[Sema] Report use of conformances from non-public imports in inlinable code

Conformances imported as non-public cannot be used in API or inlinable
code, report it as an error.

Author: xymus

include/swift/AST/DiagnosticsSema.def

@@ -3461,7 +3461,8 @@ ERROR(conformance_from_implementation_only_module,none,
       "the conformance is declared as SPI|"
       "%3 was imported for SPI only|"
       "%3 was not imported by this file|"
-      "C++ types from imported module %3 do not support library evolution}4",
+      "C++ types from imported module %3 do not support library evolution|"
+      "%3 was not imported publicly}4",
       (Type, Identifier, unsigned, Identifier, unsigned))
 NOTE(assoc_conformance_from_implementation_only_module,none,
      "in associated type %0 (inferred as %1)", (Type, Type))

lib/Sema/ResilienceDiagnostics.cpp

@@ -290,7 +290,8 @@ TypeChecker::diagnoseConformanceExportability(SourceLoc loc,
                      static_cast<unsigned>(originKind))
       .warnUntilSwiftVersionIf((useConformanceAvailabilityErrorsOption &&
                                 !ctx.LangOpts.EnableConformanceAvailabilityErrors &&
-                                originKind != DisallowedOriginKind::SPIOnly) ||
+                                originKind != DisallowedOriginKind::SPIOnly &&
+                                originKind != DisallowedOriginKind::NonPublicImport) ||
                                originKind == DisallowedOriginKind::MissingImport,
                                6);
 

lib/Sema/TypeCheckAccess.cpp

@@ -1909,6 +1909,13 @@ swift::getDisallowedOriginKind(const Decl *decl,
       isFragileClangNode(decl->getClangNode()))
     return DisallowedOriginKind::FragileCxxAPI;
 
+  // Report non-public import last as it can be ignored by the caller.
+  // See \c diagnoseValueDeclRefExportability.
+  auto importSource = decl->getImportAccessFrom(where.getDeclContext());
+  if (importSource.has_value() &&
+      importSource->accessLevel < AccessLevel::Public)
+    return DisallowedOriginKind::NonPublicImport;
+
   return DisallowedOriginKind::None;
 }
 

lib/Sema/TypeCheckAccess.h

@@ -47,6 +47,7 @@ enum class DisallowedOriginKind : uint8_t {
   SPIOnly,
   MissingImport,
   FragileCxxAPI,
+  NonPublicImport,
   None
 };
 

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

@@ -0,0 +1,31 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file --leading-lines %s %t
+
+/// Build the libraries.
+// RUN: %target-swift-frontend -emit-module %t/ConformanceBaseTypes.swift -o %t
+// RUN: %target-swift-frontend -emit-module %t/ConformanceDefinition.swift -o %t -I %t
+
+/// Check diagnostics.
+// RUN: %target-swift-frontend -typecheck -verify %t/Client.swift -I %t \
+// RUN:   -enable-experimental-feature AccessLevelOnImport
+
+//--- ConformanceBaseTypes.swift
+public protocol Proto {}
+public struct ConformingType {
+    public init () {}
+}
+
+//--- ConformanceDefinition.swift
+import ConformanceBaseTypes
+extension ConformingType : Proto  {}
+
+//--- Client.swift
+public import ConformanceBaseTypes
+internal import ConformanceDefinition
+
+public func useInAPI(a: any Proto = ConformingType()) { // expected-error {{cannot use conformance of 'ConformingType' to 'Proto' here; 'ConformanceDefinition' was not imported publicly}}
+}
+
+@inlinable public func inlinableFunc() {
+  let _: any Proto = ConformingType() // expected-error {{cannot use conformance of 'ConformingType' to 'Proto' here; 'ConformanceDefinition' was not imported publicly}}
+}