Merge pull request #60075 from tshortli/weak-link-associated-conformance-descriptor-5.7

[5.7] IRGen: Weakly link associated conformance descriptors when either the protocol or the associated requirement is weak

Author: tshortli

lib/IRGen/Linking.cpp

@@ -1158,9 +1158,12 @@ bool LinkEntity::isWeakImported(ModuleDecl *module) const {
 
   case Kind::AssociatedConformanceDescriptor:
   case Kind::DefaultAssociatedConformanceAccessor: {
-    // Associated conformance descriptors use the protocol as
-    // their declaration, but are weak linked if the associated
-    // type stored in extra storage area is weak linked.
+    // Associated conformance descriptors use the protocol as their declaration
+    // and are weak linked if either the protocol or the associated type stored
+    // in extra storage area is weak linked.
+    if (cast<ProtocolDecl>(getDecl())->isWeakImported(module))
+      return true;
+
     auto assocConformance = getAssociatedConformance();
     auto *depMemTy = assocConformance.first->castTo<DependentMemberType>();
     return depMemTy->getAssocType()->isWeakImported(module);

test/IRGen/weak_import_associated_conformance_descriptor.swift

@@ -0,0 +1,58 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/Library.swiftmodule -parse-as-library %t/Library.swift -enable-library-evolution
+// RUN: %target-swift-frontend -primary-file %t/Client.swift -I %t -emit-ir | %FileCheck %s
+
+// REQUIRES: OS=macosx
+
+//--- Library.swift
+
+public protocol P { }
+public protocol Q: P { }
+
+public protocol StrongProtoWithAssoc {
+  associatedtype Assoc: P
+}
+
+public protocol StrongProtoWithWeakLinkedAssoc {
+  @_weakLinked associatedtype Assoc: P
+}
+
+@available(macOS 10.50, *)
+public protocol WeakProtoWithAssoc {
+  associatedtype Assoc: P
+}
+
+@available(macOS 10.50, *)
+public protocol WeakProtoWithStrongInheritedAssoc: StrongProtoWithAssoc where Self.Assoc: Q { }
+
+
+//--- Client.swift
+
+import Library
+
+struct ConformsToP: P { }
+struct ConformsToQ: Q { }
+
+// CHECK: @"$s7Library20StrongProtoWithAssocP0E0AC_AA1PTn" = external global %swift.protocol_requirement, align 4
+struct ConformsToStrongProtoWithAssoc: StrongProtoWithAssoc {
+  typealias Assoc = ConformsToP
+}
+
+// CHECK: @"$s7Library30StrongProtoWithWeakLinkedAssocP0G0AC_AA1PTn" = extern_weak global %swift.protocol_requirement, align 4
+struct ConformsToStrongProtoWithWeakLinkedAssoc: StrongProtoWithWeakLinkedAssoc {
+  typealias Assoc = ConformsToP
+}
+
+// CHECK: @"$s7Library18WeakProtoWithAssocP0E0AC_AA1PTn" = extern_weak global %swift.protocol_requirement, align 4
+@available(macOS 10.50, *)
+struct ConformsToWeakProtoWithAssoc: WeakProtoWithAssoc {
+  typealias Assoc = ConformsToP
+}
+
+// CHECK: @"$s7Library33WeakProtoWithStrongInheritedAssocP0G0AA0ecdG0P_AA1QTn" = extern_weak global %swift.protocol_requirement, align 4
+@available(macOS 10.50, *)
+struct ConformsToWeakProtoWithStrongInheritedAssoc: WeakProtoWithStrongInheritedAssoc {
+  typealias Assoc = ConformsToQ
+}