Author: fahadnayyar
Date: 2025-05-07T13:42:39-07:00
New Revision: 62a2f0fdc74f086c875833eefe9099bd30f41957

URL: 
https://github.com/llvm/llvm-project/commit/62a2f0fdc74f086c875833eefe9099bd30f41957
DIFF: 
https://github.com/llvm/llvm-project/commit/62a2f0fdc74f086c875833eefe9099bd30f41957.diff

LOG: [APINotes] Add support for SWIFT_RETURED_AS_UNRETAINED_BY_DEFAULT (#138699)

This patch adds support in APINotes for annotating C++ user-defined
types with: `swift_attr("returned_as_unretained_by_default")`
This attribute allows to specify a default ownership convention for
return values of `SWIFT_SHARED_REFERENCE` c++ types. Specifically, it
marks all unannotated return values of this type as `unretained` (`+0`)
by default, unless explicitly overridden at the API level using
`swift_attr("returns_retained")` or `swift_attr("returns_unretained")`.

The corresponding Swift compiler support for this annotation enables
developers to suppress warnings about unannotated return ownership in
large codebases while maintaining safe and predictable ownership
semantics. By enabling this in APINotes, library authors can define this
behavior externally without needing to modify C++ source headers
directly.

### Example usage in APINotes:
```
- Name: RefCountedTypeWithDefaultConvention
  SwiftImportAs: reference
  SwiftDefaultOwnership: unretained

```
rdar://150764491

Added: 
    

Modified: 
    clang/include/clang/APINotes/Types.h
    clang/lib/APINotes/APINotesFormat.h
    clang/lib/APINotes/APINotesReader.cpp
    clang/lib/APINotes/APINotesWriter.cpp
    clang/lib/APINotes/APINotesYAMLCompiler.cpp
    clang/lib/Sema/SemaAPINotes.cpp
    clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes
    clang/test/APINotes/Inputs/Headers/SwiftImportAs.h
    clang/test/APINotes/swift-import-as.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/APINotes/Types.h 
b/clang/include/clang/APINotes/Types.h
index 9c01978fd49ef..0f2e49613b514 100644
--- a/clang/include/clang/APINotes/Types.h
+++ b/clang/include/clang/APINotes/Types.h
@@ -737,6 +737,7 @@ class TagInfo : public CommonTypeInfo {
   std::optional<std::string> SwiftImportAs;
   std::optional<std::string> SwiftRetainOp;
   std::optional<std::string> SwiftReleaseOp;
+  std::optional<std::string> SwiftDefaultOwnership;
 
   /// The Swift protocol that this type should be automatically conformed to.
   std::optional<std::string> SwiftConformance;
@@ -786,6 +787,8 @@ class TagInfo : public CommonTypeInfo {
       SwiftRetainOp = RHS.SwiftRetainOp;
     if (!SwiftReleaseOp)
       SwiftReleaseOp = RHS.SwiftReleaseOp;
+    if (!SwiftDefaultOwnership)
+      SwiftDefaultOwnership = RHS.SwiftDefaultOwnership;
 
     if (!SwiftConformance)
       SwiftConformance = RHS.SwiftConformance;
@@ -815,6 +818,7 @@ inline bool operator==(const TagInfo &LHS, const TagInfo 
&RHS) {
          LHS.SwiftImportAs == RHS.SwiftImportAs &&
          LHS.SwiftRetainOp == RHS.SwiftRetainOp &&
          LHS.SwiftReleaseOp == RHS.SwiftReleaseOp &&
+         LHS.SwiftDefaultOwnership == RHS.SwiftDefaultOwnership &&
          LHS.SwiftConformance == RHS.SwiftConformance &&
          LHS.isFlagEnum() == RHS.isFlagEnum() &&
          LHS.isSwiftCopyable() == RHS.isSwiftCopyable() &&

diff  --git a/clang/lib/APINotes/APINotesFormat.h 
b/clang/lib/APINotes/APINotesFormat.h
index 939235179c363..bb0c276e74964 100644
--- a/clang/lib/APINotes/APINotesFormat.h
+++ b/clang/lib/APINotes/APINotesFormat.h
@@ -24,7 +24,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// API notes file minor version number.
 ///
 /// When the format changes IN ANY WAY, this number should be incremented.
-const uint16_t VERSION_MINOR = 34; // SwiftReturnOwnership
+const uint16_t VERSION_MINOR = 35; // SwiftDefaultOwnership
 
 const uint8_t kSwiftConforms = 1;
 const uint8_t kSwiftDoesNotConform = 2;

