[Sema] Update diagnostic about public imports of non-resilient modules

The compiler reports public imports of non-resilient modules from a
resilient module. Make sure that when imports default to internal, which
also implies Swift 6, this is treated as an error and the fixit simply
deletes the `public` keyword.

We keep using the AccessLevelOnImport flag only to report these as
errors in Swift 5 for early adopters.

Author: xymus

lib/Sema/ImportResolution.cpp

@@ -821,14 +821,21 @@ void UnboundImport::validateResilience(NullablePtr<ModuleDecl> topLevelModule,
                                      topLevelModule.get()->getName(),
                                      SF.getParentModule()->getName());
 
-  if (ctx.LangOpts.hasFeature(Feature::AccessLevelOnImport)) {
+  if (ctx.LangOpts.hasFeature(Feature::InternalImportsByDefault)) {
+    // This will catch Swift 6 language mode as well where
+    // it will be reported as an error.
+    inFlight.fixItRemove(import.accessLevelRange);
+  } else {
     SourceRange attrRange = import.accessLevelRange;
     if (attrRange.isValid())
       inFlight.fixItReplace(attrRange, "internal");
     else
       inFlight.fixItInsert(import.importLoc, "internal ");
-  } else {
-    inFlight.limitBehavior(DiagnosticBehavior::Warning);
+
+    // Downgrade to warning only in pre-Swift 6 mode and
+    // when not using the experimental flag.
+    if (!ctx.LangOpts.hasFeature(Feature::AccessLevelOnImport))
+      inFlight.limitBehavior(DiagnosticBehavior::Warning);
   }
 }
 

test/Sema/access-level-and-non-resilient-import.swift

@@ -2,7 +2,7 @@
 /// a non-resilient module.
 
 // RUN: %empty-directory(%t)
-// RUN: split-file %s %t
+// RUN: split-file --leading-lines %s %t
 
 // REQUIRES: asserts
 
@@ -15,14 +15,18 @@
 // RUN: %target-swift-frontend -emit-module %t/PrivateLib.swift -o %t
 
 /// A resilient client will error on public imports.
+/// Keep AccessLevelOnImport to get the error from Swift 6 in Swift 5.
 // RUN: %target-swift-frontend -typecheck %t/Client_Swift5.swift -I %t \
 // RUN:   -enable-library-evolution -swift-version 5 \
 // RUN:   -enable-experimental-feature AccessLevelOnImport -verify \
 // RUN:   -package-name pkg
 // RUN: %target-swift-frontend -typecheck %t/Client_Swift6.swift -I %t \
-// RUN:   -enable-library-evolution -swift-version 6 \
-// RUN:   -enable-experimental-feature AccessLevelOnImport -verify \
+// RUN:   -enable-library-evolution -swift-version 6 -verify \
 // RUN:   -package-name pkg
+// RUN: %target-swift-frontend -typecheck %t/Client_Swift6.swift -I %t \
+// RUN:   -enable-library-evolution \
+// RUN:   -enable-upcoming-feature InternalImportsByDefault \
+// RUN:   -verify -package-name pkg
 
 /// A non-resilient client doesn't complain.
 // RUN: %target-swift-frontend -typecheck %t/Client_Swift5.swift -I %t \
@@ -31,7 +35,9 @@
 // RUN:   -package-name pkg
 // RUN: %target-swift-frontend -typecheck %t/Client_Swift6.swift -I %t \
 // RUN:   -swift-version 6 \
-// RUN:   -enable-experimental-feature AccessLevelOnImport \
+// RUN:   -package-name pkg
+// RUN: %target-swift-frontend -typecheck %t/Client_Swift6.swift -I %t \
+// RUN:   -enable-upcoming-feature InternalImportsByDefault \
 // RUN:   -package-name pkg
 
 //--- DefaultLib.swift
@@ -55,7 +61,7 @@ private import PrivateLib
 //--- Client_Swift6.swift
 
 import DefaultLib
-public import PublicLib // expected-error {{module 'PublicLib' was not compiled with library evolution support; using it means binary compatibility for 'Client_Swift6' can't be guaranteed}} {{1-7=internal}}
+public import PublicLib // expected-error {{module 'PublicLib' was not compiled with library evolution support; using it means binary compatibility for 'Client_Swift6' can't be guaranteed}} {{1-8=}}
 // expected-warning @-1 {{public import of 'PublicLib' was not used in public declarations or inlinable code}}
 package import PackageLib
 // expected-warning @-1 {{package import of 'PackageLib' was not used in package declarations}}