Sema: add support for `__attribute__((__swift_bridged_typedef__))`

[compnerd]

Summary

Extend the semantic attributes that clang processes for Swift to include
swift_bridged_typedef. This attribute enables typedefs to be bridged
into Swift with a bridged name.

This is based on the work of the original changes in
https://github.com/llvm/llvm-project-staging/commit/8afaf3aad2af43cfedca7a24cd817848c4e95c0c

[aaron.ballman]

clang/include/clang/Basic/Attr.td

2133

Should this be inherited on redeclarations?

2135

Does the default diagnostic text generate something bad that caused you to add typedefs here?

clang/include/clang/Basic/AttrDocs.td

3484

I think it would be helpful to show the String vs NSString behavior in a short code example of how to use the attribute.

clang/lib/Sema/SemaDeclAttr.cpp

7537

Should there be any type checking that the underlying type of the typedef is a sensible one to bridge?

clang/test/SemaObjC/attr-swift_bridged_typedef.m

9

Please also add some examples where the attribute has arguments. Also, should this work in Objective-C++ when using a using type alias? If so, an example showing that working would also be helpful.

[compnerd]

clang/include/clang/Basic/Attr.td

2133

I don't see why not. @rjmccall, @doug.gregor any reason to not permit this to be inherited by redeclarations?

2135

I don't remember, I'll double check.

clang/lib/Sema/SemaDeclAttr.cpp

7537

I can't really think of anything that you could check that would be valuable. What types of things were you thinking?

clang/test/SemaObjC/attr-swift_bridged_typedef.m

9

I don't know about the ObjC++11 case with the using. @doug.gregor or @rjmccall?

[compnerd]

Address feedback

[aaron.ballman]

clang/include/clang/Basic/Attr.td

2135

I noticed on a few other reviews that there was a field there, I wonder if the code originated before we added smarter logic for arbitrary subject lists.

clang/lib/Sema/SemaDeclAttr.cpp

7537

I was mostly thinking about builtin types like int, but I don't insist.

[compnerd]

clang/include/clang/Basic/Attr.td

2135

Yes, this code is definitely old. If there are sites that you notice that could be changed to something new, Im happy to work though those changes.

[compnerd]

clang/lib/Sema/SemaDeclAttr.cpp

7537

Typedefing int to something else and importing that with a different name is reasonable I believe. I'll add a test case.

[aaron.ballman]

clang/lib/Sema/SemaDeclAttr.cpp

7537

Okay, perfect, thank you for verifying!

[compnerd]

Add additional test case

[compnerd]

• Add additional test case that was requested

[compnerd]

clang/include/clang/Basic/Attr.td

2133

Checked, this should be inheritable, added a test case too.

[compnerd]

• make the attribute inheritable
• add a test case for inheritance
• add a test case for C++ type alias

[aaron.ballman]

LGTM with some test location nits.

clang/test/SemaObjC/attr-swift_bridged_typedef.m

3

Can you split this bit off into a separate test in the AST directory? Then you don't have to contend with the errors in the test file and it's a more realistic test (AST tests with errors present always leave me wondering how the AST will change as we add error recovery functionality to the AST).

clang/test/SemaObjC/attr-swift_bridged_typedef.mm

1 ↗

(On Diff #291687)

Can you move this test to the AST directory as well?

clang/include/clang/Basic/Attr.td

 def Regparm : TypeAttr {
   let Spellings = [GCC<"regparm">];
   let Args = [UnsignedArgument<"NumParams">];
   let Documentation = [RegparmDocs];
   // Represented as part of the enclosing function type.
   let ASTNode = 0;
 }
 
+def SwiftBridgedTypedef : InheritableAttr {
+  let Spellings = [GNU<"swift_bridged_typedef">];
+  let Subjects = SubjectList<[TypedefName], ErrorDiag>;
+  let Documentation = [SwiftBridgedTypedefDocs];
+}
+
 def SwiftObjCMembers : Attr {
   let Spellings = [GNU<"swift_objc_members">];
   let Subjects = SubjectList<[ObjCInterface], ErrorDiag>;
   let Documentation = [SwiftObjCMembersDocs];
 }
 
 def SwiftError : InheritableAttr {
   let Spellings = [GNU<"swift_error">];

clang/include/clang/Basic/AttrDocs.td

 
 def SwiftDocs : DocumentationCategory<"Customizing Swift Import"> {
   let Content = [{
 Clang supports additional attributes for customizing how APIs are imported into
 Swift.
   }];
 }
 
