Propagate '-application-extension' to module interface loader sub-invocations.

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1559,6 +1559,11 @@ InterfaceSubContextDelegateImpl::InterfaceSubContextDelegateImpl(
     genericSubInvocation.getFrontendOptions().DisableImplicitModules = true;
     GenericArgs.push_back("-disable-implicit-swift-modules");
   }
+  // If building an application extension, make sure API use
+  // is restricted accordingly in downstream dependnecies.
+  if (langOpts.EnableAppExtensionRestrictions) {
+    GenericArgs.push_back("-application-extension");
+  }
   // Save the parent invocation's Target Triple
   ParentInvocationTarget = langOpts.Target;
 

test/ModuleInterface/Inputs/extension-available.swift

@@ -0,0 +1,3 @@
+@available(macOS 10.0, *)
+public func extensionAvailable() {
+}

test/ModuleInterface/extension-transitive-availability.swift

@@ -0,0 +1,48 @@
+// This test ensures that the parent invocation's '-application-extension' flag is inherited when building dependency modules
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-emit-module-interface(%t/ExtensionAvailable.swiftinterface) %S/Inputs/extension-available.swift -module-name ExtensionAvailable -I%t -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
+
+// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I%t -application-extension -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
+// RUN: %FileCheck %s < %t/deps.json
+
+import ExtensionAvailable
+func foo() {
+    extensionAvailable()
+}
+
+// CHECK:      "directDependencies": [
+// CHECK-NEXT:        {
+// CHECK-NEXT:          "swift": "ExtensionAvailable"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        {
+// CHECK-NEXT:          "swift": "Swift"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        {
+// CHECK-NEXT:          "swift": "SwiftOnoneSupport"
+// CHECK-NEXT:        }
+// CHECK-NEXT:      ],
+
+
+// CHECK:      "swift": "ExtensionAvailable"
+// CHECK-NEXT:    },
+// CHECK-NEXT:    {
+// CHECK-NEXT:      "modulePath": "ExtensionAvailable.swiftmodule",
+// CHECK-NEXT:      "sourceFiles": [
+// CHECK-NEXT:      ],
+// CHECK-NEXT:      "directDependencies": [
+// CHECK-NEXT:        {
+// CHECK-NEXT:          "swift": "Swift"
+// CHECK-NEXT:        },
+// CHECK-NEXT:        {
+// CHECK-NEXT:          "swift": "SwiftOnoneSupport"
+// CHECK-NEXT:        }
+// CHECK-NEXT:      ],
+// CHECK-NEXT:      "details": {
+// CHECK-NEXT:        "swift": {
+// CHECK-NEXT:          "moduleInterfacePath": 
+// CHECK-NEXT:          "contextHash":
+// CHECK-NEXT:          "commandLine": [
+// CHECK-NEXT:            "-frontend",
+// CHECK-NEXT:            "-compile-module-from-interface",
+// CHECK:            "-application-extension",