Clang importer: Import ObjC 'id' as Swift 'Any' (behind a flag).

For experimentation purposes, add a flag to cause the Clang importer to map ObjC APIs using `id` to `Any` instead of `AnyObject`.

Author: jckarter

include/swift/Basic/LangOptions.h

@@ -157,6 +157,9 @@ namespace swift {
     /// Whether we are stripping the "NS" prefix from Foundation et al.
     bool StripNSPrefix = true;
 
+    /// Should 'id' in Objective-C be imported as 'Any' in Swift?
+    bool EnableIdAsAny = false;
+
     /// Enable the Swift 3 migration via Fix-Its.
     bool Swift3Migration = false;
 

include/swift/Option/FrontendOptions.td

@@ -347,5 +347,8 @@ def group_info_path : Separate<["-"], "group-info-path">,
 
 def enable_protocol_typealiases: Flag<["-"], "enable-protocol-typealiases">,
   HelpText<"Enable typealiases inside protocol declarations">;
+  
+def enable_id_as_any: Flag<["-"], "enable-id-as-any">,
+  HelpText<"Enable importing ObjC 'id' as Swift 'Any' type">;
 
 } // end let Flags = [FrontendOption, NoDriverOption, HelpHidden]

lib/ClangImporter/ImportDecl.cpp

@@ -1500,6 +1500,16 @@ namespace {
 
       Type SwiftType;
       if (Decl->getDeclContext()->getRedeclContext()->isTranslationUnit()) {
+        // Ignore the 'id' typedef. We want to bridge the underlying
+        // ObjCId type.
+        //
+        // When we remove the EnableIdAsAny staging flag, the 'id' entry
+        // should be removed from MappedTypes.def, and this conditional should
+        // become unnecessary.
+        if (Name.str() == "id" && Impl.SwiftContext.LangOpts.EnableIdAsAny) {
+          return nullptr;
+        }
+      
         bool IsError;
         StringRef StdlibTypeName;
         MappedTypeNameKind NameMapping;

lib/ClangImporter/ImportType.cpp

@@ -926,9 +926,15 @@ namespace {
       if (!proto)
         return Type();
 
-      // id maps to AnyObject.
+      // id maps to Any in bridgeable contexts, AnyObject otherwise.
       if (type->isObjCIdType()) {
-        return { proto->getDeclaredType(), ImportHint::ObjCPointer };
+        if (Impl.SwiftContext.LangOpts.EnableIdAsAny) {
+          return { proto->getDeclaredType(),
+                 ImportHint(ImportHint::ObjCBridged,
+                         ProtocolCompositionType::get(Impl.SwiftContext, {})) };
+        } else {
+          return { proto->getDeclaredType(), ImportHint::ObjCPointer };
+        }
       }
 
       // Class maps to AnyObject.Type.

lib/Frontend/CompilerInvocation.cpp

@@ -776,6 +776,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
 
   Opts.EnableThrowWithoutTry |= Args.hasArg(OPT_enable_throw_without_try);
   Opts.EnableProtocolTypealiases |= Args.hasArg(OPT_enable_protocol_typealiases);
+  Opts.EnableIdAsAny |= Args.hasArg(OPT_enable_id_as_any);
 
   if (auto A = Args.getLastArg(OPT_enable_objc_attr_requires_foundation_module,
                                OPT_disable_objc_attr_requires_foundation_module)) {

test/ClangModules/objc_id_as_any.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -parse -verify -enable-id-as-any %s
+// REQUIRES: objc_interop
+
+import Foundation
+
+func assertTypeIsAny(_: Any.Protocol) {}
+func staticType<T>(_: T) -> T.Type { return T.self }
+
+let idLover = IdLover()
+
+let t1 = staticType(idLover.makesId())
+assertTypeIsAny(t1)
+
+struct ArbitraryThing {}
+idLover.takesId(ArbitraryThing())
+
+var x: AnyObject = NSObject()
+idLover.takesArray(ofId: &x)
+var y: Any = NSObject()
+idLover.takesArray(ofId: &y) // expected-error{{}}

test/Inputs/clang-importer-sdk/usr/include/Foundation.h

@@ -1034,6 +1034,14 @@ extern NSString *NSHTTPRequestKey;
 
 @end
 
+@interface NSIdLover: NSObject
+
+- (id _Nonnull)makesId;
+- (void)takesId:(id _Nonnull)x;
+- (void)takesArrayOfId:(const id _Nonnull * _Nonnull)x;
+
+@end
+
 #define NSTimeIntervalSince1970 978307200.0
 #define NS_DO_SOMETHING 17