diff  --git a/clang/lib/APINotes/APINotesReader.cpp 
b/clang/lib/APINotes/APINotesReader.cpp
index 646eabd2a5ecd..2ba30ca427ae4 100644
--- a/clang/lib/APINotes/APINotesReader.cpp
+++ b/clang/lib/APINotes/APINotesReader.cpp
@@ -624,6 +624,13 @@ class TagTableInfo
                                         ReleaseOpLength - 1);
       Data += ReleaseOpLength - 1;
     }
+    unsigned DefaultOwnershipLength =
+        endian::readNext<uint16_t, llvm::endianness::little>(Data);
+    if (DefaultOwnershipLength > 0) {
+      Info.SwiftDefaultOwnership = std::string(
+          reinterpret_cast<const char *>(Data), DefaultOwnershipLength - 1);
+      Data += DefaultOwnershipLength - 1;
+    }
     if (unsigned ConformanceLength =
             endian::readNext<uint16_t, llvm::endianness::little>(Data)) {
       Info.SwiftConformance = std::string(reinterpret_cast<const char *>(Data),

diff  --git a/clang/lib/APINotes/APINotesWriter.cpp 
b/clang/lib/APINotes/APINotesWriter.cpp
index 1aae07bbdd30e..7578bc37b5c68 100644
--- a/clang/lib/APINotes/APINotesWriter.cpp
+++ b/clang/lib/APINotes/APINotesWriter.cpp
@@ -1274,6 +1274,7 @@ class TagTableInfo : public 
CommonTypeTableInfo<TagTableInfo, TagInfo> {
     return 2 + (TI.SwiftImportAs ? TI.SwiftImportAs->size() : 0) +
            2 + (TI.SwiftRetainOp ? TI.SwiftRetainOp->size() : 0) +
            2 + (TI.SwiftReleaseOp ? TI.SwiftReleaseOp->size() : 0) +
+           2 + (TI.SwiftDefaultOwnership ? TI.SwiftDefaultOwnership->size() : 
0) +
            2 + (TI.SwiftConformance ? TI.SwiftConformance->size() : 0) +
            3 + getCommonTypeInfoSize(TI);
     // clang-format on
@@ -1322,6 +1323,12 @@ class TagTableInfo : public 
CommonTypeTableInfo<TagTableInfo, TagInfo> {
     } else {
       writer.write<uint16_t>(0);
     }
+    if (auto DefaultOwnership = TI.SwiftDefaultOwnership) {
+      writer.write<uint16_t>(DefaultOwnership->size() + 1);
+      OS.write(DefaultOwnership->c_str(), DefaultOwnership->size());
+    } else {
+      writer.write<uint16_t>(0);
+    }
     if (auto Conformance = TI.SwiftConformance) {
       writer.write<uint16_t>(Conformance->size() + 1);
       OS.write(Conformance->c_str(), Conformance->size());

diff  --git a/clang/lib/APINotes/APINotesYAMLCompiler.cpp 
b/clang/lib/APINotes/APINotesYAMLCompiler.cpp
index 414a59a4f12d0..803410c54c646 100644
--- a/clang/lib/APINotes/APINotesYAMLCompiler.cpp
+++ b/clang/lib/APINotes/APINotesYAMLCompiler.cpp
@@ -460,6 +460,7 @@ struct Tag {
   std::optional<std::string> SwiftImportAs;
   std::optional<std::string> SwiftRetainOp;
   std::optional<std::string> SwiftReleaseOp;
+  std::optional<std::string> SwiftDefaultOwnership;
   std::optional<std::string> SwiftConformance;
   std::optional<EnumExtensibilityKind> EnumExtensibility;
   std::optional<bool> FlagEnum;
@@ -500,6 +501,7 @@ template <> struct MappingTraits<Tag> {
     IO.mapOptional("SwiftImportAs", T.SwiftImportAs);
     IO.mapOptional("SwiftReleaseOp", T.SwiftReleaseOp);
     IO.mapOptional("SwiftRetainOp", T.SwiftRetainOp);
+    IO.mapOptional("SwiftDefaultOwnership", T.SwiftDefaultOwnership);
     IO.mapOptional("SwiftConformsTo", T.SwiftConformance);
     IO.mapOptional("EnumExtensibility", T.EnumExtensibility);
     IO.mapOptional("FlagEnum", T.FlagEnum);
@@ -990,6 +992,8 @@ class YAMLConverter {
       TI.SwiftReleaseOp = T.SwiftReleaseOp;
     if (T.SwiftConformance)
       TI.SwiftConformance = T.SwiftConformance;
+    if (T.SwiftDefaultOwnership)
+      TI.SwiftDefaultOwnership = T.SwiftDefaultOwnership;
 
     if (T.SwiftCopyable)
       TI.setSwiftCopyable(T.SwiftCopyable);

