[Concurrency] Print @objc async declarations as Objective-C declarations.

@objc async declarations are mapping into completion-handler-based
methods in Objective-C, so ensure that the result type, parameters,
and attributes reflect that.

Author: DougGregor

lib/PrintAsObjC/DeclAndTypePrinter.cpp

@@ -18,6 +18,7 @@
 #include "swift/AST/Comment.h"
 #include "swift/AST/Decl.h"
 #include "swift/AST/ExistentialLayout.h"
+#include "swift/AST/ForeignAsyncConvention.h"
 #include "swift/AST/ForeignErrorConvention.h"
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/PrettyStackTrace.h"
@@ -464,6 +465,7 @@ class DeclAndTypePrinter::Implementation
 
   Type getForeignResultType(AbstractFunctionDecl *AFD,
                             FunctionType *methodTy,
+                            Optional<ForeignAsyncConvention> asyncConvention,
                             Optional<ForeignErrorConvention> errorConvention) {
     // A foreign error convention can affect the result type as seen in
     // Objective-C.
@@ -484,6 +486,11 @@ class DeclAndTypePrinter::Implementation
       }
     }
 
+    // Asynchronous methods return their results via completion handler.
+    if (asyncConvention) {
+      return getASTContext().TheEmptyTupleType;
+    }
+
     auto result = methodTy->getResult();
     if (result->isUninhabited())
       return getASTContext().TheEmptyTupleType;
@@ -513,16 +520,20 @@ class DeclAndTypePrinter::Implementation
       }
     }
 
+    Optional<ForeignAsyncConvention> asyncConvention
+      = AFD->getForeignAsyncConvention();
     Optional<ForeignErrorConvention> errorConvention
       = AFD->getForeignErrorConvention();
     Type rawMethodTy = AFD->getMethodInterfaceType();
     auto methodTy = rawMethodTy->castTo<FunctionType>();
-    auto resultTy = getForeignResultType(AFD, methodTy, errorConvention);
+    auto resultTy = getForeignResultType(
+        AFD, methodTy, asyncConvention, errorConvention);
 
     // Constructors and methods returning DynamicSelf return
     // instancetype.
     if (isa<ConstructorDecl>(AFD) ||
-        (isa<FuncDecl>(AFD) && cast<FuncDecl>(AFD)->hasDynamicSelfResult())) {
+        (isa<FuncDecl>(AFD) && cast<FuncDecl>(AFD)->hasDynamicSelfResult() &&
+         !AFD->hasAsync())) {
       if (errorConvention && errorConvention->stripsResultOptionality()) {
         printNullability(OTK_Optional, NullabilityPrintKind::ContextSensitive);
       } else if (auto ctor = dyn_cast<ConstructorDecl>(AFD)) {
@@ -578,6 +589,16 @@ class DeclAndTypePrinter::Implementation
       StringRef piece = selectorPieces[i].empty() ? StringRef("")
                                                   : selectorPieces[i].str();
 
+      // If we have an async convention and this is the completion handler
+      // parameter, print it.
+      if (asyncConvention &&
+          i == asyncConvention->completionHandlerParamIndex()) {
+        os << piece << ":(";
+        print(asyncConvention->completionHandlerType(), None);
+        os << ")completionHandler";
+        continue;
+      }
+
       // If we have an error convention and this is the error
       // parameter, print it.
       if (errorConvention && i == errorConvention->getErrorParameterIndex()) {
@@ -660,7 +681,9 @@ class DeclAndTypePrinter::Implementation
       if (looksLikeInitMethod(AFD->getObjCSelector())) {
         os << " SWIFT_METHOD_FAMILY(none)";
       }
-      if (methodTy->getResult()->isUninhabited()) {
+      if (asyncConvention) {
+        // Async methods don't have result types to annotate.
+      } else if (methodTy->getResult()->isUninhabited()) {
         os << " SWIFT_NORETURN";
       } else if (!methodTy->getResult()->isVoid() &&
                  !AFD->getAttrs().hasAttribute<DiscardableResultAttr>()) {
@@ -697,12 +720,15 @@ class DeclAndTypePrinter::Implementation
 
   void printAbstractFunctionAsFunction(FuncDecl *FD) {
     printDocumentationComment(FD);
+    Optional<ForeignAsyncConvention> asyncConvention
+      = FD->getForeignAsyncConvention();
     Optional<ForeignErrorConvention> errorConvention
       = FD->getForeignErrorConvention();
     assert(!FD->getGenericSignature() &&
            "top-level generic functions not supported here");
     auto funcTy = FD->getInterfaceType()->castTo<FunctionType>();
-    auto resultTy = getForeignResultType(FD, funcTy, errorConvention);
+    auto resultTy = getForeignResultType(
+        FD, funcTy, asyncConvention, errorConvention);
 
     // The result type may be a partial function type we need to close
     // up later.

test/PrintAsObjC/async.swift

@@ -0,0 +1,30 @@
+// REQUIRES: objc_interop
+
+// RUN: %empty-directory(%t)
+
+// FIXME: BEGIN -enable-source-import hackaround
+// RUN:  %target-swift-frontend(mock-sdk: -sdk %S/../Inputs/clang-importer-sdk -I %t) -emit-module -o %t %S/../Inputs/clang-importer-sdk/swift-modules/ObjectiveC.swift -disable-objc-attr-requires-foundation-module
+// RUN:  %target-swift-frontend(mock-sdk: -sdk %S/../Inputs/clang-importer-sdk -I %t) -emit-module -o %t  %S/../Inputs/clang-importer-sdk/swift-modules/CoreGraphics.swift
+// RUN:  %target-swift-frontend(mock-sdk: -sdk %S/../Inputs/clang-importer-sdk -I %t) -emit-module -o %t  %S/../Inputs/clang-importer-sdk/swift-modules/Foundation.swift
+// RUN:  %target-swift-frontend(mock-sdk: -sdk %S/../Inputs/clang-importer-sdk -I %t) -emit-module -o %t  %S/../Inputs/clang-importer-sdk/swift-modules/AppKit.swift
+// FIXME: END -enable-source-import hackaround
+
+
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../Inputs/clang-importer-sdk -I %t) -parse-as-library %s -typecheck -I %S/Inputs/custom-modules -emit-objc-header-path %t/async.h -import-objc-header %S/../Inputs/empty.h  -enable-experimental-concurrency -typecheck
+// RUN: %FileCheck %s < %t/async.h
+// RUN: %check-in-clang -I %S/Inputs/custom-modules/ %t/async.h
+
+import Foundation
+
+// CHECK-LABEL: @interface BarClass : NSObject
+@objc @objcMembers class BarClass: NSObject {
+  // CHECK: (void)doSomethingBigWithCompletionHandler:(void (^)(NSInteger))completionHandler;
+  func doSomethingBig() async -> Int { 0 }
+
+  // CHECK: - (void)longRunningWithString:(NSString * _Nonnull)string completionHandler:(void (^)(BarClass * _Nullable, NSError * _Nullable))completionHandler;
+  func longRunning(string: String) async throws -> BarClass { return self }
+
+  // CHECK: - (void)magicTupleReturnWithCompletionHandler:(void (^)(BarClass * _Nonnull, NSInteger))completionHandler;
+  func magicTupleReturn() async -> (BarClass, Int) { return (self, 0) }
+}
+// CHECK: @end