Add a builtin to generate the ObjC @encode string for a type.

We need the encode string to be able to construct NSValues using the core valueWithBytes:objCType: API. This builtin only works with concrete, @objc-representable types for now, which should be sufficient for a stdlib-internal API.

Author: jckarter

include/swift/AST/Builtins.def

@@ -452,6 +452,9 @@ BUILTIN_MISC_OPERATION(UnsafeGuaranteed, "unsafeGuaranteed", "", Special)
 // unsafeGuaranteedEnd has type (Builtin.Int8) -> ()
 BUILTIN_MISC_OPERATION(UnsafeGuaranteedEnd, "unsafeGuaranteedEnd", "", Special)
 
+// getObjCTypeEncoding has type <T> T.Type -> RawPointer
+BUILTIN_MISC_OPERATION(GetObjCTypeEncoding, "getObjCTypeEncoding", "n", Special)
+
 #undef BUILTIN_MISC_OPERATION
 
 // BUILTIN_TYPE_TRAIT_OPERATION - Compile-time type trait operations.

lib/AST/Builtins.cpp

@@ -847,6 +847,15 @@ static ValueDecl *getZeroInitializerOperation(ASTContext &Context,
   return builder.build(Id);
 }
 
+static ValueDecl *getGetObjCTypeEncodingOperation(ASTContext &Context,
+                                                  Identifier Id) {
+  // <T> T.Type -> RawPointer
+  GenericSignatureBuilder builder(Context);
+  builder.addParameter(makeMetatype(makeGenericParam()));
+  builder.setResult(makeConcrete(Context.TheRawPointerType));
+  return builder.build(Id);
+}
+
 static ValueDecl *getAddressOfOperation(ASTContext &Context, Identifier Id) {
   // <T> (@inout T) -> RawPointer
   GenericSignatureBuilder builder(Context);
@@ -1626,6 +1635,9 @@ ValueDecl *swift::getBuiltinValueDecl(ASTContext &Context, Identifier Id) {
   case BuiltinValueKind::IntToFPWithOverflow:
     if (Types.size() != 2) return nullptr;
     return getIntToFPWithOverflowOperation(Context, Id, Types[0], Types[1]);
+
+  case BuiltinValueKind::GetObjCTypeEncoding:
+    return getGetObjCTypeEncodingOperation(Context, Id);
   }
 
   llvm_unreachable("bad builtin value!");

lib/IRGen/GenBuiltin.cpp

@@ -22,6 +22,7 @@
 #include "llvm/ADT/StringSwitch.h"
 #include "swift/AST/Types.h"
 #include "swift/SIL/SILModule.h"
+#include "clang/AST/ASTContext.h"
 
 #include "Explosion.h"
 #include "GenCall.h"
@@ -852,5 +853,18 @@ if (Builtin.ID == BuiltinValueKind::id) { \
     return;
   }
 
+  if (Builtin.ID == BuiltinValueKind::GetObjCTypeEncoding) {
+    args.claimAll();
+    Type valueTy = substitutions[0].getReplacement();
+    // Get the type encoding for the associated clang type.
+    auto clangTy = IGF.IGM.getClangType(valueTy->getCanonicalType());
+    std::string encoding;
+    IGF.IGM.getClangASTContext().getObjCEncodingForType(clangTy, encoding);
+    
+    auto globalString = IGF.IGM.getAddrOfGlobalString(encoding);
+    out.add(globalString);
+    return;
+  }
+  
   llvm_unreachable("IRGen unimplemented for this builtin!");
 }

stdlib/public/core/BridgeObjectiveC.swift

@@ -580,4 +580,16 @@ extension AutoreleasingUnsafeMutablePointer {
   }
 }
 
+/// Get the ObjC type encoding for a type as a pointer to a C string.
+///
+/// This is used by the Foundation overlays. The compiler will error if the
+/// passed-in type is generic or not representable in Objective-C
+@_transparent
+public func _getObjCTypeEncoding<T>(_ type: T.Type) -> UnsafePointer<Int8> {
+  // This must be `@_transparent` because `Builtin.getObjCTypeEncoding` is
+  // only supported by the compiler for concrete types that are representable
+  // in ObjC.
+  return UnsafePointer(Builtin.getObjCTypeEncoding(type))
+}
+
 #endif

test/IRGen/builtins_objc.swift

@@ -0,0 +1,35 @@
+// RUN: %target-swift-frontend -parse-stdlib -primary-file %s -emit-ir | %FileCheck %s
+
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+import Swift
+import Foundation
+
+@objc enum ObjCEnum: Int32 { case X }
+@objc class ObjCClass: NSObject {}
+class NonObjCClass {}
+
+@_silgen_name("use")
+func use(_: Builtin.RawPointer)
+
+
+func getObjCTypeEncoding<T>(_: T) {
+  // CHECK: call void @use({{.* i8]\*}} [[INT32:@[0-9]+]],
+  use(Builtin.getObjCTypeEncoding(Int32.self))
+  // CHECK: call void @use({{.* i8]\*}} [[INT32]]
+  use(Builtin.getObjCTypeEncoding(ObjCEnum.self))
+  // CHECK: call void @use({{.* i8]\*}} [[CGRECT:@[0-9]+]],
+  use(Builtin.getObjCTypeEncoding(CGRect.self))
+  // CHECK: call void @use({{.* i8]\*}} [[NSRANGE:@[0-9]+]],
+  use(Builtin.getObjCTypeEncoding(NSRange.self))
+  // CHECK: call void @use({{.* i8]\*}} [[OBJECT:@[0-9]+]],
+  use(Builtin.getObjCTypeEncoding(AnyObject.self))
+  // CHECK: call void @use({{.* i8]\*}} [[OBJECT]]
+  use(Builtin.getObjCTypeEncoding(NSObject.self))
+  // CHECK: call void @use({{.* i8]\*}} [[OBJECT]]
+  use(Builtin.getObjCTypeEncoding(ObjCClass.self))
+  // CHECK: call void @use({{.* i8]\*}} [[OBJECT]]
+  use(Builtin.getObjCTypeEncoding(NonObjCClass.self))
+}
+