[Sema] Report typealiases desugaring to a non-public import in API

Typealiases with an underlying type from a non-public import cannot be
used in API or inlinable code. Report this as an error.

Author: xymus

include/swift/AST/DiagnosticsSema.def

@@ -3450,7 +3450,8 @@ ERROR(typealias_desugars_to_type_from_hidden_module,none,
       "<<ERROR>>|"
       "%4 was imported for SPI only|"
       "%4 was not imported by this file|"
-      "C++ types from imported module %4 do not support library evolution}5",
+      "C++ types from imported module %4 do not support library evolution|"
+      "%4 was not imported publicly}5",
       (const TypeAliasDecl *, StringRef, StringRef, unsigned, Identifier, unsigned))
 ERROR(conformance_from_implementation_only_module,none,
       "cannot use conformance of %0 to %1 %select{here|as property wrapper here|"
@@ -6586,7 +6587,8 @@ ERROR(inlinable_typealias_desugars_to_type_from_hidden_module,
       "<<ERROR>>|"
       "%4 was imported for SPI only|"
       "%4 was not imported by this file|"
-      "C++ types from imported module %4 do not support library evolution}5",
+      "C++ types from imported module %4 do not support library evolution|"
+      "%4 was not imported publicly}5",
       (const TypeAliasDecl *, StringRef, StringRef, unsigned, Identifier, unsigned))
 
 NOTE(missing_import_inserted,

lib/Sema/ResilienceDiagnostics.cpp

@@ -152,24 +152,24 @@ static bool diagnoseTypeAliasDeclRefExportability(SourceLoc loc,
 
   auto definingModule = D->getModuleContext();
   auto fragileKind = where.getFragileFunctionKind();
+  bool warnPreSwift6 = originKind != DisallowedOriginKind::SPIOnly &&
+                       originKind != DisallowedOriginKind::NonPublicImport;
   if (fragileKind.kind == FragileFunctionKind::None) {
     auto reason = where.getExportabilityReason();
     ctx.Diags
         .diagnose(loc, diag::typealias_desugars_to_type_from_hidden_module,
                   TAD, definingModule->getNameStr(), D->getNameStr(),
                   static_cast<unsigned>(*reason), definingModule->getName(),
                   static_cast<unsigned>(originKind))
-        .warnUntilSwiftVersionIf(originKind != DisallowedOriginKind::SPIOnly,
-                                 6);
+        .warnUntilSwiftVersionIf(warnPreSwift6, 6);
   } else {
     ctx.Diags
         .diagnose(loc,
                   diag::inlinable_typealias_desugars_to_type_from_hidden_module,
                   TAD, definingModule->getNameStr(), D->getNameStr(),
                   fragileKind.getSelector(), definingModule->getName(),
                   static_cast<unsigned>(originKind))
-        .warnUntilSwiftVersionIf(originKind != DisallowedOriginKind::SPIOnly,
-                                 6);
+        .warnUntilSwiftVersionIf(warnPreSwift6, 6);
   }
   D->diagnose(diag::kind_declared_here, DescriptiveDeclKind::Type);
 

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

@@ -0,0 +1,32 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-emit-module-interface(%t/Original.swiftinterface) %t/Original.swift
+// RUN: %target-swift-typecheck-module-from-interface(%t/Original.swiftinterface)
+
+// RUN: %target-swift-emit-module-interface(%t/Aliases.swiftinterface) %t/Aliases.swift -I %t
+// RUN: %target-swift-typecheck-module-from-interface(%t/Aliases.swiftinterface) -I %t
+
+// RUN: %target-swift-frontend -typecheck -verify %t/UsesAliasesNoImport.swift -I %t \
+// RUN:   -swift-version 5 -enable-library-evolution \
+// RUN:   -enable-experimental-feature AccessLevelOnImport
+
+//--- Original.swift
+open class Clazz {}
+
+//--- Aliases.swift
+import Original
+public typealias ClazzAlias = Clazz
+
+//--- UsesAliasesNoImport.swift
+public import Aliases
+internal import Original
+
+// expected-error@+1 {{'ClazzAlias' aliases 'Original.Clazz' and cannot be used here because 'Original' was not imported publicly}}
+public class InheritsFromClazzAlias: ClazzAlias {}
+
+@inlinable public func inlinableFunc() {
+  // expected-error@+1 {{'ClazzAlias' aliases 'Original.Clazz' and cannot be used in an '@inlinable' function because 'Original' was not imported publicly}}
+  _ = ClazzAlias.self
+}
+