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[cxx-interop] Add SWIFT_RETURNS_RETAINED and SWIFT_RETURNS_UNRETAINED annotations to specify ownership of FRT returned by a C++ method or function
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‎include/swift/AST/DiagnosticsClangImporter.def

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Original file line numberDiff line numberDiff line change
@@ -248,6 +248,9 @@ ERROR(failed_base_method_call_synthesis,none,
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"failed to synthesize call to the base method %0 of type %0",
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(ValueDecl *, ValueDecl *))
250250

251+
ERROR(both_returns_retained_returns_unretained,none,
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"%0 cannot be annotated with both swift_attr('returns_retained') and swift_attr('returns_unretained') attributes", (const clang::NamedDecl*))
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251254
NOTE(unsupported_builtin_type, none, "built-in type '%0' not supported", (StringRef))
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NOTE(record_field_not_imported, none, "field %0 unavailable (cannot import)", (const clang::NamedDecl*))
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NOTE(invoked_func_not_imported, none, "function %0 unavailable (cannot import)", (const clang::NamedDecl*))

‎lib/ClangImporter/ImportDecl.cpp

Lines changed: 22 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3256,6 +3256,28 @@ namespace {
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return property->getParsedAccessor(AccessorKind::Set);
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}
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// Emit error if a decl is annotated with both
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// swift_attr("returns_retained") and swift_attr("returns_unretained")
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if (decl->hasAttrs()) {
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bool returnsRetainedAttrIsPresent = false;
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bool returnsUnretainedAttrIsPresent = false;
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for (const auto *attr : decl->getAttrs()) {
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if (const auto *swiftAttr = dyn_cast<clang::SwiftAttrAttr>(attr)) {
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if (swiftAttr->getAttribute() == "returns_unretained") {
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returnsUnretainedAttrIsPresent = true;
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} else if (swiftAttr->getAttribute() == "returns_retained") {
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returnsRetainedAttrIsPresent = true;
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}
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}
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}
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if (returnsRetainedAttrIsPresent && returnsUnretainedAttrIsPresent) {
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HeaderLoc loc(decl->getLocation());
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Impl.diagnose(loc, diag::both_returns_retained_returns_unretained,
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decl);
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}
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}
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32593281
return importFunctionDecl(decl, importedName, correctSwiftName,
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std::nullopt);
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}

‎lib/ClangImporter/SwiftBridging/swift/bridging

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Original file line numberDiff line numberDiff line change
@@ -158,6 +158,13 @@
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#define SWIFT_NONCOPYABLE \
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__attribute__((swift_attr("~Copyable")))
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/// Specifies the ownership semantics (passed as owned/retained or
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/// unowned/unretained) for C++ free/global functions and static methods having
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/// a FRT as return type.
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#define SWIFT_RETURNS_RETAINED __attribute__((swift_attr("returns_retained")))
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#define SWIFT_RETURNS_UNRETAINED \
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__attribute__((swift_attr("returns_unretained")))
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#else // #if _CXX_INTEROP_HAS_ATTRIBUTE(swift_attr)
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// Empty defines for compilers that don't support `attribute(swift_attr)`.
@@ -172,6 +179,8 @@
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#define SWIFT_MUTATING
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#define SWIFT_UNCHECKED_SENDABLE
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#define SWIFT_NONCOPYABLE
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#define SWIFT_RETURNS_RETAINED
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#define SWIFT_RETURNS_UNRETAINED
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#endif // #if _CXX_INTEROP_HAS_ATTRIBUTE(swift_attr)
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‎lib/SIL/IR/SILFunctionType.cpp

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Original file line numberDiff line numberDiff line change
@@ -3423,6 +3423,26 @@ class CFunctionTypeConventions : public Conventions {
34233423
const clang::FunctionType *type)
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: Conventions(kind), FnType(type) {}
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// Helper function to return ResultConvention if the decl has either
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// swift_attr("returns_retained") or ("returns_unretained") attribute.
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std::optional<ResultConvention>
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getResultConventionWithAttributes(const TypeLowering &tl,
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const clang::FunctionDecl *decl) const {
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if (tl.getLoweredType().isForeignReferenceType() && decl->hasAttrs()) {
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for (const auto *attr : decl->getAttrs()) {
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if (const auto *swiftAttr = dyn_cast<clang::SwiftAttrAttr>(attr)) {
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if (swiftAttr->getAttribute() == "returns_unretained") {
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return ResultConvention::Unowned;
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} else if (swiftAttr->getAttribute() == "returns_retained") {
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return ResultConvention::Owned;
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}
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}
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}
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}
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return std::nullopt; // Return an empty optional if no matching attribute is
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// found
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}
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34263446
public:
34273447
CFunctionTypeConventions(const clang::FunctionType *type)
34283448
: Conventions(ConventionsKind::CFunctionType), FnType(type) {}
@@ -3540,6 +3560,13 @@ class CFunctionConventions : public CFunctionTypeConventions {
35403560
return ResultConvention::Indirect;
35413561
}
35423562

