Deprecate @_unsafeInheritExecutor and remove it from Swift 6

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -4000,6 +4000,9 @@ ERROR(inherits_executor_without_async,none,
 ERROR(isolation_in_inherits_executor,none,
       "#isolation%select{| (introduced by a default argument)}0 cannot be used "
       "within an '@_unsafeInheritExecutor' function", (bool))
+ERROR(unsafe_inherits_executor_deprecated,none,
+        "@_unsafeInheritExecutor attribute is deprecated; consider an "
+        "'isolated' parameter defaulted to '#isolation' instead", ())
 
 ERROR(lifetime_invalid_global_scope,none, "%0 is only valid on methods",
       (DeclAttribute))

lib/Sema/TypeCheckAttr.cpp

@@ -7279,6 +7279,13 @@ void AttributeChecker::visitUnsafeInheritExecutorAttr(
   auto fn = cast<FuncDecl>(D);
   if (!fn->isAsyncContext()) {
     diagnose(attr->getLocation(), diag::inherits_executor_without_async);
+  } else {
+    bool inConcurrencyModule = D->getDeclContext()->getParentModule()->getName()
+        .str().equals("_Concurrency");
+    auto diag = fn->diagnose(diag::unsafe_inherits_executor_deprecated);
+    diag.warnUntilSwiftVersion(6);
+    diag.limitBehaviorIf(inConcurrencyModule, DiagnosticBehavior::Warning);
+    replaceUnsafeInheritExecutorWithDefaultedIsolationParam(fn, diag);
   }
 }
 

lib/Sema/TypeCheckConcurrency.cpp

@@ -2054,9 +2054,7 @@ static std::pair<SourceLoc, bool> adjustPoundIsolationDiagLoc(
   };
 }
 
-/// Replace the @_unsafeInheritExecutor with a defaulted isolation
-/// parameter.
-static void replaceUnsafeInheritExecutorWithDefaultedIsolationParam(
+void swift::replaceUnsafeInheritExecutorWithDefaultedIsolationParam(
     AbstractFunctionDecl *func, InFlightDiagnostic &diag) {
   auto attr = func->getAttrs().getAttribute<UnsafeInheritExecutorAttr>();
   assert(attr && "Caller didn't validate the presence of the attribute");

lib/Sema/TypeCheckConcurrency.h

@@ -651,6 +651,11 @@ bool diagnoseApplyArgSendability(
 /// If the enclosing function has @_unsafeInheritExecutorAttr, return it.
 AbstractFunctionDecl *enclosingUnsafeInheritsExecutor(const DeclContext *dc);
 
+/// Add Fix-Its to the given function to replace the @_unsafeInheritExecutor
+/// attribute with a defaulted isolation parameter.
+void replaceUnsafeInheritExecutorWithDefaultedIsolationParam(
+    AbstractFunctionDecl *func, InFlightDiagnostic &diag);
+
 } // end namespace swift
 
 namespace llvm {

test/Concurrency/unsafe_inherit_executor.swift

@@ -11,6 +11,7 @@ func testNonAsync() {}
 
 @_unsafeInheritExecutor
 func testAsync() async {}
+// expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead}}
 
 struct A {
   // expected-error @+1 {{@_unsafeInheritExecutor may only be used on 'func' declarations}}
@@ -23,6 +24,7 @@ struct A {
 
   @_unsafeInheritExecutor
   func testAsync() async {}
+  // expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead}}
 }
 
 
@@ -32,6 +34,7 @@ class NonSendableObject {
 
 @_unsafeInheritExecutor
 func useNonSendable(object: NonSendableObject) async {}
+// expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead; this is an error in the Swift 6 language mode}}{{35:1-24=}}{{36:46-46=, isolation: isolated (any Actor)? = #isolation}}
 
 actor MyActor {
   var object = NonSendableObject()
@@ -46,23 +49,32 @@ func inheritsIsolationProperly(isolation: isolated (any Actor)? = #isolation) as
 // @_unsafeInheritExecutor does not work with #isolation
 @_unsafeInheritExecutor
 func unsafeCallerA(x: Int) async {
+  // expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead}}
+
   await inheritsIsolationProperly()
-  // expected-error@-1{{#isolation (introduced by a default argument) cannot be used within an '@_unsafeInheritExecutor' function}}{{47:1-24=}}{{48:26-26=, isolation: isolated (any Actor)? = #isolation}}
+  // expected-error@-1{{#isolation (introduced by a default argument) cannot be used within an '@_unsafeInheritExecutor' function}}{{50:1-24=}}{{51:26-26=, isolation: isolated (any Actor)? = #isolation}}
+t 6)
 }
 
 @_unsafeInheritExecutor
 func unsafeCallerB() async {
+  // expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead}}
+
   await inheritsIsolationProperly(isolation: #isolation)
-  // expected-error@-1{{#isolation cannot be used within an '@_unsafeInheritExecutor' function}}{{53:1-24=}}{{54:20-20=isolation: isolated (any Actor)? = #isolation}}
+  // expected-error@-1{{#isolation cannot be used within an '@_unsafeInheritExecutor' function}}{{58:1-24=}}{{59:20-20=isolation: isolated (any Actor)? = #isolation}}
 }
 
 @_unsafeInheritExecutor
 func unsafeCallerC(x: Int, fn: () -> Void, fn2: () -> Void) async {
+  // expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead}}
+
   await inheritsIsolationProperly()
-  // expected-error@-1{{#isolation (introduced by a default argument) cannot be used within an '@_unsafeInheritExecutor' function}}{{59:1-24=}}{{60:28-28=, isolation: isolated (any Actor)? = #isolation, }}
+  // expected-error@-1{{#isolation (introduced by a default argument) cannot be used within an '@_unsafeInheritExecutor' function}}{{66:1-24=}}{{67:28-28=, isolation: isolated (any Actor)? = #isolation, }}
 }
 
 @_unsafeInheritExecutor
 func unsafeCallerAvoidsNewLoop(x: some AsyncSequence<Int, Never>) async throws {
+  // expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead}}
+
   for try await _ in x { }
 }