[cxx-interop] Mark operator! as prefix func

Prefix operators in Swift need to be marked as `prefix func`.

For example, the lack of `prefix` attribute prevents the user from conforming a C++ type that defines `operator!` to a Swift protocol that requires `static prefix func !(obj: Self) -> Self`.

Author: egorzhdan

lib/ClangImporter/SwiftDeclSynthesizer.cpp

@@ -1881,9 +1881,13 @@ synthesizeOperatorMethodBody(AbstractFunctionDecl *afd, void *context) {
 FuncDecl *
 SwiftDeclSynthesizer::makeOperator(FuncDecl *operatorMethod,
                                    clang::CXXMethodDecl *clangOperator) {
+  clang::OverloadedOperatorKind opKind = clangOperator->getOverloadedOperator();
+
+  assert(opKind != clang::OverloadedOperatorKind::OO_None &&
+         "expected a C++ operator");
+
   auto &ctx = ImporterImpl.SwiftContext;
-  auto opName =
-      clang::getOperatorSpelling(clangOperator->getOverloadedOperator());
+  auto opName = clang::getOperatorSpelling(opKind);
   auto paramList = operatorMethod->getParameters();
   auto genericParamList = operatorMethod->getGenericParams();
 
@@ -1935,6 +1939,11 @@ SwiftDeclSynthesizer::makeOperator(FuncDecl *operatorMethod,
   topLevelStaticFuncDecl->setBodySynthesizer(synthesizeOperatorMethodBody,
                                              operatorMethod);
 
+  // If this is a unary prefix operator (e.g. `!`), add a `prefix` attribute.
+  if (clangOperator->param_empty()) {
+    topLevelStaticFuncDecl->getAttrs().add(new (ctx) PrefixAttr(SourceLoc()));
+  }
+
   return topLevelStaticFuncDecl;
 }
 

test/Interop/Cxx/operators/member-inline-module-interface.swift

@@ -9,7 +9,7 @@
 // CHECK: }
 
 // CHECK: struct LoadableBoolWrapper {
-// CHECK:   static func ! (lhs: inout LoadableBoolWrapper) -> LoadableBoolWrapper
+// CHECK:   prefix static func ! (lhs: inout LoadableBoolWrapper) -> LoadableBoolWrapper
 // CHECK: }
 
 // CHECK: struct AddressOnlyIntWrapper {

test/Interop/Cxx/operators/member-inline-silgen.swift

@@ -16,7 +16,7 @@ public func exclaim(_ wrapper: inout LoadableBoolWrapper) -> LoadableBoolWrapper
 // CHECK: bb0([[SELF:%.*]] : $*LoadableBoolWrapper):
 // CHECK:   [[METATYPE:%.*]] = metatype $@thin LoadableBoolWrapper.Type
 // CHECK:   [[SELFACCESS:%.*]] = begin_access [modify] [static] [[SELF]] : $*LoadableBoolWrapper
-// CHECK:   [[OP:%.*]] = function_ref @$sSo19LoadableBoolWrapperV1noiyA2BzFZ : $@convention(method) (@inout LoadableBoolWrapper, @thin LoadableBoolWrapper.Type) -> LoadableBoolWrapper
+// CHECK:   [[OP:%.*]] = function_ref @$sSo19LoadableBoolWrapperV1nopyA2BzFZ : $@convention(method) (@inout LoadableBoolWrapper, @thin LoadableBoolWrapper.Type) -> LoadableBoolWrapper
 // CHECK:   apply [[OP]]([[SELFACCESS]], [[METATYPE]]) : $@convention(method) (@inout LoadableBoolWrapper, @thin LoadableBoolWrapper.Type) -> LoadableBoolWrapper
 // CHECK:   end_access [[SELFACCESS]]