3563+
// Explicitly setting the ownership of the returned FRT if the C++
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// global/free function has either swift_attr("returns_retained") or
3565+
// ("returns_unretained") attribute.
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if (auto resultConventionOpt =
3567+
getResultConventionWithAttributes(tl, TheDecl))
3568+
return *resultConventionOpt;
3569+
35433570
if (isCFTypedef(tl, TheDecl->getReturnType())) {
35443571
// The CF attributes aren't represented in the type, so we need
35453572
// to check them here.
@@ -3618,6 +3645,14 @@ class CXXMethodConventions : public CFunctionTypeConventions {
36183645
// possible to make it easy for LLVM to optimize away the thunk.
36193646
return ResultConvention::Indirect;
36203647
}
3648+
3649+
// Explicitly setting the ownership of the returned FRT if the C++ member
3650+
// method has either swift_attr("returns_retained") or
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// ("returns_unretained") attribute.
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if (auto resultConventionOpt =
3653+
getResultConventionWithAttributes(resultTL, TheDecl))
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return *resultConventionOpt;
3655+
36213656
if (TheDecl->hasAttr<clang::CFReturnsRetainedAttr>() &&
36223657
resultTL.getLoweredType().isForeignReferenceType()) {
36233658
return ResultConvention::Owned;

‎test/Interop/Cxx/foreign-reference/Inputs/cxx-functions-and-methods-returning-frt.h

Lines changed: 94 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,94 @@
1+
#pragma once
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// FRT or SWIFT_SHARED_REFERENCE type
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struct FRTStruct {
5+
} \
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__attribute__((swift_attr("import_reference"))) \
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__attribute__((swift_attr("retain:retainFRTStruct"))) \
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__attribute__((swift_attr("release:releaseFRTStruct")));
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// Retain function for the FRT or SWIFT_SHARED_REFERENCE type FRTStruct
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void retainFRTStruct(FRTStruct * _Nonnull b) {
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}
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// Release function for the FRT or SWIFT_SHARED_REFERENCE type FRTStruct
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void releaseFRTStruct(FRTStruct * _Nonnull b) {
16+
}
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// Global/free C++ functions returning FRT without any attributes
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FRTStruct* _Nonnull global_function_returning_FRT();
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FRTStruct* _Nonnull global_function_returning_copy();
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FRTStruct* _Nonnull global_function_returning_create();
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FRTStruct* _Nonnull global_function_returning_init();
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FRTStruct* _Nonnull global_function_returning_clone();
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// Global/free C++ functions returning FRT with attribute swift_attr("returns_retained") or SWIFT_RETURNS_RETAINED
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FRTStruct* _Nonnull global_function_returning_FRT_with_attr_returns_retained() __attribute__((swift_attr("returns_retained")));
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FRTStruct* _Nonnull global_function_returning_copy_with_attr_returns_retained() __attribute__((swift_attr("returns_retained")));
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FRTStruct* _Nonnull global_function_returning_create_with_attr_returns_retained() __attribute__((swift_attr("returns_retained")));
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FRTStruct* _Nonnull global_function_returning_init_with_attr_returns_retained() __attribute__((swift_attr("returns_retained")));
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FRTStruct* _Nonnull global_function_returning_clone_with_attr_returns_retained() __attribute__((swift_attr("returns_retained")));
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// Global/free C++ functions returning FRT with attribute swift_attr("returns_unretained") or SWIFT_RETURNS_UNRETAINED
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FRTStruct* _Nonnull global_function_returning_FRT_with_attr_returns_unretained() __attribute__((swift_attr("returns_unretained")));
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FRTStruct* _Nonnull global_function_returning_copy_with_attr_returns_unretained() __attribute__((swift_attr("returns_unretained")));
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FRTStruct* _Nonnull global_function_returning_create_with_attr_returns_unretained() __attribute__((swift_attr("returns_unretained")));
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FRTStruct* _Nonnull global_function_returning_init_with_attr_returns_unretained() __attribute__((swift_attr("returns_unretained")));
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FRTStruct* _Nonnull global_function_returning_clone_with_attr_returns_unretained() __attribute__((swift_attr("returns_unretained")));
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// Struct having static methods returning FRT without any attributes
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struct StructWithStaticMethodsReturningFRTWithoutAttributes {
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static FRTStruct* _Nonnull StaticMethodReturningFRT();
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static FRTStruct* _Nonnull StaticMethodReturningFRT_copy();
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static FRTStruct* _Nonnull StaticMethodReturningFRT_create();
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static FRTStruct* _Nonnull StaticMethodReturningFRT_init();
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static FRTStruct* _Nonnull StaticMethodReturningFRT_clone();
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};
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// Struct having static methods returning FRT with attribute swift_attr("returns_retained") or SWIFT_RETURNS_RETAINED
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struct StructWithStaticMethodsReturningFRTWithAttributeReturnsRetained {
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static FRTStruct* _Nonnull StaticMethodReturningFRT() __attribute__((swift_attr("returns_retained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_copy() __attribute__((swift_attr("returns_retained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_create() __attribute__((swift_attr("returns_retained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_init() __attribute__((swift_attr("returns_retained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_clone() __attribute__((swift_attr("returns_retained")));
55+
};
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// Struct having static methods returning FRT with attribute swift_attr("returns_unretained") or SWIFT_RETURNS_UNRETAINED
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struct StructWithStaticMethodsReturningFRTWithAttributeReturnsUnretained {
59+
static FRTStruct* _Nonnull StaticMethodReturningFRT() __attribute__((swift_attr("returns_unretained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_copy() __attribute__((swift_attr("returns_unretained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_create() __attribute__((swift_attr("returns_unretained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_init() __attribute__((swift_attr("returns_unretained")));
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static FRTStruct* _Nonnull StaticMethodReturningFRT_clone() __attribute__((swift_attr("returns_unretained")));
64+
};
65+
66+
67+
// Global/free C++ functions returning FRT with both attributes swift_attr("returns_unretained") and swift_attr("returns_retained")
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FRTStruct* _Nonnull global_function_returning_FRT_with_both_attrs_returns_retained_returns_unretained() __attribute__((swift_attr("returns_retained"))) __attribute__((swift_attr("returns_unretained")));
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70+
// Struct having static method returning FRT with both attributes swift_attr("returns_unretained") and swift_attr("returns_retained")
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struct StructWithStaticMethodsReturningFRTWithBothAttributesReturnsRetainedAndReturnsUnretained {
72+
static FRTStruct* _Nonnull StaticMethodReturningFRT() __attribute__((swift_attr("returns_retained"))) __attribute__((swift_attr("returns_unretained")));
73+
};
74+
75+
struct NonFRTStruct {
76+
};
77+
78+
// Global/free C++ functions returning non-FRT
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NonFRTStruct* _Nonnull global_function_returning_non_FRT();
80+
NonFRTStruct* _Nonnull global_function_returning_non_FRT_with_attr_returns_retained() __attribute__((swift_attr("returns_retained")));
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NonFRTStruct* _Nonnull global_function_returning_non_FRT_with_attr_returns_unretained() __attribute__((swift_attr("returns_unretained")));
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NonFRTStruct* _Nonnull global_function_returning_non_FRT_create();
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NonFRTStruct* _Nonnull global_function_returning_non_FRT_copy();
84+
85+
86+
// Struct having static method returning non-FRT
87+
struct StructWithStaticMethodsReturningNonFRT {
88+
static NonFRTStruct* _Nonnull StaticMethodReturningNonFRT();
89+
static NonFRTStruct* _Nonnull StaticMethodReturningNonFRTWithAttrReturnsRetained() __attribute__((swift_attr("returns_retained")));
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static NonFRTStruct* _Nonnull StaticMethodReturningNonFRTWithAttrReturnsUnretained() __attribute__((swift_attr("returns_unretained")));
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static NonFRTStruct* _Nonnull StaticMethodReturningNonFRT_create();
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static NonFRTStruct* _Nonnull StaticMethodReturningNonFRT_copy();
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};
94+

