[Sema] Validate that @_inheritActorContext is used only on @Sendable/sending and async/@isolated(any) parameters

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -8602,6 +8602,16 @@ ERROR(inherit_actor_context_only_on_func_types,none,
       "%0 only applies to parameters with function types (got: %1)",
       (DeclAttribute, Type))
 
+ERROR(inherit_actor_context_only_on_sending_or_Sendable_params,none,
+      "%0 only applies to 'sending' parameters or parameters with "
+      "'@Sendable' function types",
+      (DeclAttribute))
+
+ERROR(inherit_actor_context_only_on_async_or_isolation_erased_params,none,
+      "%0 only applies to '@isolated(any)' parameters or parameters with "
+      "asynchronous function types",
+      (DeclAttribute))
+
 //===----------------------------------------------------------------------===//
 // MARK: @concurrent and nonisolated(nonsending) attributes
 //===----------------------------------------------------------------------===//

lib/Sema/TypeCheckAttr.cpp

@@ -7861,6 +7861,24 @@ void AttributeChecker::visitInheritActorContextAttr(
                           attr, paramTy);
     return;
   }
+
+  // The type has to be either `@Sendable` or `sending` _and_
+  // `async` or `@isolated(any)`.
+  if (!(funcTy->isSendable() || P->isSending())) {
+    diagnose(attr->getLocation(),
+             diag::inherit_actor_context_only_on_sending_or_Sendable_params,
+             attr)
+        .warnUntilFutureSwiftVersion();
+  }
+
+  // Eiether `async` or `@isolated(any)`.
+  if (!(funcTy->isAsync() || funcTy->getIsolation().isErased())) {
+    diagnose(
+        attr->getLocation(),
+        diag::inherit_actor_context_only_on_async_or_isolation_erased_params,
+        attr)
+        .warnUntilFutureSwiftVersion();
+  }
 }
 
 void AttributeChecker::visitMarkerAttr(MarkerAttr *attr) {

test/ASTGen/attrs.swift

@@ -257,5 +257,5 @@ struct AnyEraser: EraserProto {
   init<T: EraserProto>(erasing: T) {}
 }
 
-func takeNone(@_inheritActorContext param: () async -> ()) { }
-func takeAlways(@_inheritActorContext(always) param: () async -> ()) { }
+func takeNone(@_inheritActorContext param: @Sendable () async -> ()) { }
+func takeAlways(@_inheritActorContext(always) param: sending @isolated(any) () -> ()) { }