Sema: Intro the CheckImplementationOnlyStrict feature

Author: xymus

include/swift/Basic/Features.def

@@ -557,6 +557,10 @@ EXPERIMENTAL_FEATURE(AnyAppleOSAvailability, true)
 /// Check @_implementationOnly imports in non-library-evolution mode.
 EXPERIMENTAL_FEATURE(CheckImplementationOnly, true)
 
+/// Extends CheckImplementationOnly with an extra check at serialization to
+/// report references to implementation-only imported modules.
+EXPERIMENTAL_FEATURE(CheckImplementationOnlyStrict, false)
+
 #undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE

lib/AST/FeatureSet.cpp

@@ -145,6 +145,7 @@ UNINTERESTING_FEATURE(GroupActorErrors)
 UNINTERESTING_FEATURE(SameElementRequirements)
 UNINTERESTING_FEATURE(SendingArgsAndResults)
 UNINTERESTING_FEATURE(CheckImplementationOnly)
+UNINTERESTING_FEATURE(CheckImplementationOnlyStrict)
 
 static bool findUnderscoredLifetimeAttr(Decl *decl) {
   auto hasUnderscoredLifetimeAttr = [](Decl *decl) {

lib/Frontend/CompilerInvocation.cpp

@@ -1897,6 +1897,10 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.enableFeature(Feature::NoExplicitNonIsolated);
   }
 
+  if (Opts.hasFeature(Feature::CheckImplementationOnlyStrict) &&
+      !::getenv("SWIFT_DISABLE_IMPLICIT_CHECK_IMPLEMENTATION_ONLY"))
+    Opts.enableFeature(Feature::CheckImplementationOnly);
+
 #if !defined(NDEBUG) && SWIFT_ENABLE_EXPERIMENTAL_PARSER_VALIDATION
   /// Enable round trip parsing via the new swift parser unless it is disabled
   /// explicitly. The new Swift parser can have mismatches with C++ parser -

lib/Sema/TypeCheckAttr.cpp

@@ -5051,7 +5051,8 @@ AttributeChecker::visitImplementationOnlyAttr(ImplementationOnlyAttr *attr) {
 
   // @_implementationOnly on types only applies to non-public types.
   if (isa<NominalTypeDecl>(D)) {
-    if (!Ctx.LangOpts.hasFeature(Feature::CheckImplementationOnly)) {
+    if (!Ctx.LangOpts.hasFeature(Feature::CheckImplementationOnly) &&
+        !Ctx.LangOpts.hasFeature(Feature::CheckImplementationOnlyStrict)) {
       diagnoseAndRemoveAttr(attr, diag::implementation_only_on_types_feature);
       return;
     }

test/Sema/hidden-memory-layout.swift

@@ -48,8 +48,17 @@
 // RUN:   -verify-additional-prefix embedded-opt-in- \
 // RUN:   -enable-experimental-feature CheckImplementationOnly
 
+/// Same diags with CheckImplementationOnlyStrict
+// RUN: %target-swift-frontend -typecheck -verify -verify-ignore-unrelated %s -I %t \
+// RUN:   -swift-version 5 -target arm64-apple-none-macho \
+// RUN:   -enable-experimental-feature Embedded \
+// RUN:   -verify-additional-prefix opt-in- -DUseImplementationOnly \
+// RUN:   -verify-additional-prefix embedded-opt-in- \
+// RUN:   -enable-experimental-feature CheckImplementationOnlyStrict
+
 // REQUIRES: swift_feature_Embedded
 // REQUIRES: swift_feature_CheckImplementationOnly
+// REQUIRES: swift_feature_CheckImplementationOnlyStrict
 // REQUIRES: embedded_stdlib_cross_compiling
 
 @_implementationOnly import directs