‎test/Interop/Cxx/foreign-reference/Inputs/module.modulemap

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Original file line numberDiff line numberDiff line change
@@ -49,3 +49,7 @@ module DerivedFieldGetterReturnsOwnedFRT {
4949
requires cplusplus
5050
}
5151

52+
module FunctionsAndMethodsReturningFRT {
53+
header "cxx-functions-and-methods-returning-frt.h"
54+
requires cplusplus
55+
}

‎test/Interop/Cxx/foreign-reference/frt-retained-unretained-attributes-error.swift

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@@ -0,0 +1,10 @@
1+
// RUN: rm -rf %t
2+
// RUN: not %target-swift-frontend -typecheck -I %S/Inputs %s -cxx-interoperability-mode=upcoming-swift 2>&1 | %FileCheck %s
3+
4+
import FunctionsAndMethodsReturningFRT
5+
6+
// Testing diagnostic for Global/free C++ functions returning FRT returning FRT with both attributes swift_attr("returns_unretained") and swift_attr("returns_retained")
7+
let frtLocalVar1 = global_function_returning_FRT_with_both_attrs_returns_retained_returns_unretained(); // CHECK: error: 'global_function_returning_FRT_with_both_attrs_returns_retained_returns_unretained' cannot be annotated with both swift_attr('returns_retained') and swift_attr('returns_unretained') attributes
8+
9+
// Testing diagnostic for C++ Struct having static methods returning FRT returning FRT with both attributes swift_attr("returns_unretained") and swift_attr("returns_retained")
10+
let frtLocalVar2 = StructWithStaticMethodsReturningFRTWithBothAttributesReturnsRetainedAndReturnsUnretained.StaticMethodReturningFRT();; // CHECK: error: 'StaticMethodReturningFRT' cannot be annotated with both swift_attr('returns_retained') and swift_attr('returns_unretained') attributes

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