[6.1] Sema: Prioritize @_exported imports over local non-public imports

lib/AST/Module.cpp

@@ -2944,6 +2944,16 @@ SourceFile::getImportAccessLevel(const ModuleDecl *targetModule) const {
       restrictiveImport = import;
     }
   }
+
+  // Reexports from the local module take precedence over non-public imports
+  // and lift all access-level restrictions. We still prioritize file local
+  // public imports as diagnostics will have an import to point to and
+  // they are recommended over indirect imports.
+  if ((!restrictiveImport.has_value() ||
+       restrictiveImport->accessLevel < AccessLevel::Public) &&
+     imports.isImportedBy(targetModule, getParentModule()))
+    return std::nullopt;
+
   return restrictiveImport;
 }
 

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

@@ -0,0 +1,55 @@
+/// Test that an @_exported import is preferred to local non-public imports.
+// RUN: %empty-directory(%t)
+// RUN: split-file --leading-lines %s %t
+
+/// Build the libraries.
+// RUN: %target-swift-frontend -emit-module %t/TargetLib.swift -o %t
+// RUN: %target-swift-frontend -emit-module %t/IndirectLib.swift -I %t -o %t
+
+/// Check acceptable client configurations to access TargetLib publicly.
+// RUN: %target-swift-frontend -typecheck -verify -I %t \
+// RUN:   %t/Client_ImportDirect.swift
+// RUN: %target-swift-frontend -typecheck -verify -I %t \
+// RUN:   %t/Client_ImportDirect.swift %t/Client_FileReexport.swift
+// RUN: %target-swift-frontend -typecheck -verify -I %t \
+// RUN:   %t/Client_ImportDirectAsPrivate.swift %t/Client_FileReexport.swift
+// RUN: %target-swift-frontend -typecheck -verify -I %t \
+// RUN:   %t/Client_ImportIndirectModule.swift
+// RUN: %target-swift-frontend -typecheck -verify -I %t \
+// RUN:   %t/Client_ImportIndirectModule.swift %t/Client_FileReexport.swift
+// RUN: %target-swift-frontend -typecheck -verify -I %t \
+// RUN:   %t/Client_ImportIndirectModuleAsPrivate.swift %t/Client_FileReexport.swift
+// RUN: %target-swift-frontend -typecheck -verify -I %t \
+// RUN:   %t/Client_ImportIndirectLocal.swift %t/Client_FileReexport.swift
+
+//--- TargetLib.swift
+public struct TargetType {
+    public init() {}
+}
+
+//--- IndirectLib.swift
+@_exported import TargetLib
+
+//--- Client_FileReexport.swift
+@_exported public import TargetLib
+
+//--- Client_ImportDirect.swift
+public import TargetLib
+public func user(t: TargetType) {}
+
+//--- Client_ImportDirectAsPrivate.swift
+fileprivate import TargetLib
+public func user(t: TargetType) {}
+// Unrestricted as it's @_exported elsewhere in the module
+
+//--- Client_ImportIndirectModule.swift
+public import IndirectLib
+public func user(t: TargetType) {}
+
+//--- Client_ImportIndirectModuleAsPrivate.swift
+fileprivate import IndirectLib
+public func user(t: TargetType) {}
+// Unrestricted as it's @_exported elsewhere in the module
+
+//--- Client_ImportIndirectLocal.swift
+public func user(t: TargetType) {}

test/Sema/authoritative-import-priority.swift

@@ -17,11 +17,21 @@
 /// Client testing order of preference for more levels of imports.
 // RUN: %target-swift-frontend -typecheck -I %t \
 // RUN:   %t/ExportedClient_FileExported.swift %t/ExportedClient_FileA.swift \
-// RUN:   %t/ExportedClient_FileB.swift %t/ExportedClient_FileC.swift %t/ExportedClient_FileD.swift \
+// RUN:   %t/ExportedClient_FileB.swift %t/ExportedClient_FileC.swift \
+// RUN:   %t/ExportedClient_FileD_via_underlying.swift \
 // RUN:   -import-underlying-module -module-name ExportedClient \
 // RUN:   -enable-upcoming-feature InternalImportsByDefault \
 // RUN:   -Rmodule-api-import -verify
 
+// Same without the underlying clang module.
+// RUN: %target-swift-frontend -typecheck -I %t \
+// RUN:   %t/ExportedClient_FileExported.swift %t/ExportedClient_FileA.swift \
+// RUN:   %t/ExportedClient_FileB.swift %t/ExportedClient_FileC.swift \
+// RUN:   %t/ExportedClient_FileD_via_exported.swift \
+// RUN:   -module-name ExportedClient \
+// RUN:   -enable-upcoming-feature InternalImportsByDefault \
+// RUN:   -Rmodule-api-import -verify
+
 /// Client testing -public-module-name ordering.
 // RUN: %target-swift-frontend -typecheck -I %t \
 // RUN:   %t/SwiftLibClient_FileA.swift %t/SwiftLibClient_FileB.swift \
@@ -156,11 +166,16 @@ public import NotLib
 public func useTypesC(a: ExportedType) {}
 // expected-remark @-1 {{struct 'ExportedType' is imported via 'NotLib', which reexports definition from 'LibCore'}}
 
-//--- ExportedClient_FileD.swift
-/// Last used the module-wide @_exported import.
+//--- ExportedClient_FileD_via_underlying.swift
+/// Then use the import of the underling clang module.
 public func useTypesD(a: ExportedType) {}
 // expected-remark @-1 {{struct 'ExportedType' is imported via 'ExportedClient', which reexports definition from 'LibCore'}}
 
+//--- ExportedClient_FileD_via_exported.swift
+/// Finally use the @_exported import from the local module.
+public func useTypesD(a: ExportedType) {}
+// It would be nice to have a remark even without an import to point to.
+
 
 //--- SwiftLibClient_FileA.swift
 /// Prefer the import matching public-module-name.