Sema: Loosen exportability checking for non-publicly imported types

This one is specific. Allow extensions to define public members to
package types implicitly exporting their memory layout when imported
non-publicly.

Enabling exportability checks for non-library-evolution by default as a
warning triggered marking such types as implicitly exported to clients.
This in turn enabled erroring on the extensions in clients when imported
non-publicly. This error would be source breaking and shouldn't be
required in such a context. We may even consider lifting this
restriction entierly, even for public types imported non-public.

Author: xymus

lib/AST/Availability.cpp

@@ -1062,5 +1062,5 @@ ExportedLevel swift::isExported(const ExtensionDecl *ED) {
   for (const Decl *D : ED->getMembers())
     membersExported = std::max(membersExported, isExported(D));
 
-  return membersExported;
+  return std::min(exported, membersExported);
 }

lib/Sema/ResilienceDiagnostics.cpp

@@ -252,7 +252,12 @@ static bool shouldDiagnoseDeclAccess(const ValueDecl *D,
   switch (*reason) {
   case ExportabilityReason::ExtensionWithPublicMembers:
   case ExportabilityReason::ExtensionWithConditionalConformances:
-    return true;
+    // Allow public members in extensions of implicitly exported types.
+    // Extensions cannot define stored variables avoiding the memory layout
+    // concerns and we don't print swiftinterfaces in non-library-evolution
+    // mode.
+    // We may want to allow to simply return false and always allow this.
+    return where.getExportedLevel() == ExportedLevel::Exported;
   case ExportabilityReason::Inheritance:
   case ExportabilityReason::ImplicitlyPublicInheritance:
     return isa<ProtocolDecl>(D);

test/Sema/access-level-import-classic-exportability.swift

@@ -1,30 +1,52 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file --leading-lines %s %t
 
-/// Build the libraries.
+/// Non-library-evolution.
+// RUN: %target-swift-frontend -emit-module %t/PublicLib.swift -o %t
+// RUN: %target-swift-frontend -emit-module %t/PackageLib.swift -o %t
+// RUN: %target-swift-frontend -emit-module %t/InternalLib.swift -o %t \
+// RUN:   -package-name pkg
+// RUN: %target-swift-frontend -emit-module %t/FileprivateLib.swift -o %t
+// RUN: %target-swift-frontend -emit-module %t/PrivateLib.swift -o %t
+
+/// Check diagnostics.
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   -package-name pkg -swift-version 5 \
+// RUN:   -verify -verify-ignore-unrelated
+
+/// CheckImplementationOnly doesn't change the results.
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   -package-name pkg -swift-version 5 \
+// RUN:   -enable-experimental-feature CheckImplementationOnly \
+// RUN:   -verify -verify-ignore-unrelated
+
+
+/// Library-evolution.
 // RUN: %target-swift-frontend -emit-module %t/PublicLib.swift -o %t \
 // RUN:   -enable-library-evolution
 // RUN: %target-swift-frontend -emit-module %t/PackageLib.swift -o %t \
 // RUN:   -enable-library-evolution
 // RUN: %target-swift-frontend -emit-module %t/InternalLib.swift -o %t \
-// RUN:   -enable-library-evolution
+// RUN:   -enable-library-evolution -package-name pkg
 // RUN: %target-swift-frontend -emit-module %t/FileprivateLib.swift -o %t \
 // RUN:   -enable-library-evolution
 // RUN: %target-swift-frontend -emit-module %t/PrivateLib.swift -o %t \
 // RUN:   -enable-library-evolution
 
 /// Check diagnostics.
 // RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
-// RUN:   -package-name TestPackage -swift-version 5 \
-// RUN:   -enable-experimental-feature AccessLevelOnImport -verify -verify-ignore-unrelated
+// RUN:   -package-name pkg -swift-version 5 \
+// RUN:   -enable-library-evolution \
+// RUN:   -verify -verify-ignore-unrelated
 
-/// Check diagnostics with library-evolution.
+/// CheckImplementationOnly doesn't change the results.
 // RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
-// RUN:   -package-name TestPackage -swift-version 5 \
+// RUN:   -package-name pkg -swift-version 5 \
 // RUN:   -enable-library-evolution \
-// RUN:   -enable-experimental-feature AccessLevelOnImport -verify -verify-ignore-unrelated
+// RUN:   -enable-experimental-feature CheckImplementationOnly \
+// RUN:   -verify -verify-ignore-unrelated
 
-// REQUIRES: swift_feature_AccessLevelOnImport
+// REQUIRES: swift_feature_CheckImplementationOnly
 
 //--- PublicLib.swift
 public struct PublicImportType {
@@ -41,6 +63,8 @@ public struct InternalImportType {
     public init() {}
 }
 
+package struct InternalImportPackageType {}
+
 //--- FileprivateLib.swift
 public struct FileprivateImportType {
     public init() {}
@@ -141,6 +165,9 @@ extension Array: InternalConstrainedExtensionProtoInFileprivate where Element ==
 extension InternalImportType {
     fileprivate func fileprivateMethod() {}
 }
+extension InternalImportPackageType { // No error
+    public func foo() {}
+}
 
 private protocol InternalConstrainedExtensionProtoInPrivate {}
 extension Array: InternalConstrainedExtensionProtoInPrivate where Element == InternalImportType {}