PrintAsClang: Print @cdecl enums in the compatibility header

xymus · xymus · commit 138e2daa3ec7 · 2025-06-09T11:54:13.000-07:00
Print @cdecl enums in the C section of the compatibility header. Use and extend the macros to support C compiler clients. The macro is adapted to the features supported by the client compiler. It uses an Objective-C style macro with raw type when available and fallbacks to a simple typedef for C compatibility.
diff --git a/include/swift/PrintAsClang/ClangMacros.def b/include/swift/PrintAsClang/ClangMacros.def
@@ -176,20 +176,37 @@ CLANG_MACRO_CONDITIONAL("SWIFT_ENUM_ATTR", "(_extensibility)", \
                         "__attribute__((enum_extensibility(_extensibility)))")
 
 CLANG_MACRO_BODY("SWIFT_ENUM", \
-    "# define SWIFT_ENUM(_type, _name, _extensibility) " \
+    "# if (defined(__cplusplus) && __cplusplus >= 201103L) || " \
+    "     (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L) || " \
+    "     __has_feature(objc_fixed_enum)\n" \
+    "#  define SWIFT_ENUM(_type, _name, _extensibility) " \
         "enum _name : _type _name; " \
         "enum SWIFT_ENUM_ATTR(_extensibility) SWIFT_ENUM_EXTRA _name : _type\n" \
-    "# if __has_feature(generalized_swift_name)\n" \
-    "#  define SWIFT_ENUM_NAMED(_type, _name, SWIFT_NAME, _extensibility) " \
-        "enum _name : _type _name SWIFT_COMPILE_NAME(SWIFT_NAME); " \
-        "enum SWIFT_COMPILE_NAME(SWIFT_NAME) SWIFT_ENUM_ATTR(_extensibility) " \
-            "SWIFT_ENUM_EXTRA _name : _type\n" \
+    "#  if __has_feature(generalized_swift_name)\n" \
+    "#   define SWIFT_ENUM_NAMED(_type, _name, SWIFT_NAME, _extensibility) " \
+         "enum _name : _type _name SWIFT_COMPILE_NAME(SWIFT_NAME); " \
+         "enum SWIFT_COMPILE_NAME(SWIFT_NAME) SWIFT_ENUM_ATTR(_extensibility) " \
+             "SWIFT_ENUM_EXTRA _name : _type\n" \
+    "#  else\n" \
+    "#   define SWIFT_ENUM_NAMED(_type, _name, SWIFT_NAME, _extensibility) " \
+         "SWIFT_ENUM(_type, _name, _extensibility)\n" \
+    "#  endif\n" \
     "# else\n" \
+    "#  define SWIFT_ENUM(_type, _name, _extensibility) _type _name; enum \n" \
     "#  define SWIFT_ENUM_NAMED(_type, _name, SWIFT_NAME, _extensibility) " \
         "SWIFT_ENUM(_type, _name, _extensibility)\n" \
     "# endif")
 CLANG_MACRO_DEFINED("SWIFT_ENUM_NAMED")
 
+CLANG_MACRO_BODY("SWIFT_ENUM_TAG", \
+    "# if (defined(__cplusplus) && __cplusplus >= 201103L) || " \
+    "     (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L) || " \
+    "     __has_feature(objc_fixed_enum)\n" \
+    "#  define SWIFT_ENUM_TAG enum\n" \
+    "# else\n" \
+    "#  define SWIFT_ENUM_TAG\n" \
+    "# endif")
+
 CLANG_MACRO("SWIFT_UNAVAILABLE", , "__attribute__((unavailable))")
 CLANG_MACRO("SWIFT_UNAVAILABLE_MSG", "(msg)", "__attribute__((unavailable(msg)))")
 
diff --git a/lib/PrintAsClang/DeclAndTypePrinter.cpp b/lib/PrintAsClang/DeclAndTypePrinter.cpp
@@ -2385,8 +2385,14 @@ class DeclAndTypePrinter::Implementation
   }
 
   void maybePrintTagKeyword(const TypeDecl *NTD) {
-    if (isa<EnumDecl>(NTD) && !NTD->hasClangNode()) {
-      os << "enum ";
+    if (auto *ED = dyn_cast<EnumDecl>(NTD); !NTD->hasClangNode()) {
+      if (ED->getAttrs().hasAttribute<CDeclAttr>()) {
+        // We should be able to use the tag macro for all printed enums but
+        // for now restrict it to @cdecl to guard it behind the feature flag.
+        os << "SWIFT_ENUM_TAG ";
+      } else {
+        os << "enum ";
+      }
       return;
     }
 
