Add Bridging Header attribute to objc_ compilation rules

This allows Swift code to import and use Objective-C interfaces.

--
MOS_MIGRATED_REVID=100715248

3 files changed, 22 insertions, 4 deletions

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 5af6e94f81..a934f09b26 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
@@ -291,9 +291,15 @@ final class CompilationSupport {
       .addExecPath("-o", objFile)
       .addExecPath("-emit-module-path", intermediateArtifacts.swiftModuleFile(sourceFile));
 
-    // Add all ObjC headers to the compiler, in case Swift code is calling into Objc
-    // TODO(bazel-team): This can be augmented by an explicit bridging header field in the rule.
-    commandLine.addBeforeEachExecPath("-import-objc-header", attributes.hdrs());
+
+    ImmutableList.Builder<Artifact> inputHeaders = ImmutableList.builder();
+    inputHeaders.addAll(attributes.hdrs());
+
+    Optional<Artifact> bridgingHeader = attributes.bridgingHeader();
+    if (bridgingHeader.isPresent()) {
+      commandLine.addExecPath("-import-objc-header", bridgingHeader.get());
+      inputHeaders.add(bridgingHeader.get());
+    }
 
     ruleContext.registerAction(ObjcRuleClasses.spawnOnDarwinActionBuilder()
         .setMnemonic("SwiftCompile")
@@ -301,7 +307,7 @@ final class CompilationSupport {
         .setCommandLine(commandLine.build())
         .addInput(sourceFile)
         .addInputs(otherSwiftSources)
-        .addInputs(attributes.hdrs())
+        .addInputs(inputHeaders.build())
         .addOutput(objFile)
         .addOutput(intermediateArtifacts.swiftModuleFile(sourceFile))
         .build(ruleContext));
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 688fa13738..030164eaf4 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
@@ -96,6 +96,11 @@ public final class ObjcCommon {
       return ImmutableList.copyOf(CcCommon.getHeaders(ruleContext));
     }
 
+    Optional<Artifact> bridgingHeader() {
+      Artifact header = ruleContext.getPrerequisiteArtifact("bridging_header", Mode.TARGET);
+      return Optional.fromNullable(header);
+    }
+
     Iterable<PathFragment> includes() {
       return Iterables.transform(
           ruleContext.attributes().get("includes", Type.STRING_LIST),
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 52b6a38896..e7129e5215 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
@@ -519,6 +519,13 @@ public class ObjcRuleClasses {
           .add(attr("hdrs", LABEL_LIST)
               .direct_compile_time_input()
               .allowedFileTypes(HDRS_TYPE))
+          /* <!-- #BLAZE_RULE($objc_compile_dependency_rule).ATTRIBUTE(bridging_header) -->
+          A header defining the Objective-C interfaces to be exposed in Swift.
+          ${SYNOPSIS}
+          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
+          .add(attr("bridging_header", Type.LABEL)
+              .direct_compile_time_input()
+              .allowedFileTypes(HDRS_TYPE))
           /* <!-- #BLAZE_RULE($objc_compile_dependency_rule).ATTRIBUTE(includes) -->
           List of <code>#include/#import</code> search paths to add to this target
           and all depending targets.