[Distributed] Ban inout, varargs from dist funcs

Author: ktoso

include/swift/AST/DiagnosticsSema.def

@@ -4522,6 +4522,15 @@ ERROR(distributed_actor_func_nonisolated, none,
 ERROR(distributed_actor_func_private, none,
       "%0 %1 cannot be 'private'",
       (DescriptiveDeclKind, DeclName))
+ERROR(distributed_actor_func_inout, none,
+      "%0 %1 cannot declare 'inout' argument %2",
+      (DescriptiveDeclKind, DeclName, DeclName))
+ERROR(distributed_actor_func_closure, none,
+      "%0 %1 cannot declare closure arguments, as they cannot be serialized",
+      (DescriptiveDeclKind, DeclName))
+ERROR(distributed_actor_func_variadic, none,
+      "%0 %1 cannot declare variadic argument %2",
+      (DescriptiveDeclKind, DeclName, DeclName))
 ERROR(distributed_actor_remote_func_is_not_static,none,
       "remote function %0 must be static.",
       (DeclName))

lib/Sema/TypeCheckDistributed.cpp

@@ -128,6 +128,23 @@ bool swift::checkDistributedFunction(FuncDecl *func, bool diagnose) {
       // TODO: suggest a fixit to add Codable to the type?
       return true;
     }
+
+    if (param->isInOut()) {
+      param->diagnose(
+          diag::distributed_actor_func_inout,
+          func->getDescriptiveKind(), func->getName(),
+          param->getName()
+      ); // TODO(distributed): offer fixit to remove 'inout'
+      return true;
+    }
+
+    if (param->isVariadic()) {
+      param->diagnose(
+          diag::distributed_actor_func_variadic,
+          func->getDescriptiveKind(), func->getName(),
+          param->getName()
+      );
+    }
   }
 
   // --- Result type must be either void or a codable type

test/Distributed/distributed_actor_inference.swift

@@ -68,9 +68,9 @@ distributed actor SomeDistributedActor_6 {
 
 @available(SwiftStdlib 5.6, *)
 distributed actor SomeDistributedActor_7 {
-  distributed func dont_1() async throws -> Int { 42 } // expected-error{{distributed function's 'dont_1' remote counterpart '_remote_dont_1' cannot not be implemented manually.}}
-  distributed func dont_2() async throws -> Int { 42 } // expected-error{{distributed function's 'dont_2' remote counterpart '_remote_dont_2' cannot not be implemented manually.}}
-  distributed func dont_3() async throws -> Int { 42 } // expected-error{{distributed function's 'dont_3' remote counterpart '_remote_dont_3' cannot not be implemented manually.}}
+  distributed func dont_1() async throws -> Int { 42 } // expected-error{{distributed instance method's'dont_1' remote counterpart '_remote_dont_1' cannot not be implemented manually.}}
+  distributed func dont_2() async throws -> Int { 42 } // expected-error{{distributed instance method's'dont_2' remote counterpart '_remote_dont_2' cannot not be implemented manually.}}
+  distributed func dont_3() async throws -> Int { 42 } // expected-error{{distributed instance method's'dont_3' remote counterpart '_remote_dont_3' cannot not be implemented manually.}}
 }
 
 @available(SwiftStdlib 5.6, *)

test/Distributed/distributed_actor_isolation.swift

@@ -75,6 +75,18 @@ distributed actor DistributedActor_1 {
     fatalError()
   }
 
+  distributed func varargs(int: Int...) {
+    // expected-error@-1{{distributed instance method 'varargs(int:)' cannot declare variadic argument 'int'}}
+  }
+
+  distributed func closure(close: () -> String) {
+    // expected-error@-1{{distributed instance method parameter 'close' of type '() -> String' does not conform to 'Codable'}}
+  }
+
+  distributed func noInout(inNOut burger: inout String) {
+    // expected-error@-1{{distributed instance method 'noInout(inNOut:)' cannot declare 'inout' argument 'burger'}}
+  }
+
   distributed func distReturnGeneric<T: Codable & Sendable>(item: T) async throws -> T { // ok
     item
   }