to build this target,
+           but which are not included in the final bundle.
+           ${SYNOPSIS}
+           This attribute should only rarely be used, and probably only for proto
+           dependencies.
+           ${SYNOPSIS}
+           <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+          .add(
+              attr("non_propagated_deps", LABEL_LIST)
+                  .direct_compile_time_input()
+                  .allowedRuleClasses(ALLOWED_DEPS_RULE_CLASSES)
+                  .allowedFileTypes())
           /* <!-- #BLAZE_RULE($objc_compiling_rule).ATTRIBUTE(defines) -->
-          Extra <code>-D</code> flags to pass to the compiler. They should be in
-          the form <code>KEY=VALUE</code> or simply <code>KEY</code> and are
-          passed not only the compiler for this target (as <code>copts</code>
-          are) but also to all <code>objc_</code> dependers of this target.
-          ${SYNOPSIS}
-          Subject to <a href="#make_variables">"Make variable"</a> substitution and
-          <a href="#sh-tokenization">Bourne shell tokenization</a>.
-          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+           Extra <code>-D</code> flags to pass to the compiler. They should be in
+           the form <code>KEY=VALUE</code> or simply <code>KEY</code> and are
+           passed not only the compiler for this target (as <code>copts</code>
+           are) but also to all <code>objc_</code> dependers of this target.
+           ${SYNOPSIS}
+           Subject to <a href="#make_variables">"Make variable"</a> substitution and
+           <a href="#sh-tokenization">Bourne shell tokenization</a>.
+           <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
           .add(attr("defines", STRING_LIST))
+          /* <!-- #BLAZE_RULE($objc_compiling_rule).ATTRIBUTE(enable_modules) -->
+           Enables clang module support (via -fmodules).
+           ${SYNOPSIS}
+           Setting this to 1 will allow you to @import system headers and other targets:
+           @import UIKit;
+           @import path_to_package_target;
+           <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+          .add(attr("enable_modules", BOOLEAN))
           .build();
     }
     @Override