@@ -3016,9 +3022,17 @@ bool DeclAndTypePrinter::shouldInclude(const ValueDecl *VD) {
        (outputLang == OutputLanguageMode::C))
     return false;
 
-  // C output mode only accepts @cdecl functions.
+  // C output mode only prints @cdecl functions and enums.
   if (outputLang == OutputLanguageMode::C &&
-      !cdeclKind) {
+      !cdeclKind && !isa<EnumDecl>(VD)) {
+    return false;
+  }
+
+  // The C mode prints @cdecl enums and reject other enums,
+  // while other modes accept other enums and reject @cdecl ones.
+  if (isa<EnumDecl>(VD) &&
+      VD->getAttrs().hasAttribute<CDeclAttr>() !=
+        (outputLang == OutputLanguageMode::C)) {
     return false;
   }
 
diff --git a/lib/PrintAsClang/ModuleContentsWriter.cpp b/lib/PrintAsClang/ModuleContentsWriter.cpp
@@ -530,6 +530,10 @@ class ModuleWriter {
   }
 
   void forwardDeclare(const EnumDecl *ED) {
+    // Don't forward declare C enums.
+    if (ED->getAttrs().getAttribute<CDeclAttr>())
+      return;
+
     assert(ED->isObjC() || ED->hasClangNode());
     
