[Sema] Generalize isImplementationOnlyImported

Renaming isImportedImplementationOnly to getRestrictedImportKind will
allow us to support different kind of restrictive imports in the next
commits.

Author: xymus

include/swift/AST/SourceFile.h

@@ -25,6 +25,15 @@ namespace swift {
 
 class PersistentParserState;
 
+/// Kind of import affecting how a decl can be reexported.
+/// This is a subset of \c DisallowedOriginKind.
+///
+/// \sa getRestrictedImportKind
+enum class RestrictedImportKind {
+  ImplementationOnly,
+  None // No restriction, i.e. the module is imported publicly.
+};
+
 /// A file containing Swift source code.
 ///
 /// This is a .swift or .sil file (or a virtual file, such as the contents of
@@ -336,7 +345,8 @@ class SourceFile final : public FileUnit {
   /// If not, we can fast-path module checks.
   bool hasImplementationOnlyImports() const;
 
-  bool isImportedImplementationOnly(const ModuleDecl *module) const;
+  /// Get the most permissive restriction applied to the imports of \p module.
+  RestrictedImportKind getRestrictedImportKind(const ModuleDecl *module) const;
 
   /// Find all SPI names imported from \p importedModule by this file,
   /// collecting the identifiers in \p spiGroups.

lib/AST/Module.cpp

@@ -2438,12 +2438,7 @@ bool SourceFile::hasTestableOrPrivateImport(
       });
 }
 
-bool SourceFile::isImportedImplementationOnly(const ModuleDecl *module) const {
-  // Implementation-only imports are (currently) always source-file-specific,
-  // so if we don't have any, we know the search is complete.
-  if (!hasImplementationOnlyImports())
-    return false;
-
+RestrictedImportKind SourceFile::getRestrictedImportKind(const ModuleDecl *module) const {
   auto &imports = getASTContext().getImportCache();
 
   // Look at the imports of this source file.
@@ -2455,11 +2450,14 @@ bool SourceFile::isImportedImplementationOnly(const ModuleDecl *module) const {
     // If the module is imported this way, it's not imported
     // implementation-only.
     if (imports.isImportedBy(module, desc.module.importedModule))
-      return false;
+      return RestrictedImportKind::None;
   }
 
   // Now check this file's enclosing module in case there are re-exports.
-  return !imports.isImportedBy(module, getParentModule());
+  if (imports.isImportedBy(module, getParentModule()))
+    return RestrictedImportKind::None;
+
+  return RestrictedImportKind::ImplementationOnly;
 }
 
 bool ModuleDecl::isImportedImplementationOnly(const ModuleDecl *module) const {

lib/Sema/TypeCheckAccess.cpp

@@ -1503,7 +1503,9 @@ swift::getDisallowedOriginKind(const Decl *decl,
   downgradeToWarning = DowngradeToWarning::No;
   ModuleDecl *M = decl->getModuleContext();
   auto *SF = where.getDeclContext()->getParentSourceFile();
-  if (SF->isImportedImplementationOnly(M)) {
+
+  RestrictedImportKind howImported = SF->getRestrictedImportKind(M);
+  if (howImported != RestrictedImportKind::None) {
     // Temporarily downgrade implementation-only exportability in SPI to
     // a warning.
     if (where.isSPI())
@@ -1883,7 +1885,8 @@ class DeclAvailabilityChecker : public DeclVisitor<DeclAvailabilityChecker> {
 
     const SourceFile *SF = refDecl->getDeclContext()->getParentSourceFile();
     ModuleDecl *M = PGD->getModuleContext();
-    if (!SF->isImportedImplementationOnly(M))
+    RestrictedImportKind howImported = SF->getRestrictedImportKind(M);
+    if (howImported == RestrictedImportKind::None)
       return;
 
     auto &DE = PGD->getASTContext().Diags;

lib/Sema/TypeCheckDeclOverride.cpp

@@ -2332,7 +2332,7 @@ void swift::checkImplementationOnlyOverride(const ValueDecl *VD) {
   assert(SF && "checking a non-source declaration?");
 
   ModuleDecl *M = overridden->getModuleContext();
-  if (SF->isImportedImplementationOnly(M)) {
+  if (SF->getRestrictedImportKind(M) == RestrictedImportKind::ImplementationOnly) {
     VD->diagnose(diag::implementation_only_override_import_without_attr,
                  overridden->getDescriptiveKind())
         .fixItInsert(VD->getAttributeInsertionLoc(false),