[Sema] Intro flag to default imports to internal, the Swift 6 mode

The feature InternalImportsByDefault makes imports default to internal instead
of public. Applying the Swift 6 behavior of SE-0409 in Swift 5.

Let's use only that flag to track the Swift 6 behavior as well instead
of separately checking for the language version.

Author: xymus

include/swift/Basic/Features.def

@@ -117,6 +117,7 @@ UPCOMING_FEATURE(BareSlashRegexLiterals, 354, 6)
 UPCOMING_FEATURE(ExistentialAny, 335, 6)
 UPCOMING_FEATURE(ImportObjcForwardDeclarations, 384, 6)
 UPCOMING_FEATURE(DisableOutwardActorInference, 401, 6)
+UPCOMING_FEATURE(InternalImportsByDefault, 409, 6)
 
 EXPERIMENTAL_FEATURE(StaticAssert, false)
 EXPERIMENTAL_FEATURE(NamedOpaqueTypes, false)

lib/AST/ASTPrinter.cpp

@@ -3436,6 +3436,10 @@ static bool usesFeatureDisableOutwardActorInference(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureInternalImportsByDefault(Decl *decl) {
+  return false;
+}
+
 static bool usesFeatureImportSymbolicCXXDecls(Decl *decl) { return false; }
 
 static bool usesFeatureGenerateBindingsForThrowingFunctionsInCXX(Decl *decl) {

lib/AST/Decl.cpp

@@ -1506,9 +1506,8 @@ AccessLevel ImportDecl::getAccessLevel() const {
   }
 
   auto &LangOpts = getASTContext().LangOpts;
-  if (LangOpts.isSwiftVersionAtLeast(6) &&
-      LangOpts.hasFeature(Feature::AccessLevelOnImport)) {
-    // Tentative Swift 6 mode where the default import is internal.
+  if (LangOpts.hasFeature(Feature::InternalImportsByDefault)) {
+    // Swift 6 mode where the default import is internal.
     return AccessLevel::Internal;
   } else {
     return AccessLevel::Public;

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -233,6 +233,7 @@ static void printImports(raw_ostream &out,
                          ModuleDecl *M,
                          const llvm::SmallSet<StringRef, 4>
                            &AliasModuleNamesTargets) {
+  auto &ctx = M->getASTContext();
   // FIXME: This is very similar to what's in Serializer::writeInputBlock, but
   // it's not obvious what higher-level optimization would be factored out here.
   ModuleDecl::ImportFilter allImportFilter = {
@@ -290,7 +291,7 @@ static void printImports(raw_ostream &out,
     M->getMissingImportedModules(allImports);
 
   ImportedModule::removeDuplicates(allImports);
-  diagnoseScopedImports(M->getASTContext().Diags, allImports);
+  diagnoseScopedImports(ctx.Diags, allImports);
 
   // Collect the public imports as a subset so that we can mark them with
   // '@_exported'.
@@ -310,7 +311,7 @@ static void printImports(raw_ostream &out,
     // 'import Builtin' in the interface. '-parse-stdlib' still implicitly
     // imports it however...
     if (importedModule->isBuiltinModule() &&
-        !M->getASTContext().LangOpts.hasFeature(Feature::BuiltinModule)) {
+        !ctx.LangOpts.hasFeature(Feature::BuiltinModule)) {
       continue;
     }
 
@@ -348,7 +349,7 @@ static void printImports(raw_ostream &out,
         out << "@_spi(" << spiName << ") ";
     }
 
-    if (M->getASTContext().LangOpts.isSwiftVersionAtLeast(6)) {
+    if (ctx.LangOpts.hasFeature(Feature::InternalImportsByDefault)) {
       out << "public ";
     }
 

lib/Sema/TypeCheckAccess.cpp

@@ -2452,7 +2452,7 @@ void swift::diagnoseUnnecessaryPublicImports(SourceFile &SF) {
 
       if (levelUsed == AccessLevel::Package) {
         inFlight.fixItReplace(import.accessLevelRange, "package");
-      } else if (ctx.isSwiftVersionAtLeast(6)) {
+      } else if (ctx.LangOpts.hasFeature(Feature::InternalImportsByDefault)) {
         // Let it default to internal.
         inFlight.fixItRemove(import.accessLevelRange);
       } else {

lib/Sema/TypeCheckAttr.cpp

@@ -999,6 +999,7 @@ bool AttributeChecker::visitAbstractAccessControlAttr(
   SourceFile *File = D->getDeclContext()->getParentSourceFile();
   if (auto importDecl = dyn_cast<ImportDecl>(D)) {
     if (!D->getASTContext().LangOpts.hasFeature(Feature::AccessLevelOnImport) &&
+        !D->getASTContext().LangOpts.hasFeature(Feature::InternalImports) &&
         File && File->Kind != SourceFileKind::Interface) {
       diagnoseAndRemoveAttr(attr, diag::access_level_on_import_not_enabled);
       return true;

lib/Sema/TypeChecker.cpp

@@ -310,7 +310,7 @@ TypeCheckSourceFileRequest::evaluate(Evaluator &eval, SourceFile *SF) const {
       CheckInconsistentSPIOnlyImportsRequest{SF},
       {});
 
