SIL: Stored property initializers in non-resilient modules might need public linkage

Because of a ill-advised core team decision, Swift now
allows @_inlineable root initializers on types that
are not @_fixed_layout (aa85e45).

Since stored property initializers of types that are not
@_fixed_layout are permitted to reference non-public symbols,
they cannot be serialized and must instead have public
linkage. This negates most of the benefit of inlining the
constructor in the first place, but oh well.

This does not affect resilient builds.

Fixes <rdar://problem/38439363>.

Author: slavapestov

lib/SIL/SILDeclRef.cpp

@@ -285,19 +285,29 @@ SILLinkage SILDeclRef::getLinkage(ForDefinition_t forDefinition) const {
 
   // Stored property initializers get the linkage of their containing type.
   if (isStoredPropertyInitializer()) {
-    // If the type is public, the property initializer is referenced from
-    // inlinable initializers, and has PublicNonABI linkage.
+    // Three cases:
     //
-    // Note that we don't serialize the presence of an initializer, so there's
-    // no way to reference one from another module except for this case.
+    // 1) Type is formally @_fixed_layout. Root initializers can be declared
+    //    @_inlineable. The property initializer must only reference
+    //    public symbols, and is serialized, so we give it PublicNonABI linkage.
+    //
+    // 2) Type is not formally @_fixed_layout and the module is not resilient.
+    //    Root initializers can be declared @_inlineable. This is the annoying
+    //    case. We give the initializer public linkage if the type is public.
+    //
+    // 3) Type is resilient. The property initializer is never public because
+    //    root initializers cannot be @_inlineable.
+    //
+    // FIXME: Get rid of case 2 somehow.
     if (isSerialized())
       return maybeAddExternal(SILLinkage::PublicNonABI);
 
-    // Otherwise, use the visibility of the type itself, because even if the
-    // property is private, we might reference the initializer from another
-    // file.
     d = cast<NominalTypeDecl>(d->getDeclContext());
-    neverPublic = true;
+
+    // FIXME: This should always be true.
+    if (d->getDeclContext()->getParentModule()->getResilienceStrategy() ==
+        ResilienceStrategy::Resilient)
+      neverPublic = true;
   }
 
   // The global addressor is never public for resilient globals.

test/SILGen/extensions_multifile.swift

@@ -1,4 +1,5 @@
-// RUN: %target-swift-frontend -emit-silgen -primary-file %s %S/Inputs/struct_with_initializer.swift -module-name extensions_multifile -enable-sil-ownership | %FileCheck %s
+// RUN: %target-swift-frontend -emit-silgen -primary-file %s %S/Inputs/struct_with_initializer.swift -module-name extensions_multifile -enable-sil-ownership | %FileCheck %s --check-prefix=FRAGILE --check-prefix=CHECK
+// RUN: %target-swift-frontend -emit-silgen -primary-file %s %S/Inputs/struct_with_initializer.swift -module-name extensions_multifile -enable-sil-ownership -enable-resilience | %FileCheck %s --check-prefix=RESILIENT --check-prefix=CHECK
 
 // CHECK-LABEL: sil hidden @$S20extensions_multifile12HasInitValueV1zACSi_tcfC : $@convention(method) (Int, @thin HasInitValue.Type) -> @owned HasInitValue {
 // CHECK: function_ref @$S20extensions_multifile12HasInitValueV1xSivpfi : $@convention(thin) () -> Int
@@ -15,7 +16,9 @@ extension HasPrivateInitValue {
   init(z: Int) {}
 }
 
-// CHECK-LABEL: sil hidden_external [transparent] @$S20extensions_multifile24PublicStructHasInitValueV1xSivpfi : $@convention(thin) () -> Int
+// FRAGILE-LABEL: sil [transparent] @$S20extensions_multifile24PublicStructHasInitValueV1xSivpfi : $@convention(thin) () -> Int
+
+// RESILIENT-LABEL: sil hidden_external [transparent] @$S20extensions_multifile24PublicStructHasInitValueV1xSivpfi : $@convention(thin) () -> Int
 
 extension PublicStructHasInitValue {
   init(z: Int) {}

test/SILGen/fixed_layout_attribute.swift

@@ -20,7 +20,8 @@ public struct NonFixedStruct {
   public var storedProperty = global
 }
 
-// CHECK-LABEL: sil hidden [transparent] @$S22fixed_layout_attribute14NonFixedStructV14storedPropertySivpfi : $@convention(thin) () -> Int
+// FRAGILE-LABEL: sil [transparent] @$S22fixed_layout_attribute14NonFixedStructV14storedPropertySivpfi : $@convention(thin) () -> Int
+// RESILIENT-LABEL: sil hidden [transparent] @$S22fixed_layout_attribute14NonFixedStructV14storedPropertySivpfi : $@convention(thin) () -> Int
 //
 //    ... okay to directly reference the addressor here:
 // CHECK: function_ref @$S22fixed_layout_attribute6globalSivau