diff  --git a/clang/lib/Sema/SemaAPINotes.cpp b/clang/lib/Sema/SemaAPINotes.cpp
index b354bb7b06435..def909fc2478d 100644
--- a/clang/lib/Sema/SemaAPINotes.cpp
+++ b/clang/lib/Sema/SemaAPINotes.cpp
@@ -643,6 +643,9 @@ static void ProcessAPINotes(Sema &S, TagDecl *D, const 
api_notes::TagInfo &Info,
   if (auto ReleaseOp = Info.SwiftReleaseOp)
     D->addAttr(
         SwiftAttrAttr::Create(S.Context, "release:" + ReleaseOp.value()));
+  if (auto DefaultOwnership = Info.SwiftDefaultOwnership)
+    D->addAttr(SwiftAttrAttr::Create(
+        S.Context, "returned_as_" + DefaultOwnership.value() + "_by_default"));
 
   if (auto ConformsTo = Info.SwiftConformance)
     D->addAttr(

diff  --git a/clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes 
b/clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes
index 88e0da1382d6c..66fc46e50ba0d 100644
--- a/clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes
+++ b/clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes
@@ -14,6 +14,11 @@ Tags:
   SwiftReleaseOp: RCRelease
   SwiftRetainOp: RCRetain
   SwiftConformsTo: MySwiftModule.MySwiftRefCountedProtocol
+- Name: RefCountedTypeWithDefaultConvention
+  SwiftImportAs: reference
+  SwiftReleaseOp: release
+  SwiftRetainOp: retain
+  SwiftDefaultOwnership: unretained
 - Name: NonCopyableType
   SwiftCopyable: false
   SwiftConformsTo: MySwiftModule.MySwiftNonCopyableProtocol

diff  --git a/clang/test/APINotes/Inputs/Headers/SwiftImportAs.h 
b/clang/test/APINotes/Inputs/Headers/SwiftImportAs.h
index b6900fee8a979..20b8f04b4a914 100644
--- a/clang/test/APINotes/Inputs/Headers/SwiftImportAs.h
+++ b/clang/test/APINotes/Inputs/Headers/SwiftImportAs.h
@@ -19,3 +19,7 @@ struct CopyableType { int value; };
 
 struct NonEscapableType { int value; };
 struct EscapableType { int value; };
+
+struct RefCountedTypeWithDefaultConvention {};
+inline void retain(RefCountedType *x) {}
+inline void release(RefCountedType *x) {}

diff  --git a/clang/test/APINotes/swift-import-as.cpp 
b/clang/test/APINotes/swift-import-as.cpp
index 3981ef1ed419a..929f924f2afee 100644
--- a/clang/test/APINotes/swift-import-as.cpp
+++ b/clang/test/APINotes/swift-import-as.cpp
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps 
-fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules 
-fsyntax-only -I %S/Inputs/Headers %s -x c++
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps 
-fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules 
-I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter ImmortalRefType | 
FileCheck -check-prefix=CHECK-IMMORTAL %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps 
-fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules 
-I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter RefCountedType | 
FileCheck -check-prefix=CHECK-REF-COUNTED %s
+// RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps 
-fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules 
-I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter 
RefCountedTypeWithDefaultConvention | FileCheck 
-check-prefix=CHECK-REF-COUNTED-DEFAULT %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps 
-fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules 
-I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter NonCopyableType | 
FileCheck -check-prefix=CHECK-NON-COPYABLE %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps 
-fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules 
-I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter CopyableType | 
FileCheck -check-prefix=CHECK-COPYABLE %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps 
-fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules 
-I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter NonEscapableType | 
FileCheck -check-prefix=CHECK-NON-ESCAPABLE %s
@@ -26,6 +27,13 @@
 // CHECK-REF-COUNTED: SwiftAttrAttr {{.+}} <<invalid sloc>> "release:RCRelease"
 // CHECK-REF-COUNTED: SwiftAttrAttr {{.+}} <<invalid sloc>> 
"conforms_to:MySwiftModule.MySwiftRefCountedProtocol"
 
+// CHECK-REF-COUNTED-DEFAULT: Dumping RefCountedTypeWithDefaultConvention:
+// CHECK-REF-COUNTED-DEFAULT-NEXT: CXXRecordDecl {{.+}} imported in 
SwiftImportAs {{.+}} struct RefCountedTypeWithDefaultConvention
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> 
"import_reference"
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> 
"retain:retain"
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> 
"release:release"
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> 
"returned_as_unretained_by_default"
+
 // CHECK-NON-COPYABLE: Dumping NonCopyableType:
 // CHECK-NON-COPYABLE-NEXT: CXXRecordDecl {{.+}} imported in SwiftImportAs 
{{.+}} struct NonCopyableType
 // CHECK-NON-COPYABLE: SwiftAttrAttr {{.+}} <<invalid sloc>> 
"conforms_to:MySwiftModule.MySwiftNonCopyableProtocol"


        
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