[cxx-interop] Allow retain/release operations to return an unsigned integer

Release/retain functions for C++ foreign reference types might return a reference count as an integer value.

Swift previously emitted an error for such functions, saying that the retain/release functions need to return void or a reference to the value.

rdar://157853183

Author: egorzhdan

include/swift/AST/DiagnosticsClangImporter.def

@@ -261,11 +261,11 @@ ERROR(foreign_reference_types_invalid_retain_release, none,
 
 ERROR(foreign_reference_types_retain_non_void_or_self_return_type, none,
       "specified retain function '%0' is invalid; "
-      "retain function must have 'void' or parameter return type",
+      "retain function must either return have 'void', the reference count as an integer, or the parameter type",
       (StringRef))
 ERROR(foreign_reference_types_release_non_void_return_type, none,
       "specified release function '%0' is invalid; "
-      "release function must have 'void' return type",
+      "release function must either return 'void' or the reference count as an integer",
       (StringRef))
 ERROR(foreign_reference_types_retain_release_not_a_function_decl, none,
       "specified %select{retain|release}0 function '%1' is not a function",

lib/ClangImporter/ImportDecl.cpp

@@ -2739,7 +2739,7 @@ namespace {
 
       enum class RetainReleaseOperationKind {
         notAfunction,
-        doesntReturnVoidOrSelf,
+        invalidReturnType,
         invalidParameters,
         valid
       };
@@ -2767,10 +2767,20 @@ namespace {
         // The return type should be void (for release functions), or void
         // or the parameter type (for retain functions).
         auto resultInterfaceType = operationFn->getResultInterfaceType();
-        if (!resultInterfaceType->isVoid()) {
+        if (!resultInterfaceType->isVoid() &&
+            !resultInterfaceType->isUInt() &&
+            !resultInterfaceType->isUInt8() &&
+            !resultInterfaceType->isUInt16() &&
+            !resultInterfaceType->isUInt32() &&
+            !resultInterfaceType->isUInt64() &&
+            !resultInterfaceType->isInt() &&
+            !resultInterfaceType->isInt8() &&
+            !resultInterfaceType->isInt16() &&
+            !resultInterfaceType->isInt32() &&
+            !resultInterfaceType->isInt64()) {
           if (operationKind == CustomRefCountingOperationKind::release ||
               !resultInterfaceType->lookThroughSingleOptionalType()->isEqual(paramType))
-            return RetainReleaseOperationKind::doesntReturnVoidOrSelf;
+            return RetainReleaseOperationKind::invalidReturnType;
         }
 
         // The parameter of the retain/release function should be pointer to the
@@ -2835,7 +2845,7 @@ namespace {
               diag::foreign_reference_types_retain_release_not_a_function_decl,
               false, retainOperation.name);
           break;
-        case RetainReleaseOperationKind::doesntReturnVoidOrSelf:
+        case RetainReleaseOperationKind::invalidReturnType:
           Impl.diagnose(
               loc,
               diag::foreign_reference_types_retain_non_void_or_self_return_type,
@@ -2900,7 +2910,7 @@ namespace {
               diag::foreign_reference_types_retain_release_not_a_function_decl,
               true, releaseOperation.name);
           break;
-        case RetainReleaseOperationKind::doesntReturnVoidOrSelf:
+        case RetainReleaseOperationKind::invalidReturnType:
           Impl.diagnose(
               loc,
               diag::foreign_reference_types_release_non_void_return_type,

test/Interop/Cxx/foreign-reference/Inputs/reference-counted.h

@@ -68,6 +68,21 @@ GlobalCountNullableInit {
 
 inline void GCRetainNullableInit(GlobalCountNullableInit *x) { globalCount++; }
 inline void GCReleaseNullableInit(GlobalCountNullableInit *x) { globalCount--; }
+
+struct __attribute__((swift_attr("import_as_ref")))
+__attribute__((swift_attr("retain:RCRetain")))
+__attribute__((swift_attr("release:RCRelease"))) HasOpsReturningRefCount final {
+  int refCount = 0;
+
+  static HasOpsReturningRefCount *create() {
+    return new (malloc(sizeof(HasOpsReturningRefCount)))
+        HasOpsReturningRefCount();
+  }
+};
+
+inline unsigned RCRetain(HasOpsReturningRefCount *x) { return ++x->refCount; }
+inline unsigned RCRelease(HasOpsReturningRefCount *x) { return --x->refCount; }
+
 #endif
 
 typedef struct __attribute__((swift_attr("import_as_ref")))

test/Interop/Cxx/foreign-reference/invalid-retain-operation-errors.swift

@@ -25,7 +25,7 @@ struct
     __attribute__((swift_attr("release:badRelease")))
 BadRetainRelease {};
 
-int badRetain(BadRetainRelease *v);
+float badRetain(BadRetainRelease *v);
 void badRelease(BadRetainRelease *v, int i);
 
 struct
@@ -235,7 +235,7 @@ public func test(x: NonExistent) { }
 @available(macOS 13.3, *)
 public func test(x: NoRetainRelease) { }
 
-// CHECK: error: specified retain function 'badRetain' is invalid; retain function must have 'void' or parameter return type
+// CHECK: error: specified retain function 'badRetain' is invalid; retain function must either return have 'void', the reference count as an integer, or the parameter type
 // CHECK: error: specified release function 'badRelease' is invalid; release function must have exactly one argument of type 'BadRetainRelease'
 @available(macOS 13.3, *)
 public func test(x: BadRetainRelease) { }

test/Interop/Cxx/foreign-reference/reference-counted-irgen.swift

@@ -17,6 +17,19 @@ public func getLocalCount() -> NS.LocalCount {
 // CHECK-NEXT: }
 
 
+public func useRetainReleaseOpsReturningRefCount() -> HasOpsReturningRefCount {
+    let result = HasOpsReturningRefCount.create()
+    return result
+}
+
+// CHECK:      define {{.*}}swiftcc ptr @"$s4main36useRetainReleaseOpsReturningRefCountSo03HasefgH0VyF"()
+// CHECK-NEXT: entry:
+// CHECK:        %0 = call ptr @{{_ZN23HasOpsReturningRefCount6createEv|"\?create\@HasOpsReturningRefCount\@\@SAPEAU1\@XZ"}}()
+// CHECK:        %1 = call i32 @{{_Z8RCRetainP23HasOpsReturningRefCount|"\?RCRetain\@\@YAIPEAUHasOpsReturningRefCount\@\@\@Z"}}(ptr %0)
+// CHECK:        ret ptr %0
+// CHECK-NEXT: }
+
+
 public func get42() -> Int32 {
     let result = NS.LocalCount.create()
     return result.returns42()