[interop][SwiftToCxx] support @_expose attribute on initializers

Author: hyp

include/swift/AST/Attr.def

@@ -758,7 +758,7 @@ SIMPLE_DECL_ATTR(_alwaysEmitConformanceMetadata, AlwaysEmitConformanceMetadata,
   132)
 
 DECL_ATTR(_expose, Expose,
-  OnFunc | OnNominalType | OnVar |
+  OnFunc | OnNominalType | OnVar | OnConstructor |
   LongAttribute | UserInaccessible |
   ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
   133)

include/swift/AST/DiagnosticsSema.def

@@ -1485,6 +1485,9 @@ ERROR(expose_only_non_other_attr,none,
       "@_expose attribute cannot be applied to an '%0' declaration", (StringRef))
 ERROR(expose_inside_unexposed_decl,none,
       "@_expose attribute cannot be applied inside of unexposed declaration %0", (DeclName))
+ERROR(expose_invalid_name_pattern_init,none,
+      "invalid declaration name '%0' specified in an @_expose attribute; "
+      "exposed initializer name must start with 'init'", (StringRef))
 
 ERROR(attr_methods_only,none,
       "only methods can be declared %0", (DeclAttribute))

lib/PrintAsClang/PrintClangFunction.cpp

@@ -697,6 +697,16 @@ void DeclAndTypeClangFunctionPrinter::printCxxThunkBody(
   }
 }
 
+static StringRef getConstructorName(const AbstractFunctionDecl *FD) {
+  auto name = cxx_translation::getNameForCxx(
+      FD, cxx_translation::CustomNamesOnly_t::CustomNamesOnly);
+  if (!name.empty()) {
+    assert(name.startswith("init"));
+    return name;
+  }
+  return "init";
+}
+
 void DeclAndTypeClangFunctionPrinter::printCxxMethod(
     const NominalTypeDecl *typeDeclContext, const AbstractFunctionDecl *FD,
     StringRef swiftSymbolName, Type resultTy, bool isDefinition) {
@@ -713,8 +723,10 @@ void DeclAndTypeClangFunctionPrinter::printCxxMethod(
   modifiers.isConst =
       !isa<ClassDecl>(typeDeclContext) && !isMutating && !isConstructor;
   auto result = printFunctionSignature(
-      FD, isConstructor ? "init" : cxx_translation::getNameForCxx(FD), resultTy,
-      FunctionSignatureKind::CxxInlineThunk, {}, modifiers);
+      FD,
+      isConstructor ? getConstructorName(FD)
+                    : cxx_translation::getNameForCxx(FD),
+      resultTy, FunctionSignatureKind::CxxInlineThunk, {}, modifiers);
   assert(!result.isUnsupported() && "C signature should be unsupported too");
 
   if (!isDefinition) {

lib/Sema/TypeCheckAttr.cpp

@@ -1865,6 +1865,14 @@ void AttributeChecker::visitExposeAttr(ExposeAttr *attr) {
     diagnose(attr->getLocation(), diag::expose_inside_unexposed_decl,
              decl->getName());
   }
+
+  // Verify that the name mentioned in the expose
+  // attribute matches the supported name pattern.
+  if (!attr->Name.empty()) {
+    if (isa<ConstructorDecl>(VD) && !attr->Name.startswith("init"))
+      diagnose(attr->getLocation(), diag::expose_invalid_name_pattern_init,
+               attr->Name);
+  }
 }
 
 void AttributeChecker::visitUnsafeNoObjCTaggedPointerAttr(

test/Interop/SwiftToCxx/expose-attr/expose-swift-decls-to-cxx.swift

@@ -44,6 +44,12 @@ public struct NotExposedStruct {
 public struct ExposedStructRenamed {
     public var y: Int
 
+    @_expose(Cxx)
+    public init() { y = 42; prop = 0; prop2 = 0; }
+
+    @_expose(Cxx, "initWithValue")
+    public init(why x: Int) { y = x; prop = 0; prop2 = 0; }
+
     @_expose(Cxx, "renamedProp")
     public var prop: Int
 
@@ -74,6 +80,8 @@ public final class ExposedClass {
 // CHECK: ExposedStruct2(ExposedStruct2 &&) = default;
 // CHECK-NEXT: swift::Int getY() const;
 // CHECK-NEXT: void setY(swift::Int value);
+// CHECK-NEXT: static inline ExposedStruct2 init();
+// CHECK-NEXT: static inline ExposedStruct2 initWithValue(swift::Int x);
 // CHECK-NEXT: swift::Int getRenamedProp() const;
 // CHECK-NEXT: void setRenamedProp(swift::Int value);
 // CHECK-NEXT: swift::Int getProp3() const;
@@ -100,6 +108,8 @@ public final class ExposedClass {
 // CHECK: void ExposedStruct::method() const {
 // CHECK: swift::Int ExposedStruct2::getY() const {
 // CHECK: void ExposedStruct2::setY(swift::Int value) {
+// CHECK: ExposedStruct2 ExposedStruct2::init() {
+// CHECK: ExposedStruct2 ExposedStruct2::initWithValue(swift::Int x) {
 // CHECK: swift::Int ExposedStruct2::getRenamedProp() const {
 // CHECK: void ExposedStruct2::setRenamedProp(swift::Int value) {
 // CHECK: swift::Int ExposedStruct2::getProp3() const {

test/attr/attr_expose.swift

@@ -24,3 +24,12 @@ struct NotExposedStruct {
     @_expose(Cxx) // expected-error {{@_expose attribute cannot be applied inside of unexposed declaration 'NotExposedStruct'}}
     func errorOnInnerExpose() {}
 }
+
+@_expose(Cxx)
+struct ExposedStruct {
+    @_expose(Cxx, "create") // expected-error {{invalid declaration name 'create' specified in an @_expose attribute; exposed initializer name must start with 'init'}}
+    init() {}
+
+    @_expose(Cxx, "initWith")
+    init(with y: Int) {}
+}