-  if (!Ctx.LangOpts.isSwiftVersionAtLeast(6)) {
+  if (!Ctx.LangOpts.hasFeature(Feature::InternalImportsByDefault)) {
     evaluateOrDefault(
       Ctx.evaluator,
       CheckInconsistentAccessLevelOnImport{SF},

test/ModuleInterface/access-level-import-swiftinterfaces.swift

@@ -1,5 +1,6 @@
 /// Check that only public imports are printed in modules interfaces,
 /// package imports and below are not.
+// REQUIRES: asserts
 
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
@@ -28,8 +29,8 @@
 // RUN: %target-swift-typecheck-module-from-interface(%t/Client.private.swiftinterface) -I %t \
 // RUN:   -module-name Client
 
-// RUN: %FileCheck %s < %t/Client.swiftinterface
-// RUN: %FileCheck %s < %t/Client.private.swiftinterface
+// RUN: %FileCheck --check-prefixes=CHECK,CHECK-5 %s < %t/Client.swiftinterface
+// RUN: %FileCheck --check-prefixes=CHECK,CHECK-5 %s < %t/Client.private.swiftinterface
 
 /// Build a client composed of many files.
 // RUN: %target-swift-frontend -typecheck %t/MultiFiles?.swift -I %t \
@@ -43,8 +44,37 @@
 // RUN: %target-swift-typecheck-module-from-interface(%t/MultiFiles.private.swiftinterface) -I %t \
 // RUN:   -module-name MultiFiles
 
-// RUN: %FileCheck %s < %t/MultiFiles.swiftinterface
-// RUN: %FileCheck %s < %t/MultiFiles.private.swiftinterface
+// RUN: %FileCheck --check-prefixes=CHECK,CHECK-5 %s < %t/MultiFiles.swiftinterface
+// RUN: %FileCheck --check-prefixes=CHECK,CHECK-5 %s < %t/MultiFiles.private.swiftinterface
+
+/// Swift 6 mode.
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   -package-name TestPackage -module-name Client_Swift6 \
+// RUN:   -enable-library-evolution -swift-version 6 \
+// RUN:   -emit-module-interface-path %t/Client_Swift6.swiftinterface \
+// RUN:   -emit-private-module-interface-path %t/Client_Swift6.private.swiftinterface
+
+// RUN: %target-swift-typecheck-module-from-interface(%t/Client_Swift6.swiftinterface) -I %t
+// RUN: %target-swift-typecheck-module-from-interface(%t/Client_Swift6.private.swiftinterface) -I %t \
+// RUN:   -module-name Client_Swift6
+
+// RUN: %FileCheck %s --check-prefixes=CHECK,CHECK-6 < %t/Client_Swift6.swiftinterface
+// RUN: %FileCheck %s --check-prefixes=CHECK,CHECK-6 < %t/Client_Swift6.private.swiftinterface
+
+/// Feature flag.
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   -package-name TestPackage -module-name Client_FeatureFlag \
+// RUN:   -enable-library-evolution -swift-version 5 \
+// RUN:   -emit-module-interface-path %t/Client_FeatureFlag.swiftinterface \
+// RUN:   -emit-private-module-interface-path %t/Client_FeatureFlag.private.swiftinterface \
+// RUN:   -enable-upcoming-feature InternalImportsByDefault
+
+// RUN: %target-swift-typecheck-module-from-interface(%t/Client_FeatureFlag.swiftinterface) -I %t
+// RUN: %target-swift-typecheck-module-from-interface(%t/Client_FeatureFlag.private.swiftinterface) -I %t \
+// RUN:   -module-name Client_FeatureFlag
+
+// RUN: %FileCheck %s --check-prefixes=CHECK,CHECK-6,CHECK-FLAG < %t/Client_FeatureFlag.swiftinterface
+// RUN: %FileCheck %s --check-prefixes=CHECK,CHECK-6,CHECK-FLAG < %t/Client_FeatureFlag.private.swiftinterface
 
 //--- PublicLib.swift
 //--- PackageLib.swift
@@ -53,6 +83,10 @@
 //--- PrivateLib.swift
 
 //--- Client.swift
+// CHECK-5-NOT: public
+// CHECK-FLAG: -enable-upcoming-feature InternalImportsByDefault
+// CHECK-6: public
+
 public import PublicLib
 // CHECK: PublicLib
 

test/Sema/access-level-import-flag-check.swift

@@ -19,6 +19,9 @@
 // RUN: %target-swift-frontend -typecheck %t/ClientWithoutTheFlag.swift -I %t \
 // RUN:   -enable-experimental-feature AccessLevelOnImport \
 // RUN:   -package-name package
+// RUN: %target-swift-frontend -typecheck %t/ClientWithoutTheFlag.swift -I %t \
+// RUN:   -enable-upcoming-feature InternalImportsByDefault \
+// RUN:   -package-name package
 // REQUIRES: asserts
 
 /// swiftinterfaces don't need the flag.

test/Sema/access-level-import-inconsistencies.swift

@@ -62,6 +62,8 @@ package import Lib // expected-note {{imported 'package' here}} @:1
 
 // RUN: %target-swift-frontend -typecheck %t/ManyFiles_AmbiguitySwift6_File?.swift -I %t \
 // RUN:   -enable-experimental-feature AccessLevelOnImport -verify -swift-version 6
+// RUN: %target-swift-frontend -typecheck %t/ManyFiles_AmbiguitySwift6_File?.swift -I %t \
+// RUN:   -enable-upcoming-feature InternalImportsByDefault -verify
 //--- ManyFiles_AmbiguitySwift6_FileA.swift
 import Lib
 //--- ManyFiles_AmbiguitySwift6_FileB.swift