+def SwiftBridgedTypedefDocs : Documentation {
+  let Category = SwiftDocs;
+  let Heading = "swift_bridged";
+  let Content = [{
+The ``swift_bridged_typedef`` attribute indicates that when the typedef to which
+the attribute appertains is imported into Swift, it should refer to the bridged
+Swift type (e.g. Swift's ``String``) rather than the Objective-C type as written
+(e.g. ``NSString``).
+
+  .. code-block:: c
+
+    @interface NSString;
+    typedef NSString *AliasedString __attribute__((__swift_bridged_typedef__));
+
+    extern void acceptsAliasedString(AliasedString _Nonnull parameter);
+
+In this case, the function ``acceptsAliasedString`` will be imported into Swift
+as a function which accepts a ``String`` type parameter.
+  }];
+}
+
 def SwiftObjCMembersDocs : Documentation {
   let Category = SwiftDocs;
   let Heading = "swift_objc_members";
   let Content = [{
 This attribute indicates that Swift subclasses and members of Swift extensions
 of this class will be implicitly marked with the ``@objcMembers`` Swift
 attribute, exposing them back to Objective-C.
   }];

clang/lib/Sema/SemaDeclAttr.cpp

static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_ArgumentWithTypeTag:
     handleArgumentWithTypeTagAttr(S, D, AL);
     break;
   case ParsedAttr::AT_TypeTagForDatatype:
     handleTypeTagForDatatypeAttr(S, D, AL);
     break;
 
   // Swift attributes.
+  case ParsedAttr::AT_SwiftBridgedTypedef:
+    handleSimpleAttribute<SwiftBridgedTypedefAttr>(S, D, AL);
+    break;
   case ParsedAttr::AT_SwiftError:
     handleSwiftError(S, D, AL);
     break;
   case ParsedAttr::AT_SwiftObjCMembers:
     handleSimpleAttribute<SwiftObjCMembersAttr>(S, D, AL);
     break;
 
   // XRay attributes.

clang/test/AST/attr-swift_bridged_typedef.m

+// RUN: %clang_cc1 -fsyntax-only -ast-dump %s | FileCheck %s
+
+typedef struct T TBridged __attribute((__swift_bridged_typedef__));
+// CHECK: TypedefDecl {{.*}} TBridged 'struct T'
+// CHECK: SwiftBridgedTypedefAttr
+
+typedef struct T TBridged;
+// CHECK: TypedefDecl {{.*}} TBridged 'struct T'
+// CHECK: SwiftBridgedTypedefAttr

clang/test/AST/attr-swift_bridged_typedef.mm

+// RUN: %clang_cc1 -fsyntax-only %s -ast-dump | FileCheck %s
+
+@interface NSString
+@end
+
+using NSStringAlias __attribute__((__swift_bridged_typedef__)) = NSString *;
+// CHECK: TypeAliasDecl {{.*}} NSStringAlias 'NSString *'
+// CHECK: SwiftBridgedTypedefAttr

clang/test/Misc/pragma-attribute-supported-attributes-list.test

 // CHECK-NEXT: Restrict (SubjectMatchRule_function)
 // CHECK-NEXT: ReturnTypestate (SubjectMatchRule_function, SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: ReturnsNonNull (SubjectMatchRule_objc_method, SubjectMatchRule_function)
 // CHECK-NEXT: ReturnsTwice (SubjectMatchRule_function)
 // CHECK-NEXT: ScopedLockable (SubjectMatchRule_record)
 // CHECK-NEXT: Section (SubjectMatchRule_function, SubjectMatchRule_variable_is_global, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property)
 // CHECK-NEXT: SetTypestate (SubjectMatchRule_function_is_member)
 // CHECK-NEXT: SpeculativeLoadHardening (SubjectMatchRule_function, SubjectMatchRule_objc_method)
+// CHECK-NEXT: SwiftBridgedTypedef (SubjectMatchRule_type_alias)
 // CHECK-NEXT: SwiftContext (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftError (SubjectMatchRule_function, SubjectMatchRule_objc_method)
 // CHECK-NEXT: SwiftErrorResult (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftIndirectResult (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftObjCMembers (SubjectMatchRule_objc_interface)
 // CHECK-NEXT: TLSModel (SubjectMatchRule_variable_is_thread_local)
 // CHECK-NEXT: Target (SubjectMatchRule_function)
 // CHECK-NEXT: TestTypestate (SubjectMatchRule_function_is_member)

clang/test/SemaObjC/attr-swift_bridged_typedef.m

+// RUN: %clang_cc1 -verify -fsyntax-only %s
+
+@interface NSString
+@end
+
+typedef NSString *NSStringAlias __attribute__((__swift_bridged_typedef__));
+
+typedef int IntAlias __attribute__((__swift_bridged_typedef__));
+
+struct __attribute__((swift_bridged_typedef)) S {};
+// expected-error@-1 {{'swift_bridged_typedef' attribute only applies to typedefs}}
+
+typedef unsigned char UnsignedChar __attribute__((__swift_bridged_typedef__("UnsignedChar")));
+// expected-error@-1 {{'__swift_bridged_typedef__' attribute takes no arguments}}