NFC: Add tests verifying that @_weakLinked import is not transitive.

Author: tshortli

test/IRGen/weaklinked_import_transitive.swift

@@ -0,0 +1,19 @@
+// RUN: %empty-directory(%t)
+//
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/weaklinked_import_helper.swiftmodule -parse-as-library %S/Inputs/weaklinked_import_helper.swift -enable-library-evolution
+//
+// RUN: echo '@_weakLinked import weaklinked_import_helper' > %t/intermediate.swift
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/intermediate.swiftmodule -parse-as-library %t/intermediate.swift -I %t -enable-library-evolution
+//
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir | %FileCheck %s
+
+// UNSUPPORTED: OS=windows-msvc
+
+import intermediate
+import weaklinked_import_helper
+
+// Symbols from weaklinked_import_helper should be strong, despite intermediate
+// importining the module @_weakLinked.
+
+// CHECK-DAG: declare swiftcc {{.+}} @"$s24weaklinked_import_helper2fnyyF"()
+fn()

test/ModuleInterface/weaklinked-import.swift

@@ -0,0 +1,14 @@
+// RUN: %empty-directory(%t)
+//
+// RUN: echo 'public struct S {}' > %t/Other.swift
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/Other.swiftmodule -parse-as-library %t/Other.swift -enable-library-evolution
+//
+// RUN: %target-swift-emit-module-interface(%t/WeakLinksOther.swiftinterface) %s -I %t
+// RUN: %target-swift-typecheck-module-from-interface(%t/WeakLinksOther.swiftinterface) -I %t
+// RUN: %FileCheck %s < %t/WeakLinksOther.swiftinterface
+
+// UNSUPPORTED: OS=windows-msvc
+
+// The @_weakLinked attribute should not be printed in swiftinterfaces.
+// CHECK-NOT: @_weakLinked
+@_weakLinked import Other