     forwardDeclare(ED, [&]{
@@ -864,7 +868,7 @@ class ModuleWriter {
 
     SmallVector<ProtocolConformance *, 1> conformances;
     auto errorTypeProto = ctx.getProtocol(KnownProtocolKind::Error);
-    if (outputLangMode != OutputLanguageMode::Cxx
+    if (outputLangMode == OutputLanguageMode::ObjC
         && ED->lookupConformance(errorTypeProto, conformances)) {
       bool hasDomainCase = std::any_of(ED->getAllElements().begin(),
                                        ED->getAllElements().end(),
diff --git a/test/PrintAsObjC/cdecl-enums.swift b/test/PrintAsObjC/cdecl-enums.swift
@@ -0,0 +1,126 @@
+/// Variant of PrintAsObjC/enums.swift for @cdecl enums.
+
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-source-import \
+// RUN:   -emit-module -emit-module-doc -o %t %s \
+// RUN:   -import-objc-header %S/Inputs/enums.h \
+// RUN:   -emit-objc-header-path %t/enums.h \
+// RUN:   -disable-objc-attr-requires-foundation-module \
+// RUN:   -enable-experimental-feature CDecl
+
+// RUN: %FileCheck %s --input-file %t/enums.h
+// RUN: %FileCheck -check-prefix=NEGATIVE %s --input-file %t/enums.h
+// RUN: %check-in-clang %t/enums.h
+
+// REQUIRES: swift_feature_CDecl
+// REQUIRES: objc_interop
+
+import Foundation
+
+// NEGATIVE-NOT: enum EnumNamed
+
+/// No error domains in C mode.
+// NEGATIVE-NOT: @"main.
+
+// CHECK-LABEL: typedef SWIFT_ENUM_NAMED(ptrdiff_t, ObjcEnumNamed, "EnumNamed", closed) {
+// CHECK-NEXT:   ObjcEnumNamedA = 0,
+// CHECK-NEXT:   ObjcEnumNamedB = 1,
+// CHECK-NEXT:   ObjcEnumNamedC = 2,
+// CHECK-NEXT:   ObjcEnumNamedD = 3,
+// CHECK-NEXT:   ObjcEnumNamedHelloDolly = 4,
+// CHECK-NEXT: };
+
+@cdecl("ObjcEnumNamed") enum EnumNamed: Int {
+  case A, B, C, d, helloDolly
+}
+
+// CHECK-LABEL: typedef SWIFT_ENUM_NAMED(unsigned int, ExplicitValues, "ExplicitValues", closed) {
+// CHECK-NEXT:   ExplicitValuesZim = 0,
+// CHECK-NEXT:   ExplicitValuesZang = 219,
+// CHECK-NEXT:   ExplicitValuesZung = 220,
+// CHECK-NEXT: };
+// NEGATIVE-NOT: ExplicitValuesDomain
+
+@cdecl("ExplicitValues") enum ExplicitValues: CUnsignedInt {
+  case Zim, Zang = 219, Zung
+
+  func methodNotExportedToC() {}
+}
+
+// CHECK: /// Foo: A feer, a female feer.
+// CHECK-NEXT: typedef SWIFT_ENUM_NAMED(int, FooComments, "FooComments", closed) {
+// CHECK: /// Zim: A zeer, a female zeer.
+// CHECK-NEXT:   FooCommentsZim = 0,
+// CHECK-NEXT:   FooCommentsZang = 1,
+// CHECK-NEXT:   FooCommentsZung = 2,
+// CHECK-NEXT: }
+
+/// Foo: A feer, a female feer.
+@cdecl("FooComments") public enum FooComments: CInt {
+  /// Zim: A zeer, a female zeer.
+  case Zim
+  case Zang, Zung
+}
+
+// CHECK-LABEL: typedef SWIFT_ENUM_NAMED(int16_t, NegativeValues, "NegativeValues", closed) {
+// CHECK-NEXT:   Zang = -219,
+// CHECK-NEXT:   Zung = -218,
+// CHECK-NEXT: };
+@cdecl("NegativeValues") enum NegativeValues: Int16 {
+  case Zang = -219, Zung
+
+  func methodNotExportedToC() {}
+}
+
+// CHECK-LABEL: typedef SWIFT_ENUM_NAMED(ptrdiff_t, SomeError, "SomeError", closed) {
+// CHECK-NEXT:   SomeErrorBadness = 9001,
+// CHECK-NEXT:   SomeErrorWorseness = 9002,
+// CHECK-NEXT: };
+@cdecl("SomeError") enum SomeError: Int, Error {
+  case Badness = 9001
+  case Worseness
+}
+
+// CHECK-LABEL: typedef SWIFT_ENUM_NAMED(ptrdiff_t, SomeOtherError, "SomeOtherError", closed) {
+// CHECK-NEXT:   SomeOtherErrorDomain = 0,
+// CHECK-NEXT: };
+@cdecl("SomeOtherError") enum SomeOtherError: Int, Error {
+  case Domain
+}
+
+// CHECK-LABEL: typedef SWIFT_ENUM_NAMED(ptrdiff_t, ObjcErrorType, "SomeRenamedErrorType", closed) {
+// CHECK-NEXT:   ObjcErrorTypeBadStuff = 0,
+// CHECK-NEXT: };
+@cdecl("ObjcErrorType") enum SomeRenamedErrorType: Int, Error {
+  case BadStuff
+}
+
+@cdecl("acceptMemberImported") func acceptMemberImported(a: Wrapper.Raw, b: Wrapper.Enum, c: Wrapper.Options, d: Wrapper.Typedef, e: Wrapper.Anon, ee: Wrapper.Anon2) {}
+// CHECK-LABEL: SWIFT_EXTERN void acceptMemberImported(enum MemberRaw a, enum MemberEnum b, MemberOptions c, enum MemberTypedef d, MemberAnon e, MemberAnon2 ee) SWIFT_NOEXCEPT;
+
+@cdecl("acceptPlainEnum") func acceptPlainEnum(_: NSMalformedEnumMissingTypedef) {}
+// CHECK-LABEL: SWIFT_EXTERN void acceptPlainEnum(enum NSMalformedEnumMissingTypedef) SWIFT_NOEXCEPT;
+
+@cdecl("acceptTopLevelImported") func acceptTopLevelImported(a: TopLevelRaw, b: TopLevelEnum, c: TopLevelOptions, d: TopLevelTypedef, e: TopLevelAnon) {}
+// CHECK-LABEL: SWIFT_EXTERN void acceptTopLevelImported(enum TopLevelRaw a, TopLevelEnum b, TopLevelOptions c, TopLevelTypedef d, TopLevelAnon e) SWIFT_NOEXCEPT;
+
+@cdecl("takeAndReturnEnumC") func takeAndReturnEnumC(_ foo: FooComments) -> NegativeValues {
+  return .Zung
+}
+// CHECK-LABEL: SWIFT_EXTERN SWIFT_ENUM_TAG NegativeValues takeAndReturnEnumC(SWIFT_ENUM_TAG FooComments foo) SWIFT_NOEXCEPT SWIFT_WARN_UNUSED_RESULT;
+
+@cdecl("takeAndReturnRenamedEnum") func takeAndReturnRenamedEnum(_ foo: EnumNamed) -> EnumNamed {
+  return .A
+}
+// CHECK-LABEL: SWIFT_EXTERN SWIFT_ENUM_TAG ObjcEnumNamed takeAndReturnRenamedEnum(SWIFT_ENUM_TAG ObjcEnumNamed foo) SWIFT_NOEXCEPT SWIFT_WARN_UNUSED_RESULT;
+
+/// Objective-C user.
+
+// CHECK-LABEL: SWIFT_ENUM_FWD_DECL(int, FooComments)
+// CHECK-LABEL: SWIFT_ENUM_FWD_DECL(int16_t, NegativeValues)
+
+// CHECK-LABEL: SWIFT_EXTERN SWIFT_ENUM_TAG NegativeValues takeAndReturnEnumObjC(SWIFT_ENUM_TAG FooComments foo) SWIFT_NOEXCEPT SWIFT_WARN_UNUSED_RESULT;
+@_cdecl("takeAndReturnEnumObjC") func takeAndReturnEnumObjC(_ foo: FooComments) -> NegativeValues {
+  return .Zung
+}
diff --git a/test/PrintAsObjC/cdecl-official.swift b/test/PrintAsObjC/cdecl-official.swift
@@ -27,6 +27,22 @@
 // CHECK: extern "C" {
 // CHECK: #endif
 
