Import lightweight Objective-C generics as Swift generic type

parameters.

Author: cwillmor

include/swift/AST/DiagnosticsSema.def

@@ -1013,6 +1013,8 @@ WARNING(non_trailing_closure_before_default_args,none,
 // Extensions
 ERROR(non_nominal_extension,none,
       "non-nominal type %0 cannot be extended", (Type))
+ERROR(extension_of_objc_generic_class,none,
+      "generic Objective-C class %0 cannot be extended", (Identifier))
 ERROR(extension_access_with_conformances,none,
       "%0 modifier cannot be used with extensions that declare "
       "protocol conformances", (DeclAttribute))
@@ -1438,6 +1440,8 @@ NOTE(class_here,none,
      "class %0 declared here", (Identifier))
 ERROR(inheritance_from_final_class,none,
 "inheritance from a final class %0", (Identifier))
+ERROR(inheritance_from_objc_generic_class,none,
+"inheritance from a generic Objective-C class %0", (Identifier))
 
 
 // Enums

include/swift/Basic/LangOptions.h

@@ -158,6 +158,10 @@ namespace swift {
     /// This is only queried when \c OmitNeedlessWords is true.
     bool StripNSPrefix = false;
 
+    /// Whether classes with Objective-C lightweight generic type parameters
+    /// should be imported into Swift as generic classes.
+    bool ImportObjCGenerics = false;
+
     /// Enable the Swift 3 migration via Fix-Its.
     bool Swift3Migration = false;
 

include/swift/Option/FrontendOptions.td

@@ -228,6 +228,10 @@ def enable_omit_needless_words :
   Flag<["-"], "enable-omit-needless-words">,
   HelpText<"Omit needless words when importing Objective-C names">;
 
+def enable_import_objc_generics :
+  Flag<["-"], "enable-import-objc-generics">,
+  HelpText<"Import Objective-C lightweight generic type params">;
+
 def enable_strip_ns_prefix :
   Flag<["-"], "enable-strip-ns-prefix">,
   HelpText<"Strip 'NS' prefix from Foundation entities">;

lib/ClangImporter/ClangImporter.cpp

@@ -2763,6 +2763,20 @@ bool ClangImporter::Implementation::shouldSuppressDeclImport(
   return false;
 }
 
+bool
+ClangImporter::Implementation::shouldSuppressGenericParamsImport(
+    const clang::ObjCInterfaceDecl *decl) {
+  while (decl) {
+    StringRef name = decl->getName();
+    if (name == "NSArray" || name == "NSDictionary" || name == "NSSet" ||
+        name == "NSOrderedSet" || name == "NSEnumerator") {
+      return true;
+    }
+    decl = decl->getSuperClass();
+  }
+  return false;
+}
+
 bool
 ClangImporter::Implementation::isAccessibilityDecl(const clang::Decl *decl) {