[PrintAsObjC] Forward-declare bridged types

The initial pass through a type’s members to forward-declare or import anything needed by them did not account for _ObjectiveCBridgeable conformances; instead, it would examine the Swift type being bridged from, either tripping an assertion or just failing to do anything. Treat these as references to the bridged type instead.

Fixes rdar://67263753.

Author: beccadax

lib/PrintAsObjC/DeclAndTypePrinter.cpp

@@ -1339,6 +1339,7 @@ class DeclAndTypePrinter::Implementation
     return true;
   }
 
+public:
   /// If \p nominal is bridged to an Objective-C class (via a conformance to
   /// _ObjectiveCBridgeable), return that class.
   ///
@@ -1369,6 +1370,7 @@ class DeclAndTypePrinter::Implementation
     return objcType->getClassOrBoundGenericClass();
   }
 
+private:
   /// If the nominal type is bridged to Objective-C (via a conformance
   /// to _ObjectiveCBridgeable), print the bridged type.
   void printObjCBridgeableType(const NominalTypeDecl *swiftNominal,
@@ -2067,6 +2069,14 @@ bool DeclAndTypePrinter::isEmptyExtensionDecl(const ExtensionDecl *ED) {
   return getImpl().isEmptyExtensionDecl(ED);
 }
 
+const TypeDecl *DeclAndTypePrinter::getObjCTypeDecl(const TypeDecl* TD) {
+  if (auto *nominal = dyn_cast<NominalTypeDecl>(TD))
+    if (auto *bridged = getImpl().getObjCBridgedClass(nominal))
+      return bridged;
+
+  return TD;
+}
+
 StringRef
 DeclAndTypePrinter::maybeGetOSObjectBaseName(const clang::NamedDecl *decl) {
   StringRef name = decl->getName();

lib/PrintAsObjC/DeclAndTypePrinter.h

@@ -73,6 +73,14 @@ class DeclAndTypePrinter {
   /// Is \p ED empty of members and protocol conformances to include?
   bool isEmptyExtensionDecl(const ExtensionDecl *ED);
 
+  /// Returns the type that will be printed by PrintAsObjC for a parameter or
+  /// result type resolved to this declaration.
+  ///
+  /// \warning This handles \c _ObjectiveCBridgeable types, but it doesn't
+  /// currently know about other aspects of PrintAsObjC behavior, like known
+  /// types.
+  const TypeDecl *getObjCTypeDecl(const TypeDecl* TD);
+
   /// Prints a category declaring the given members.
   ///
   /// All members must have the same parent type. The list must not be empty.

lib/PrintAsObjC/ModuleContentsWriter.cpp

@@ -278,6 +278,9 @@ class ModuleWriter {
         if (TD == container)
           return;
 
+        // Bridge, if necessary.
+        TD = printer.getObjCTypeDecl(TD);
+
         if (finder.needsDefinition() && isa<NominalTypeDecl>(TD)) {
           // We can delay individual members of classes; do so if necessary.
           if (isa<ClassDecl>(container)) {

test/PrintAsObjC/classes.swift

@@ -49,8 +49,26 @@ import SingleGenericClass
 // CHECK-NEXT: @end
 @objc class B1 : A1 {}
 
+// Used in BridgedTypes test case
+struct Notification: _ObjectiveCBridgeable {
+  func _bridgeToObjectiveC() -> NSNotification { fatalError() }
+  static func _forceBridgeFromObjectiveC(
+    _ source: NSNotification,
+    result: inout Self?
+  ) { fatalError() }
+  @discardableResult
+  static func _conditionallyBridgeFromObjectiveC(
+    _ source: NSNotification,
+    result: inout Self?
+  ) -> Bool { fatalError() }
+  @_effects(readonly)
+  static func _unconditionallyBridgeFromObjectiveC(_ source: _ObjectiveCType?)
+    -> Self { fatalError() }
+}
+
 // CHECK-LABEL: @interface BridgedTypes
 // CHECK-NEXT: - (NSDictionary * _Nonnull)dictBridge:(NSDictionary * _Nonnull)x SWIFT_WARN_UNUSED_RESULT;
+// CHECK-NEXT: - (NSNotification * _Nonnull)noteBridge:(NSNotification * _Nonnull)x SWIFT_WARN_UNUSED_RESULT;
 // CHECK-NEXT: - (NSSet * _Nonnull)setBridge:(NSSet * _Nonnull)x SWIFT_WARN_UNUSED_RESULT;
 // CHECK-NEXT: init
 // CHECK-NEXT: @end
@@ -59,6 +77,10 @@ import SingleGenericClass
     return x
   }
 
+  @objc func noteBridge(_ x: Notification) -> Notification {
+    return x
+  }
+
   @objc func setBridge(_ x: Set<NSObject>) -> Set<NSObject> {
     return x
   }