Sema: Reject invalid 'reasync' functions

Author: slavapestov

include/swift/AST/DiagnosticsSema.def

@@ -3015,6 +3015,8 @@ ERROR(rethrows_without_throwing_parameter,none,
 ERROR(override_reasync_with_non_reasync,none,
       "override of 'reasync' %select{method|initializer}0 should also "
       "be 'reasync'", (bool))
+ERROR(reasync_without_async_parameter,none,
+      "'reasync' function must take an 'async' function argument", ())
 
 ERROR(autoclosure_function_type,none,
       "@autoclosure attribute only applies to function types",

lib/Sema/TypeCheckAttr.cpp

@@ -131,6 +131,8 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   IGNORED_ATTR(NoDerivative)
   IGNORED_ATTR(SpecializeExtension)
   IGNORED_ATTR(Concurrent)
+  IGNORED_ATTR(AtRethrows)
+  IGNORED_ATTR(AtReasync)
 #undef IGNORED_ATTR
 
   void visitAlignmentAttr(AlignmentAttr *attr) {
@@ -225,7 +227,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   void visitNSCopyingAttr(NSCopyingAttr *attr);
   void visitRequiredAttr(RequiredAttr *attr);
   void visitRethrowsAttr(RethrowsAttr *attr);
-  void visitAtRethrowsAttr(AtRethrowsAttr *attr);
 
   void checkApplicationMainAttribute(DeclAttribute *attr,
                                      Identifier Id_ApplicationDelegate,
@@ -280,7 +281,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   void visitMarkerAttr(MarkerAttr *attr);
 
   void visitReasyncAttr(ReasyncAttr *attr);
-  void visitAtReasyncAttr(AtReasyncAttr *attr);
 };
 } // end anonymous namespace
 
@@ -2054,8 +2054,8 @@ void AttributeChecker::visitRequiredAttr(RequiredAttr *attr) {
 }
 
 void AttributeChecker::visitRethrowsAttr(RethrowsAttr *attr) {
-  // 'rethrows' only applies to functions that take throwing functions
-  // as parameters.
+  // Make sure the function takes a 'throws' function argument or a
+  // conformance to a '@rethrows' protocol.
   auto fn = dyn_cast<AbstractFunctionDecl>(D);
   if (fn->getPolymorphicEffectKind(EffectKind::Throws)
         != PolymorphicEffectKind::Invalid) {
@@ -2066,8 +2066,6 @@ void AttributeChecker::visitRethrowsAttr(RethrowsAttr *attr) {
   attr->setInvalid();
 }
 
-void AttributeChecker::visitAtRethrowsAttr(AtRethrowsAttr *attr) {}
-
 /// Collect all used generic parameter types from a given type.
 static void collectUsedGenericParameters(
     Type Ty, SmallPtrSetImpl<TypeBase *> &ConstrainedGenericParams) {
@@ -5489,10 +5487,17 @@ void AttributeChecker::visitMarkerAttr(MarkerAttr *attr) {
 }
 
 void AttributeChecker::visitReasyncAttr(ReasyncAttr *attr) {
-  // FIXME
-}
+  // Make sure the function takes a 'throws' function argument or a
+  // conformance to a '@rethrows' protocol.
+  auto fn = dyn_cast<AbstractFunctionDecl>(D);
+  if (fn->getPolymorphicEffectKind(EffectKind::Async)
+        != PolymorphicEffectKind::Invalid) {
+    return;
+  }
 
-void AttributeChecker::visitAtReasyncAttr(AtReasyncAttr *attr) {}
+  diagnose(attr->getLocation(), diag::reasync_without_async_parameter);
+  attr->setInvalid();
+}
 
 namespace {
 

test/Concurrency/reasync.swift

@@ -14,6 +14,13 @@ func asyncReasyncFunction(_: () async throws -> ()) async reasync {}
 func reasyncParam(_: () reasync -> ()) {}
 // expected-error@-1 {{only function declarations may be marked 'reasync'; did you mean 'async'?}}{{25-32=async}}
 
+//// Invalid cases
+
+func noReasyncParams() reasync {}
+// expected-error@-1 {{'reasync' function must take an 'async' function argument}}
+
+//// Method override attribute checking
+
 class Base {
   func reasyncMethod(_: () async -> ()) reasync {}
   // expected-note@-1 {{overridden declaration is here}}
@@ -22,4 +29,4 @@ class Base {
 class Derived : Base {
   override func reasyncMethod(_: () async -> ()) async {}
   // expected-error@-1 {{override of 'reasync' method should also be 'reasync'}}
-}
+}