+// CHECK: /// Enums
+// CHECK: typedef SWIFT_ENUM_NAMED(int, CEnum, "CEnum", closed) {
+// CHECK:   CEnumA = 0,
+// CHECK:   CEnumB = 1,
+// CHECK: };
+
+// CHECK: typedef SWIFT_ENUM_NAMED(long, CEnumRenamed_CName, "CEnumRenamed", closed) {
+// CHECK:   CEnumRenamed_CNameA = 0,
+// CHECK:   CEnumRenamed_CNameB = 1,
+// CHECK: };
+
+// CHECK: typedef SWIFT_ENUM_NAMED(char, zCEnumDefinedLate, "zCEnumDefinedLate", closed) {
+// CHECK:   CEnumDefinedLateA = 0,
+// CHECK:   CEnumDefinedLateB = 1,
+// CHECK: };
+
 /// My documentation
 @cdecl("simple")
 func a_simple(x: Int, bar y: Int) -> Int { return x }
@@ -62,6 +78,30 @@ func g_nullablePointers(_ x: UnsafeMutableRawPointer,
                           z: UnsafeMutableRawPointer!) {}
 // CHECK: SWIFT_EXTERN void nullable_pointers(void * _Nonnull x, void * _Nullable y, void * _Null_unspecified z) SWIFT_NOEXCEPT;
 
+/// Enums
+
+@cdecl("CEnum")
+enum CEnum: CInt { case A, B }
+
+@cdecl("CEnumRenamed_CName")
+enum CEnumRenamed: CLong { case A, B }
+
+@cdecl("use_enum")
+func h_useCEnum(e: CEnum) -> CEnum { return e }
+// CHECK: SWIFT_EXTERN SWIFT_ENUM_TAG CEnum use_enum(SWIFT_ENUM_TAG CEnum e) SWIFT_NOEXCEPT SWIFT_WARN_UNUSED_RESULT;
+
+@cdecl("use_enum_renamed")
+func i_useCEnumLong(e: CEnumRenamed) -> CEnumRenamed { return e }
+// CHECK: SWIFT_EXTERN SWIFT_ENUM_TAG CEnumRenamed_CName use_enum_renamed(SWIFT_ENUM_TAG CEnumRenamed_CName e) SWIFT_NOEXCEPT SWIFT_WARN_UNUSED_RESULT;
+
+@cdecl("use_enum_late")
+func j_useCEnumChar(e: zCEnumDefinedLate) -> zCEnumDefinedLate { return e }
+// CHECK: SWIFT_EXTERN SWIFT_ENUM_TAG zCEnumDefinedLate use_enum_late(SWIFT_ENUM_TAG zCEnumDefinedLate e) SWIFT_NOEXCEPT SWIFT_WARN_UNUSED_RESULT;
+
+/// Declare this enum late in the source file and in alphabetical order.
+@cdecl("zCEnumDefinedLate")
+enum zCEnumDefinedLate: CChar { case A, B }
+
 // CHECK:      #if defined(__cplusplus)
 // CHECK-NEXT: }
 // CHECK-NEXT: #endif
@@ -74,5 +114,10 @@ int main() {
     ptrdiff_t x = simple(42, 43);
     primitiveTypes(1, 2, 3, 'a', 1.0f, 2.0, true);
     has_keyword_arg_names(1, 2);
+
+    (void)use_enum(CEnumA);
+    (void)use_enum_renamed(CEnumRenamed_CNameB);
+    (void)use_enum_late(zCEnumDefinedLateA);
+
     return_never();
 }
